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| Meta Title | Cable Size Calculator AS/NZS 3008 | jCalc.net |
| Meta Description | Cable size calculator for current rating, voltage drop, loop impedance, earth cable and short circuit, based on Australia and New Zealand standard AS/NZS 3008. |
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| Boilerpipe Text | See Also
Maximum Demand Calculator AS/NZS 3000
Arc Flash Calculator IEEE 1584
Standard parameters
Standard:
Select the relevant part in AS/NZS 3008: 2017.
Part 1:
Australian conditions. Air 40°C. Soil 25°C.
Part 2:
New Zealand conditions. Air 30°C. Soil 15°C.
The differences between the parts are:
Rating tables, Table 4 to 15.
Air temperature derating, Table 27(1).
Soil temperature derating, Table 27(2).
Load parameters
Phase:
Select the phase arrangement.
Voltage (V):
Select the voltage. If the voltage is not available in the select list, choose "Other" and specify any value in the ranges shown below.
Specify voltage (V):
Specify any voltage in the following ranges.
min
max
Three-phase AC
Two-phase 120°
Two-phase 180°
1 V
1,000 V
phase-to-phase
Single-phase AC
DC
1 V
1,000 V
phase-to-neutral
Rating:
Specify the load rating in kW, kVA, A, or hp.
When the rating is in ampere, enter the
per‑phase
line current for 3‑phase systems. For example, enter only 100 A in the following scenario.
Phase 1 line current
100 A
Phase 2 line current
100 A
Phase 3 line current
100 A
Enter only 100 A
Note: It is the line current (not the delta winding current) for three-phase motors.
PF:
Specify the load power factor when the load rating is specified in kW or hp.
It is also required for A and kVA ratings when the
Load Power Factor
option is selected as Specified under
Advanced Voltage Drop
options.
Voltage drop parameters
Max. volt drop (%):
Select the maximum allowable voltage drop at the load. Select Other to specify a custom value.
Specify max. volt drop (%):
Specify any voltage drop between 0.01 % and 100 %.
Distance (m):
The cable length in meters from the source to the load. The return length is automatically included by the calculator for single-phase and three-phase installations.
Advanced options:
Select to show the following two options.
Conductor temperature:
Select Calculate or Maximum.
Calculate (default)
The calculated operating temperature is used to select the cable
resistance
for voltage drop calculations. Read more
here
.
Maximum
The maximum rated temperature of the insulation is used to select the cable
resistance
for voltage drop calculations. This is the most conservative option.
Load power factor:
Worst-case or Specified.
Worst case (default)
The worst-case power factor is used to calculate the voltage drop. This is the most conservative option. Read more
here
.
Specified
The specified power factor of the load is used to calculate the voltage drop. Read more
here
.
Active cable parameters
Insulation:
Select the insulation for the cables.
For multi-core cables, this applies to the live, neutral, and earth conductors.
For single-core cables, this applies to the live and neutral conductors.
The earth cable is selected under
Earth Cable Insulation
.
PVC
Max. operating temp.
V-90
Standard.
Most popular insulation.
May be operated at 90°C temporarily, with no mechanical pressure on the insulation.
75°C
V-90HT
High temperature.
May be operated at 105°C temporarily, with no mechanical pressure on the insulation.
75°C
V-75
Traditional (older) type PVC cables.
75°C
XLPE
X-90
Standard.
Most popular XLPE insulation.
90°C
X-HF-90
Fire rated.
90°C
X-110
High temperature.
110°C
X-HF-110
High temperature.
Fire rated.
110°C
Elastomer (rubber)
R-EP-90
Standard.
90°C
R-HF-90
Fire rated.
90°C
R-E-110
High temperature.
110°C
R-HF-110
High temperature.
Fire rated.
110°C
Cable type:
Select the cable type as shown below.
1 Phase AC or DC
Multi-core 2C+E
One live core.
One neutral core.
One earth core.
Multi-core 2C (mains)
One live core.
One combined earth and neutral core.
Single-cores 2x1C+E
One live cable.
One neutral cable.
One earth cable.
Single-cores 2x1C (mains)
One live cable.
One combined earth and neutral cable.
3 Phase AC
Multi-core 3C+E
Three-phase cores.
One earth core.
Multi-core 4C+E
Three-phase cores.
One neutral core.
One earth core.
Multi-core 4C (mains)
Three-phase cores.
One combined earth and neutral core.
Single-cores 3x1C+E
Three-phase cables.
One earth cable.
Single-cores 4x1C+E
Three-phase cables.
One neutral cable.
One earth cable.
Single-cores 4x1C (mains)
Three-phase cables.
One combined earth and neutral core.
Flexible:
Select if a flexible cable is used.
Conductor:
Select Copper or Aluminium.
Active size (mm
2
):
Select a conductor size or select Auto.
The Auto option will automatically select the smallest cable that meets the following criteria.
Current rating.
Voltage drop.
Fault current rating.
Loop impedance.
Protection device thermal trip current.
This applies to the live and neutral conductors.
Use parallel cables (or cable groups):
Enables the use of parallel mutli-core cables, or parallel single-core
cable groups
in a circuit for high-current installations. This means more than one one live core per phase. The minimum allowable size for parallel cables is 4 mm
2
, as specified in AS/NZS 3000.
Parallel cables are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Number of parallel cables (or cable groups):
The number of parallel multi-core cables or parallel single-core
cable groups
in this circuit.
This is when you want to use parallel multi-core cables or single-core cable groups in a circuit to increase the current rating or reduce the voltage drop.
For single-core cables, the whole
cable group
is counted as one. The
cable group
includes the three-phase cables, the neutral cable, and the earth cable. It can be installed in a flat or trefoil formation.
Parallel cables are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Examples:
Three parallel multi-core cables
Three parallel single-core cable groups
Earth cable parameters
Earth cable insulation:
Applicable to single-core cables. It can be different from the active cable insulation.
The options are the same as the
active cable insulation options.
Flexible earth:
Applicable to single-core cables. Select if a flexible earth cable is used.
Earth conductor:
Applicable to single-core cables. Select Copper or Aluminium. Note that you cannot select Aluminium for a copper active cable. Please let me know if you need to.
Earth core size (mm
2
):
Select an earth cable size or select Auto.
Multi-core cables
Only Auto is supported for multi-core cables.
The calculator will select the minimum copper earth size from
Table 5.1
in AS/NZS 3000. These sizes match commercial copper multi-core cables.
For aluminium cables the calculator will select an earth size equal to the active size. This matches most commercial aluminium cables.
The fault current rating and loop impedance requirements are checked if
Check fault rating
and
Check loop impedance
are enabled. It does not increase the earth size.
Parallel multi-core cables
The earth fault rating is checked per earth core, i.e. no earth fault current split is considered.
The loop impedenace is checked on the combination of parallel active and earth cores, i.e. an equal earth fault current split is considered.
Single-core cables
Single-core cables support Auto and Manual selection of the earth size.
To select a specific earth size, select a specific active size first.
In Auto, the selection process is as follows:
Step 1: The calculator begins with the minimum recommended earth size
Table 5.1
in AS/NZS 3000.
Step 2: If
Check fault rating
and
Check loop impedance
are enabled, the calculator increases the earth cable size until both the fault current rating and loop impedance requirements are met.
Step 3: If no suitable earth size is found, the active size is used. If you need a larger earth cable, select it manually.
If the earth core size is selected manually, the selected earth size is still checked against
Table 5.1
. The fault rating and earth loop impedance are also checked when these options are selected.
Table 5.1
does not specify aluminium earth sizes. They are calculated based on the impedance and fault rating of the equivalent copper earth cables. Click
here
for more details.
Parallel single-core cables
By default, the earth fault rating is checked per earth cable, i.e. no earth fault current split is considered.
However, in high current installations, the option
Combined fault rating
can be enabled, and earth fault rating will be based on an equal split of fault current across parallel earth cables. See
Combined fault rating
for more information.
The loop impedance is checked on the combination of parallel active and earth cables, i.e. an equal earth fault current split is considered.
For parallel active and parallel earth cables, the combined active size is calculated as:
\(S_{active\_combined} = \dfrac {S_{active} \cdot m}{n} \)
Where,
S
active
is the size of one of the active cables in mm
2
.
m
is the number of parallel phase cables.
n
is the number of parallel earth cables.
The combined active size is then used to select the minimum earth size from
Table 5.1
.
For multiple earth cables, the calculator checks that each earth cable is equal to or larger than the minimum earth cable required for one individual active conductor.
For example, in
Table 5.1
the minimum earth cable size for a 240 mm
2
active cable is 95 mm
2
. If two earth cables are selected, the minimum individual earth cable size is still 95 mm
2
.
If the combined active size is larger than 630 mm
2
, the earth size is calculated according to
Table 5.1
as follows:
Copper: Minimum 25% of the combined active size.
Aluminium: Minimum 40% of the combined active size.
For high current installations, the option
Ignore table 5.1
can be enabled, and
Table 5.1
will be enforced up to 120 mm
2
(copper) or 240 mm
2
(aluminium) only. See
Ignore table 5.1
for more information.
Number of earth cores or cables:
Multi-core cables
Matches the number of parallel cables.
Cannot be changed.
One single-core
cable group
One or two earth cables.
Multiple single-core
cable groups
Any number of earth cables between one and the number of parallel cable groups.
Advanced options:
Select to show the following two options.
Ignore table 5.1 sizes:
Ignores earth sizes specified in
Table 5.1
in AS/NZS 3000. Earth size will be based on earth fault current and loop impedance only.
This allows for more economical earth cable sizes.
This option is only available for:
Three-phase, single-core cables, excluding mains.
Number of parallel cable groups > 1.
Check fault rating
and
Check loop impedance
are enabled.
The calculated earth size is ≥ 120 mm
2
(copper) or ≥ 240 mm
2
(aluminium).
Combined earth fault rating:
The fault rating of the earth cables is based on an equal split of earth fault current across the parallel earth cables.
This allows for more economical earth cable sizes.
This option is only available for:
Three-phase, single-core cables, excluding mains.
Number of parallel cable groups > 1.
Number of parallel earth cables > 1.
Check fault rating
and
Check loop impedance
are enabled.
The calculated earth size is ≥ 120 mm
2
(copper) or ≥ 240 mm
2
(aluminium).
Important:
To ensure safety, it is essential that the parallel earth cables:
are the same length,
follow the same route,
are mechanically protected,
insulated,
and separated from the live cables to prevent direct faults between phase and earth cables.
Installation parameters
Formation:
Trefoil or laid flat.
Installation method:
Select the installation method.
Consider the worst-case section of the cable installation.
Which is the installation section with the lowest current rating.
Installation derating parameters
Show derating options:
Check this box if you want to specify derating options. If not, the following default derating options are used.
Australian conditions
New Zealand conditions
Number of cables or cable groups
1
1
Air temperature
40 °C
30 °C
Soil temperature
25 °C
15 °C
Cable depth
0.5 m
0.5 m
Soil resistivity
1.2 °C.m/W
1.2 °C.m/W
Circuit derating
None
None
Cable support:
The cable support options depend on the installation method.
Number of cables (or cable groups):
The number of multi-core cables or single-core
cable groups
in this installation. This includes parallel cables in this circuit and cables from any other circuits included in the same installation.
The standard refers to this parameter as the Number of Circuits. And the standard treats parallel cables as multiple circuits. jCalc uses the names "Number of cables" and "Number of cable groups" instead of "Number of Circuits" to make it more intuitive, especially when parallel cables are used.
Note that the parameter
number of parallel cables (or cable groups)
under Cable Type specifies the number of parallel cables in this circuit only. This parameter considers the parallel cables in this circuit, and cables from any other circuits in the same installation.
All cables in the installation must be considered, because heat from adjacent cables affects the current rating and voltage drop.
For multi-core cables, each cable is considered in the derating. For single-core
cable groups
, each cable group is considered in the derating -not the individual cables for each phase, the neutral or the earth.
Multiple cables (or cable-groups) are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Examples:
Multi-core (number of cables = 3)
Single-core (number of
cable groups
= 3)
Space between cables, cable groups or enclosures:
Select the spacing between multi-core cables, single-core
cable groups
or enclosures (underground multi- and single-core).
The table below shows the spacing that can be selected for different installations and cable types.
In air, multi-core cables
Space between the
edges
of cables.
Touching
Spaced 1D
The diameter of the largest cable.
In air, single-core cables
Space between the
edges
of
cable groups
.
Touching
Spaced 1D
The diameter of the largest cable.
Underground, multi-core cables
Space between the
centres
of cables.
Touching
Buried direct
Underground enclosure
150 mm
300 mm
450 mm
600 m
Underground, single-core cables
Space between the
centres
of
cable groups
.
Touching
Buried direct
Underground enclosure
150 mm
300 mm
450 mm
600 m
Number of tiers:
Number of tiers.
No of horizontally tiered racks:
The number of horizontal tiers (rows) of racks or ladders installed above each other.
The minimum vertical space between racks is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
No of horizontally tiered unperforated trays:
The number of horizontal tiers (rows) of trays installed above each other.
The minimum vertical space between trays is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
No of horizontally tiered perforated trays:
The number of horizontal tiers (rows) of trays installed above each other.
The minimum vertical space between trays is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
No of vertical back-to-back perforated trays:
On or two vertical back-to-back trays. The minimum vertical space between trays is 230mm.
ee AS/NZS 3008:2017 Tables 23 and 24.
Air temperature (°C):
For cables installed in air. The defaults (no derating) are.
Australian conditions: 40°C
New Zealand conditions: 30°C
Soil temperature (°C):
For cables installed underground. The defaults (no derating) are:
Australian conditions: 25°C
New Zealand conditions: 15°C
Cable depth (m):
The default (no derating) is 0.5 m.
Soil resistivity (°C.m/W):
The default (no derating) is 1.2 °C.m/W.
Conduit parameters
Calculate conduit:
Check this box if you want to calculate conduit sizing. The option will only show for installations with enclosures. Conduit sizing is based on Tables C10, C11 and C12 in AS/NZS 3000:2018. Click
here
for more details.
Conduit type:
Select the conduit type. Click
here
for more details.
Conduit size (mm):
Select a conduit size or select Auto. Click
here
for more details.
Short circuit protection parameters
Check short circuit rating:
Select to check the fault rating of the cable.
Check loop impedance:
Select to check the earth loop impedance of the circuit.
In other words, check if the specified protection device will trip for an earth fault when the specified cable is used.
The external source impedance is estimated, calculated, or specified (measured). The method depends on the selected
protection device
.
When it is calculated, it is calculated from the prospective earth fault current.
Protection device
Loop impedance method
MCB
Estimated, Calculated or Measured
MCCB
Calculated
Generic device
Calculated
Protection:
Select the protection device. MCB, MCCB, or Generic.
Protection device
Description
MCB
Miniature circuit breakers. From 1 A to 125 A.
MCCB
Moulded case circuit breakers. From 16 A to 3200 A.
Generic device
Generic phase and earth current fault protection.
With definite time settings.
Short circuit protection parameters -MCB
MCB curve type:
The MCB tripping curve: B, C or D.
MCBs are manufactured according to AS/NZS 60898.1, which specifies trip current ranges for the MCB curve types.
Calculations in AS/NZS 3000 and jCalc is based on the mean values of the ranges.
Curve
type
Trip current
AS/NZS 60898.1
Trip current
AS/NZS 3000
and jCalc
B
3-5 x rated current
4 x rated current
C
5-10 x rated current
7.5 x rated current
D
10-20 x rated current
12.5 x rated current
MCB rating:
Select an MCB rating or select Auto.
The auto option will automatically select the recommended size from Tables C6 and C7 in AS/NZS 3000-2018.
In Auto, the MCB size is selected for the load current. And then checked against the cable.
Source impedance:
Specify the method to determine the source (external) loop impedance.
Estimate:
Estimate according to AS/NZS 3000-2018, i.e. assume that 80% voltage is available at the cable source during an earth fault.
Calculate:
Calculate from the prospective fault current.
Measured:
Specify the measured impedance in Ohm.
Prospective earth fault current (kA):
Specify the prospective earth fault current on the primary side of the circuit breaker.
This parameter is required when the
source impedance method
is selected as "Calculate".
It is used to calculate the external source loop impedance for earth faults.
Short circuit protection parameters -MCCB
Make:
Select between Schneider and Terasaki TemBreak Pro.
Model:
Select the model. Note that the number in the model name represents the current rating of the circuit breaker. For example, a Schneider NXS100 is rated for 100A, and a Terasaki P250 for 250A.
CB fault rating:
The fault current rating of the circuit breaker. This affects the let-though energy.
Trip unit:
Select between Thermal Magnetic, Micrologic 2.3 (NSX) or Micrologic 2.0. (NS)
Thermal-magnetic
Trip unit rating:
Select the current rating or select Auto.
The following are automatically selected in Auto: trip unit rating, thermal trip setting, and magnetic trip setting.
The trip unit rating, and the thermal trip setting, are selected to be ≥ the load current.
Thermal trip:
The thermal trip setting can be selected if the trip unit rating is selected manually.
Magnetic trip:
The magnetic trip setting can be selected if the trip unit rating is selected manually.
Micrologic 2.3 (NSX) and Micrologic 2.0 (NS)
Trip unit rating:
Select the current rating or select Auto.
The following are automatically selected in Auto: trip unit rating, thermal trip setting, short-time trip setting, and instantaneous trip setting.
The trip unit rating, and the thermal trip setting, are selected to be ≥ the load current.
The short-time trip setting is selected as 6x the thermal trip setting.
Thermal trip:
The thermal trip setting can be selected if the trip unit rating is selected manually.
Short-time trip:
The short-time trip setting can be selected if the trip unit rating is selected manually.
Instantaneous trip:
The instantaneous trip setting can be selected if the trip unit rating is selected manually.
Note that there is no instantaneous trip on the Micrologic 2.0 (NS) trip units in the calculator.
It is modelled as a short-time trip instead. The catalogue refers to the trip as instantaneous.
However, it behaves like a short-time trip when compared to other electronic trip units.
Prospective phase fault:
The prospective phase fault current on the primary side of the circuit breaker.
Specify the 3-phase fault current for "3 Phase AC" supplies. Or specify the phase-to-neutral fault current for "1 Phase AC" and "DC" supplies.
When
Check short circuit rating
is selected, this parameter is used to calculate
the phase fault let-through-energy (I
2
t) of the circuit breaker and compares it against the fault energy rating of the cable.
Prospective earth fault (kA):
The prospective earth fault current on the primary side of the circuit breaker.
Specify the phase-to-earth fault current for "3 Phase AC", "1 Phase AC" and "DC" supplies.
When
Check loop impedance
is selected,
this parameter is also used to calculate the external source loop impedance for earth faults.
When
Check short circuit rating
is selected, it is also used to calculate
the earth fault let-through-energy (I
2
t) of the circuit breaker and compares it against the fault energy rating of the cable.
Short circuit protection parameters -Generic
Current limiting (yes/no):
Specify if the circuit breaker or fuse can limit the fault energy. For example current limiting fuses and MCCBs.
Prospective phase fault current (kA):
The prospective fault current on the primary side of the circuit breaker.
It is used to calculate the phase fault current at the load.
It is used to check the phase fault current rating of the live and neutral cores of the cable if the current limiting option is not selected.
Phase fault let-through energy (A
2
s):
It is checked against the fault energy rating of the live and neutral cores of the cable if the current limiting option is not selected
The let-through energy (I
2
t) is available on current-limiting curves from the device manufacturer.
It is a function of the prospective phase fault current.
Phase fault trip time (ms):
The phase fault clearing time of the protection device.
It is used to check the fault current rating of the live and neutral cores of the cable if the current limiting option is not selected.
Prospective earth fault current (kA):
The prospective phase-to-earth fault current.
It is used to calculate the earth fault current at the load.
It is used to calculate the external earth loop impedance.
It is used to check the earth fault current rating of the live and earth cores of the cable if the current limiting option is not selected.
Earth fault let-through energy (A
2
s):
It is checked against the fault energy rating of the live and earth cores of the cable if the current limiting option is not selected.
The let-through energy (I
2
t) is available on current-limiting curves from the device manufacturer.
It is a function of the prospective earth fault current.
Earth fault trip current (A):
The earth fault trip setting of the protection device.
It is used to check the earth loop impedance of the circuit.
Earth fault trip time (ms):
The earth fault clearing time of the protection device.
It is used to check the earth fault current rating of the live and earth cores of the cable if the current limiting option is not selected.
Cable group definition
A
cable group
refers to a set of single-core cables in a circuit.
For example, red, white, and blue phase single-core cables.
For three-phase applications, A
cable group
includes Three-phase cables, the neutral cable (if applicable), and the earth cable.
It can be installed in a flat or trefoil formation.
For single-phase applications, A
cable group
includes a phase cable, a neutral cable, and an earth cable.
Each set is counted as one separate cable group.
Do not count the three phases.
Do not count the neutral.
Do not count the earth cable.
Example: Two parallel single-core cable groups.
Example: Two parallel multi-core cables.
Cable current rating calculation
The current ratings are selected from Tables 4 to 21 in AS/NZS 3008-2017. It is based on cable type, insulation type and the cable installation method.
For Australian conditions, Tables 4 to 21 are based on an ambient temperature of 40°C and a ground temperature of 25°C.
For New Zealand conditions, Tables 4 to 21 are based on an ambient temperature of 30°C and a ground temperature of 15°C.
The cable sizing calculator supports the following conductors:
Copper (solid, stranded and flexible).
Aluminium (solid, stranded and flexible).
Cable current derating calculation
The current derating for the cables has been implemented according to AS/NZS 3008:2017.
Cable impedance calculation
The impedance is calculated as:
\(Z_c = \sqrt{R_c^2 + X_c^2}\)
Where,
R
c
is the cable
resistance
in Ω/km.
X
c
is the cable
reactance
in Ω/km.
Loop impedance calculation
There are three methods to calculate the maximum loop distance, depending on how the source impedance is determined.
Source impedance
Calculation
Estimated according to AS/NZS 3000.
(MCB protection only)
Max. distance.
\(L_{max}=\dfrac{0.8 \cdot V_{1\phi} \cdot 1000}{I_{min} \cdot (Z_{p} + Z_{e}) }\)
Calculated from prospective earth fault current.
(All protection types).
Max. total loop impedance.
\(Z_{max}= \dfrac{V_{1\phi}} {I_{min}} \)
Source impedance.
\(Z_{s}= \dfrac{ V_{1\phi} } { I_{f} \cdot 1000 } \)
Max. distance.
\( L_{max} = \dfrac {\left( Z_{max} - Z_{s} \right) \cdot 1000 } { Z_{p} + Z_{e} } \)
Measured.
(MCB protection only)
Max. total loop impedance.
\(Z_{max}= \dfrac{V_{1\phi}} {I_{min}} \)
Max. distance.
\( L_{max} = \dfrac {\left( Z_{max} - Z_{s} \right) \cdot 1000 } { Z_{p} + Z_{e} } \)
Where:
V
1Φ
, single-phase-to-earth or DC-to-earth voltage.
I
min
, minimum trip current of protection device.
I
f
, prospective earth fault current.
Z
s
, measured source impedance in Ω.
Z
max
, maximum allowable total loop impedance in Ω.
Z
p
, phase core impedance in Ω/km.
Z
e
, earth core impedance in Ω/km.
L
max
, maximum allowable cable distance in meters.
For parallel cables, the phase core impedance (
Z
p
) is divided by the number of phase cores (
m
), and the earth core impedance (
Z
e
) is divided by the number of earth cores (
n
).
Voltage drop calculation with worst-case load power factor
This is the default method in the calculator.
It is the simplest. The most conservative. And the most often used.
The worst-case power factor is when the cable and load power factors are the same.
The voltage drop formulas are shown below.
1 Phase AC
\(\Delta V_{1\phi}=\dfrac{I \cdot L \cdot 2 \cdot Z_{c}}{1000}\)
3 Phase AC
\(\Delta V_{3\phi}=\dfrac{I \cdot L \cdot \sqrt{3} \cdot Z_{c}}{1000}\)
DC
\(\Delta V_{dc}=\dfrac{I \cdot L \cdot 2 \cdot R_{c\_ph}}{1000}\)
Where,
I
is the load current in ampere (A).
L
is the cable distance in meters (m).
Z
c
is the cable impedance in Ω/km.
R
c
is the cable
resistance
in Ω/km.
The impedance
Z
c
for the worst-case power factor is calculated as:
\(Z_c = \sqrt{R_c^2 + X_c^2}\)
Where,
R
c
is the cable
resistance
in Ω/km.
X
c
is the cable
reactance
in Ω/km.
Voltage drop calculation with specified load power factor
The specified load power factor is used to calculate the voltage drop.
This will result in a lower voltage drop.
It is useful when the power factor of the load is known. And it is stable at full load. For example, electrical motors.
The formulas are shown below.
1 Phase AC
\(\Delta V_{1\phi} {=} \dfrac{I {\cdot} L {\cdot} 2 {\cdot} [R_{c} {\cdot} \cos (\theta) {+} X_{c} {\cdot} \sin (\theta)]}{1000}\)
3 Phase AC
\(\Delta V_{3\phi} {=} \dfrac{I {\cdot} L {\cdot} \sqrt{3} {\cdot} [R_{c} {\cdot} \cos (\theta) {+} X_{c} {\cdot} \sin (\theta)]}{1000}\)
DC
\(\Delta V_{dc}=\dfrac{I \cdot L \cdot 2 \cdot R_{c\_ph}}{1000}\)
Where,
I
is the load current in ampere (A).
L
is the cable distance in meters (m).
R
c
is the cable
resistance
in Ω/km.
X
c
is the cable
reactance
in Ω/km.
θ = arccos(pf)
, and
pf
is the specified load power factor.
Cable resistance
The calculator selects the resistance, R
c
, values from Table 34, Table 35 and Table 37 in AS/NZS 3008.
The selection is based on the "Conductor Temperature" selection under the voltage drop options.
Conductor temperature
Resitance selection
Calculated
The cable resistance is lower at lower conductor temperatures.
The conductor temperature is calculated.
The resistance is selected from the column in the relevant resistance table with the next higher temperature.
This is described in section 4.4. in AS/NZS 3008.
Maximum
The maximum allowable insulation temperature is used.
The resistance is selected from the column in the relevant resistance table with the maximum allowable insulation temperature.
This is the most conservative option.
Table 36 (shaped conductors) is not used. Table 35 (circular conductors) is used instead. It is more conservative.
AS/NZS 3008 does not specify the DC resistance. The specified AC values are used.
Cable reactance
The calculator selects the reactance values, X
c
, from Table 30 and Table 31 in AS/NZS 3008.
Short circuit calculation
The short circuit capacity of the cables is calculated according to AS/NZS 3008-2017 as
\(I^2t = K^2S^2\)
Where:
I
is the short circuit current capacity in amperes,
t
is the short circuit duration in seconds.
S
is the cross-sectional area of the conductor.
K
is a constant that is selected from Table 52 in AS/NZS 3008-2017.
The fault constant,
K
, is based on the insulation material, the initial conductor temperature, and the final conductor temperature.
The calculator uses the maximum allowable operating temperature as the initial conductor temperature. For example, 75°C is used for PVC insulated cables, 90°C is used for XLPE insulated cables, and 110°C is for XLPE 110°C.
The maximum allowable short circuit temperature from Table 53 in AS/NZS 3008-2017 is used as the final conductor temperature i.e. 160°C for PVC and 250°C for XLPE.
The calculator selects the K value from Table 52 in AS/NZS 3008, based on the initial conductor temperature and the maximum allowable short circuit temperature.
Conduit calculation
Conduit size calculations are based on Tables C10, C11 and C12 in AS/NZS 3000:2018
The tables specify the maximum number of cables for a specific cable size, cable type, consuit type and conduit size.
The tables cover only PVC and XLPE insulation. Not elastomer (rubber) insulation.
Table
Cable type
Sizes
C10
a
Single-core cables
1 to 630 mm
2
C11 (circular)
Two-core and earth cables
1.5 to 25 mm
2
C11 (flat)
b
Two-core and earth cables
1 to 16 mm
2
C12
c
Four-core and earth cables
1.5 to 120 mm
2
Note a:
The cable size for single-core cables is based on the largest cable in a cable group. For example, a 3x1C+E single-core group (16 mm
2
actives, 6 mm
2
earth), is calculated as a 4 x 16 mm
2
cables.
Note b:
Flat multi-core cables are not currently supported in jCalc.
Note c:
PVC and XLPE insulated cables are specified separately in Table C12. They have minor differences. jCalc uses the more conservative PVC data for both XLPE and PVC cables.
Tables C10, C11 and C12 covers four conduit types.
Conduit type
Size range
Heavy duty rigid conduit
20 to 150 mm
Corflow
100 to 150 mm
Medium duty corrugated
20 to 40 mm
Medium duty rigid
16 to 50 mm
Here is an example of how the maximum number of cables is specified in Table C12.
Cable size
mm
2
Medium duty corrugated
20mm
25mm
32mm
40mm
1.5
0
1
1
2
2.5
0
0
1
1
4
0
0
1
1
6
0
0
1
1 |
| Markdown | ***
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***
# Cable Size Calculator AS/NZS 3008
Cable size calculator for current rating, voltage drop, loop impedance, earth cable and short circuit, based on Australia and New Zealand standard AS/NZS 3008.
Free version.
Screen capture not allowed for commercial purposes.
Purchase subscription to remove watermark.
WARNING! Are you sure? All inputs in the form will be replaced by default values.
## How can I improve this calculator?
Please click **[here](https://www.jcalc.net/contact)** to let me know.
## Parameters
- [Standard](https://www.jcalc.net/cable-sizing-calculator-as3008#standardHeadingInfo)
- [Load](https://www.jcalc.net/cable-sizing-calculator-as3008#loadHeadingInfo)
- [Voltage drop](https://www.jcalc.net/cable-sizing-calculator-as3008#voltdropHeadingInfo)
- [Active cable](https://www.jcalc.net/cable-sizing-calculator-as3008#cableTypeHeadingInfo)
- [Earth cable](https://www.jcalc.net/cable-sizing-calculator-as3008#earthCableHeadingInfo)
- [Installation](https://www.jcalc.net/cable-sizing-calculator-as3008#installationHeadingInfo)
- [Installation derating](https://www.jcalc.net/cable-sizing-calculator-as3008#installationDeratingHeadingInfo)
- [Short circuit](https://www.jcalc.net/cable-sizing-calculator-as3008#protectionHeadingInfo)
- [MCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCB)
- [MCCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCCB)
- [Generic device](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoGeneric)
## Definitions
- [Single-core cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition)
## Calculations
- [Current rating](https://www.jcalc.net/cable-sizing-calculator-as3008#ratingCalculation)
- [Derating](https://www.jcalc.net/cable-sizing-calculator-as3008#deratingCalculation)
- [Impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#impedanceCalculation)
- [Loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#loopImpedanceCalculation)
- [Voltage drop](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationWorseCase)
- [Worst-case power factor](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationWorseCase)
- [Specified power factor](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationSpecified)
- [Resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance)
- [Reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance)
- [Short circuit](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitCalculation)
- [Conduit](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation)
## See Also
- [Maximum Demand Calculator AS/NZS 3000](https://www.jcalc.net/maximum-demand-calculator-as3000)
- [Arc Flash Calculator IEEE 1584](https://www.jcalc.net/arc-flash-calculator-ieee)
## Standard parameters
- **Standard:** Select the relevant part in AS/NZS 3008: 2017.
- [Part 1:](https://store.standards.org.au/product/as-nzs-3008-1-1-2017) Australian conditions. Air 40°C. Soil 25°C.
- [Part 2:](https://store.standards.org.au/product/as-nzs-3008-1-2-2017) New Zealand conditions. Air 30°C. Soil 15°C.
- The differences between the parts are:
- Rating tables, Table 4 to 15.
- Air temperature derating, Table 27(1).
- Soil temperature derating, Table 27(2).
## Load parameters
- **Phase:** Select the phase arrangement.
| | |
|---|---|
| Three-phase AC 400V, 415V |  Large loads and consumer mains. |
| Single-phase AC 230V, 240V |  Smaller loads and consumer mains. |
| DC 12V, 24V, 110V | |
| Two-phase 120° 400V, 415V |  Occasionally used in industrial and commercial lighting. Occasionally used as residential mains. |
| Two-phase 180° 480V, 460V |  Rural mains and large rural loads on [SWER](https://en.wikipedia.org/wiki/Single-wire_earth_return) systems. |
- **Voltage (V):** Select the voltage. If the voltage is not available in the select list, choose "Other" and specify any value in the ranges shown below.
- **Specify voltage (V):** Specify any voltage in the following ranges.
| | min | max |
|---|---|---|
| Three-phase AC Two-phase 120° Two-phase 180° | 1 V | 1,000 V phase-to-phase |
| Single-phase AC DC | 1 V | 1,000 V phase-to-neutral |
- **Rating:** Specify the load rating in kW, kVA, A, or hp.
When the rating is in ampere, enter the **per‑phase** line current for 3‑phase systems. For example, enter only 100 A in the following scenario.
| | |
|---|---|
| Phase 1 line current | 100 A |
| Phase 2 line current | 100 A |
| Phase 3 line current | 100 A |
| Enter only 100 A | |
Note: It is the line current (not the delta winding current) for three-phase motors.
- **PF:** Specify the load power factor when the load rating is specified in kW or hp. It is also required for A and kVA ratings when the [Load Power Factor](https://www.jcalc.net/cable-sizing-calculator-as3008#loadPowerFactorTypeParameter) option is selected as Specified under [Advanced Voltage Drop](https://www.jcalc.net/cable-sizing-calculator-as3008#showVoltdropOptionsParameter) options.
## Voltage drop parameters
- **Max. volt drop (%):** Select the maximum allowable voltage drop at the load. Select Other to specify a custom value.
- **Specify max. volt drop (%):** Specify any voltage drop between 0.01 % and 100 %.
- **Distance (m):** The cable length in meters from the source to the load. The return length is automatically included by the calculator for single-phase and three-phase installations.
- **Advanced options:** Select to show the following two options.
- **Conductor temperature:** Select Calculate or Maximum.
| | |
|---|---|
| Calculate (default) | The calculated operating temperature is used to select the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) for voltage drop calculations. Read more [here](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance). |
| Maximum | The maximum rated temperature of the insulation is used to select the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) for voltage drop calculations. This is the most conservative option. |
- **Load power factor:** Worst-case or Specified.
| | |
|---|---|
| Worst case (default) | The worst-case power factor is used to calculate the voltage drop. This is the most conservative option. Read more [here](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationWorseCase). |
| Specified | The specified power factor of the load is used to calculate the voltage drop. Read more [here](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationSpecified). |
## Active cable parameters
- **Insulation:** Select the insulation for the cables. For multi-core cables, this applies to the live, neutral, and earth conductors. For single-core cables, this applies to the live and neutral conductors. The earth cable is selected under [Earth Cable Insulation](https://www.jcalc.net/cable-sizing-calculator-as3008#earthInsulationInfo).
| PVC | Max. operating temp. | |
|---|---|---|
| V-90 | Standard. Most popular insulation. May be operated at 90°C temporarily, with no mechanical pressure on the insulation. | 75°C |
| V-90HT | High temperature. May be operated at 105°C temporarily, with no mechanical pressure on the insulation. | 75°C |
| V-75 | Traditional (older) type PVC cables. | 75°C |
| XLPE | | |
| X-90 | Standard. Most popular XLPE insulation. | 90°C |
| X-HF-90 | Fire rated. | 90°C |
| X-110 | High temperature. | 110°C |
| X-HF-110 | High temperature. Fire rated. | 110°C |
| Elastomer (rubber) | | |
| R-EP-90 | Standard. | 90°C |
| R-HF-90 | Fire rated. | 90°C |
| R-E-110 | High temperature. | 110°C |
| R-HF-110 | High temperature. Fire rated. | 110°C |
- **Cable type:** Select the cable type as shown below.
| 1 Phase AC or DC | |
|---|---|
| **Multi-core 2C+E** One live core. One neutral core. One earth core. |  |
| **Multi-core 2C (mains)** One live core. One combined earth and neutral core. |  |
| **Single-cores 2x1C+E** One live cable. One neutral cable. One earth cable. |  |
| **Single-cores 2x1C (mains)** One live cable. One combined earth and neutral cable. |  |
| 3 Phase AC | |
| **Multi-core 3C+E** Three-phase cores. One earth core. |  |
| **Multi-core 4C+E** Three-phase cores. One neutral core. One earth core. |  |
| **Multi-core 4C (mains)** Three-phase cores. One combined earth and neutral core. |  |
| **Single-cores 3x1C+E** Three-phase cables. One earth cable. |  |
| **Single-cores 4x1C+E** Three-phase cables. One neutral cable. One earth cable. |  |
| **Single-cores 4x1C (mains)** Three-phase cables. One combined earth and neutral core. |  |
- **Flexible:** Select if a flexible cable is used.
- **Conductor:** Select Copper or Aluminium.
- **Active size (mm2):** Select a conductor size or select Auto. The Auto option will automatically select the smallest cable that meets the following criteria.
- Current rating.
- Voltage drop.
- Fault current rating.
- Loop impedance.
- Protection device thermal trip current.
This applies to the live and neutral conductors.
- **Use parallel cables (or cable groups):** Enables the use of parallel mutli-core cables, or parallel single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) in a circuit for high-current installations. This means more than one one live core per phase. The minimum allowable size for parallel cables is 4 mm2, as specified in AS/NZS 3000.
Parallel cables are not supported for "Exposed to Sun" installations by AS/NZS 3008.
- **Number of parallel cables (or cable groups):** The number of parallel multi-core cables or parallel single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) in this circuit.
This is when you want to use parallel multi-core cables or single-core cable groups in a circuit to increase the current rating or reduce the voltage drop.
For single-core cables, the whole [cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) is counted as one. The [cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) includes the three-phase cables, the neutral cable, and the earth cable. It can be installed in a flat or trefoil formation.
Parallel cables are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Examples:
Three parallel multi-core cables
Three parallel single-core cable groups
## Earth cable parameters
- **Earth cable insulation:** Applicable to single-core cables. It can be different from the active cable insulation. The options are the same as the [active cable insulation options.](https://www.jcalc.net/cable-sizing-calculator-as3008#insulationInfo)
- **Flexible earth:** Applicable to single-core cables. Select if a flexible earth cable is used.
- **Earth conductor:** Applicable to single-core cables. Select Copper or Aluminium. Note that you cannot select Aluminium for a copper active cable. Please let me know if you need to.
- **Earth core size (mm2):** Select an earth cable size or select Auto.
### Multi-core cables
Only Auto is supported for multi-core cables.
The calculator will select the minimum copper earth size from [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) in AS/NZS 3000. These sizes match commercial copper multi-core cables.
For aluminium cables the calculator will select an earth size equal to the active size. This matches most commercial aluminium cables.
The fault current rating and loop impedance requirements are checked if [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled. It does not increase the earth size.
### Parallel multi-core cables
The earth fault rating is checked per earth core, i.e. no earth fault current split is considered.
The loop impedenace is checked on the combination of parallel active and earth cores, i.e. an equal earth fault current split is considered.
### Single-core cables
Single-core cables support Auto and Manual selection of the earth size.
To select a specific earth size, select a specific active size first.
In Auto, the selection process is as follows:
- Step 1: The calculator begins with the minimum recommended earth size [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) in AS/NZS 3000.
- Step 2: If [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled, the calculator increases the earth cable size until both the fault current rating and loop impedance requirements are met.
- Step 3: If no suitable earth size is found, the active size is used. If you need a larger earth cable, select it manually.
If the earth core size is selected manually, the selected earth size is still checked against [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000). The fault rating and earth loop impedance are also checked when these options are selected.
[Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) does not specify aluminium earth sizes. They are calculated based on the impedance and fault rating of the equivalent copper earth cables. Click [here](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) for more details.
### Parallel single-core cables
By default, the earth fault rating is checked per earth cable, i.e. no earth fault current split is considered.
However, in high current installations, the option [Combined fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#allowEarthFaultCurrentSplitInfo) can be enabled, and earth fault rating will be based on an equal split of fault current across parallel earth cables. See [Combined fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#allowEarthFaultCurrentSplitInfo) for more information.
The loop impedance is checked on the combination of parallel active and earth cables, i.e. an equal earth fault current split is considered.
For parallel active and parallel earth cables, the combined active size is calculated as:
\\(S\_{active\\\_combined} = \\dfrac {S\_{active} \\cdot m}{n} \\)
Where,
- **Sactive** is the size of one of the active cables in mm2.
- **m** is the number of parallel phase cables.
- **n** is the number of parallel earth cables.
The combined active size is then used to select the minimum earth size from [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000).
For multiple earth cables, the calculator checks that each earth cable is equal to or larger than the minimum earth cable required for one individual active conductor.
For example, in [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) the minimum earth cable size for a 240 mm2 active cable is 95 mm2. If two earth cables are selected, the minimum individual earth cable size is still 95 mm2.
If the combined active size is larger than 630 mm2, the earth size is calculated according to [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) as follows:
- Copper: Minimum 25% of the combined active size.
- Aluminium: Minimum 40% of the combined active size.
For high current installations, the option [Ignore table 5.1](https://www.jcalc.net/cable-sizing-calculator-as3008#ignoreTable51Info) can be enabled, and [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) will be enforced up to 120 mm2 (copper) or 240 mm2 (aluminium) only. See [Ignore table 5.1](https://www.jcalc.net/cable-sizing-calculator-as3008#ignoreTable51Info) for more information.
- **Number of earth cores or cables:**
| | |
|---|---|
| Multi-core cables | Matches the number of parallel cables. Cannot be changed. |
| One single-core [cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) | One or two earth cables. |
| Multiple single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) | Any number of earth cables between one and the number of parallel cable groups. |
- **Advanced options:** Select to show the following two options.
- **Ignore table 5.1 sizes:** Ignores earth sizes specified in [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) in AS/NZS 3000. Earth size will be based on earth fault current and loop impedance only.
This allows for more economical earth cable sizes.
This option is only available for:
- Three-phase, single-core cables, excluding mains.
- Number of parallel cable groups \> 1.
- [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled.
- The calculated earth size is ≥ 120 mm2 (copper) or ≥ 240 mm2 (aluminium).
- **Combined earth fault rating:** The fault rating of the earth cables is based on an equal split of earth fault current across the parallel earth cables.
This allows for more economical earth cable sizes.
This option is only available for:
- Three-phase, single-core cables, excluding mains.
- Number of parallel cable groups \> 1.
- Number of parallel earth cables \> 1.
- [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled.
- The calculated earth size is ≥ 120 mm2 (copper) or ≥ 240 mm2 (aluminium).
**Important:** To ensure safety, it is essential that the parallel earth cables:
- are the same length,
- follow the same route,
- are mechanically protected,
- insulated,
- and separated from the live cables to prevent direct faults between phase and earth cables.
## Installation parameters
- **Formation:** Trefoil or laid flat.
- **Installation method:** Select the installation method. Consider the worst-case section of the cable installation. Which is the installation section with the lowest current rating.
## Installation derating parameters
- **Show derating options:** Check this box if you want to specify derating options. If not, the following default derating options are used.
| | Australian conditions | New Zealand conditions |
|---|---|---|
| Number of cables or cable groups | 1 | 1 |
| Air temperature | 40 °C | 30 °C |
| Soil temperature | 25 °C | 15 °C |
| Cable depth | 0\.5 m | 0\.5 m |
| Soil resistivity | 1\.2 °C.m/W | 1\.2 °C.m/W |
| Circuit derating | None | None |
- **Cable support:** The cable support options depend on the installation method.
- **Number of cables (or cable groups):** The number of multi-core cables or single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) in this installation. This includes parallel cables in this circuit and cables from any other circuits included in the same installation.
The standard refers to this parameter as the Number of Circuits. And the standard treats parallel cables as multiple circuits. jCalc uses the names "Number of cables" and "Number of cable groups" instead of "Number of Circuits" to make it more intuitive, especially when parallel cables are used.
Note that the parameter [number of parallel cables (or cable groups)](https://www.jcalc.net/cable-sizing-calculator-as3008#numberOfCablesInfo) under Cable Type specifies the number of parallel cables in this circuit only. This parameter considers the parallel cables in this circuit, and cables from any other circuits in the same installation.
All cables in the installation must be considered, because heat from adjacent cables affects the current rating and voltage drop.
For multi-core cables, each cable is considered in the derating. For single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition), each cable group is considered in the derating -not the individual cables for each phase, the neutral or the earth.
Multiple cables (or cable-groups) are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Examples:
Multi-core (number of cables = 3)
Single-core (number of [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) = 3)
- **Space between cables, cable groups or enclosures:** Select the spacing between multi-core cables, single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) or enclosures (underground multi- and single-core). The table below shows the spacing that can be selected for different installations and cable types.
| In air, multi-core cables | |
|---|---|
| Space between the edges of cables. | |
| Touching |  |
| Spaced 1D | The diameter of the largest cable.  |
| In air, single-core cables | |
| Space between the edges of [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition). | |
| Touching |  |
| Spaced 1D | The diameter of the largest cable.  |
| Underground, multi-core cables | |
| Space between the centres of cables. | |
| Touching | Buried direct  Underground enclosure  |
| 150 mm | |
| 300 mm | |
| 450 mm | |
| 600 m | |
| Underground, single-core cables | |
| Space between the centres of [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition). | |
| Touching | Buried direct  Underground enclosure  |
| 150 mm | |
| 300 mm | |
| 450 mm | |
| 600 m | |
- **Number of tiers:** Number of tiers.
- **No of horizontally tiered racks:** The number of horizontal tiers (rows) of racks or ladders installed above each other. The minimum vertical space between racks is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
- **No of horizontally tiered unperforated trays:** The number of horizontal tiers (rows) of trays installed above each other. The minimum vertical space between trays is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
- **No of horizontally tiered perforated trays:** The number of horizontal tiers (rows) of trays installed above each other. The minimum vertical space between trays is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
- **No of vertical back-to-back perforated trays:** On or two vertical back-to-back trays. The minimum vertical space between trays is 230mm. ee AS/NZS 3008:2017 Tables 23 and 24.
- **Air temperature (°C):** For cables installed in air. The defaults (no derating) are.
- Australian conditions: 40°C
- New Zealand conditions: 30°C
- **Soil temperature (°C):** For cables installed underground. The defaults (no derating) are:
- Australian conditions: 25°C
- New Zealand conditions: 15°C
- **Cable depth (m):** The default (no derating) is 0.5 m.
- **Soil resistivity (°C.m/W):** The default (no derating) is 1.2 °C.m/W.
## Conduit parameters
- **Calculate conduit:** Check this box if you want to calculate conduit sizing. The option will only show for installations with enclosures. Conduit sizing is based on Tables C10, C11 and C12 in AS/NZS 3000:2018. Click [here](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation) for more details.
- **Conduit type:** Select the conduit type. Click [here](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation) for more details.
- **Conduit size (mm):** Select a conduit size or select Auto. Click [here](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation) for more details.
## Short circuit protection parameters
- **Check short circuit rating:** Select to check the fault rating of the cable.
- **Check loop impedance:** Select to check the earth loop impedance of the circuit. In other words, check if the specified protection device will trip for an earth fault when the specified cable is used.
The external source impedance is estimated, calculated, or specified (measured). The method depends on the selected [protection device](https://www.jcalc.net/cable-sizing-calculator-as3008#protectionInfo). When it is calculated, it is calculated from the prospective earth fault current.
| Protection device | Loop impedance method |
|---|---|
| [MCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCB) | Estimated, Calculated or Measured |
| [MCCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCCB) | Calculated |
| [Generic device](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoGeneric) | Calculated |
- **Protection:** Select the protection device. MCB, MCCB, or Generic.
| Protection device | Description |
|---|---|
| [MCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCB) | Miniature circuit breakers. From 1 A to 125 A. |
| [MCCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCCB) | Moulded case circuit breakers. From 16 A to 3200 A. |
| [Generic device](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoGeneric) | Generic phase and earth current fault protection. With definite time settings. |
## Short circuit protection parameters -MCB
- **MCB curve type:** The MCB tripping curve: B, C or D.
MCBs are manufactured according to AS/NZS 60898.1, which specifies trip current ranges for the MCB curve types.
Calculations in AS/NZS 3000 and jCalc is based on the mean values of the ranges.
| Curve type | Trip current AS/NZS 60898.1 | Trip current AS/NZS 3000 and jCalc |
|---|---|---|
| B | 3-5 x rated current | 4 x rated current |
| C | 5-10 x rated current | 7\.5 x rated current |
| D | 10-20 x rated current | 12\.5 x rated current |
- **MCB rating:** Select an MCB rating or select Auto. The auto option will automatically select the recommended size from Tables C6 and C7 in AS/NZS 3000-2018. In Auto, the MCB size is selected for the load current. And then checked against the cable.
- **Source impedance:** Specify the method to determine the source (external) loop impedance.
- **Estimate:** Estimate according to AS/NZS 3000-2018, i.e. assume that 80% voltage is available at the cable source during an earth fault.
- **Calculate:** Calculate from the prospective fault current.
- **Measured:** Specify the measured impedance in Ohm.
- **Prospective earth fault current (kA):** Specify the prospective earth fault current on the primary side of the circuit breaker. This parameter is required when the [source impedance method](https://www.jcalc.net/cable-sizing-calculator-as3008#sourceImpedanceTypeInfo) is selected as "Calculate". It is used to calculate the external source loop impedance for earth faults.
## Short circuit protection parameters -MCCB
- **Make:** Select between Schneider and Terasaki TemBreak Pro.
- **Model:** Select the model. Note that the number in the model name represents the current rating of the circuit breaker. For example, a Schneider NXS100 is rated for 100A, and a Terasaki P250 for 250A.
- **CB fault rating:** The fault current rating of the circuit breaker. This affects the let-though energy.
- **Trip unit:** Select between Thermal Magnetic, Micrologic 2.3 (NSX) or Micrologic 2.0. (NS)
- **Thermal-magnetic**
- **Trip unit rating:** Select the current rating or select Auto. The following are automatically selected in Auto: trip unit rating, thermal trip setting, and magnetic trip setting. The trip unit rating, and the thermal trip setting, are selected to be ≥ the load current.
- **Thermal trip:** The thermal trip setting can be selected if the trip unit rating is selected manually.
- **Magnetic trip:** The magnetic trip setting can be selected if the trip unit rating is selected manually.
- **Micrologic 2.3 (NSX) and Micrologic 2.0 (NS)**
- **Trip unit rating:** Select the current rating or select Auto. The following are automatically selected in Auto: trip unit rating, thermal trip setting, short-time trip setting, and instantaneous trip setting. The trip unit rating, and the thermal trip setting, are selected to be ≥ the load current. The short-time trip setting is selected as 6x the thermal trip setting.
- **Thermal trip:** The thermal trip setting can be selected if the trip unit rating is selected manually.
- **Short-time trip:** The short-time trip setting can be selected if the trip unit rating is selected manually.
- **Instantaneous trip:** The instantaneous trip setting can be selected if the trip unit rating is selected manually. Note that there is no instantaneous trip on the Micrologic 2.0 (NS) trip units in the calculator. It is modelled as a short-time trip instead. The catalogue refers to the trip as instantaneous. However, it behaves like a short-time trip when compared to other electronic trip units.
- **Prospective phase fault:** The prospective phase fault current on the primary side of the circuit breaker. Specify the 3-phase fault current for "3 Phase AC" supplies. Or specify the phase-to-neutral fault current for "1 Phase AC" and "DC" supplies. When [Check short circuit rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) is selected, this parameter is used to calculate the phase fault let-through-energy (I2t) of the circuit breaker and compares it against the fault energy rating of the cable.
- **Prospective earth fault (kA):** The prospective earth fault current on the primary side of the circuit breaker. Specify the phase-to-earth fault current for "3 Phase AC", "1 Phase AC" and "DC" supplies. When [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) is selected, this parameter is also used to calculate the external source loop impedance for earth faults. When [Check short circuit rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) is selected, it is also used to calculate the earth fault let-through-energy (I2t) of the circuit breaker and compares it against the fault energy rating of the cable.
## Short circuit protection parameters -Generic
- **Current limiting (yes/no):** Specify if the circuit breaker or fuse can limit the fault energy. For example current limiting fuses and MCCBs.
- **Prospective phase fault current (kA):** The prospective fault current on the primary side of the circuit breaker. It is used to calculate the phase fault current at the load. It is used to check the phase fault current rating of the live and neutral cores of the cable if the current limiting option is not selected.
- **Phase fault let-through energy (A2s):** It is checked against the fault energy rating of the live and neutral cores of the cable if the current limiting option is not selected The let-through energy (I2t) is available on current-limiting curves from the device manufacturer. It is a function of the prospective phase fault current.
- **Phase fault trip time (ms):** The phase fault clearing time of the protection device. It is used to check the fault current rating of the live and neutral cores of the cable if the current limiting option is not selected.
- **Prospective earth fault current (kA):** The prospective phase-to-earth fault current. It is used to calculate the earth fault current at the load. It is used to calculate the external earth loop impedance. It is used to check the earth fault current rating of the live and earth cores of the cable if the current limiting option is not selected.
- **Earth fault let-through energy (A2s):** It is checked against the fault energy rating of the live and earth cores of the cable if the current limiting option is not selected. The let-through energy (I2t) is available on current-limiting curves from the device manufacturer. It is a function of the prospective earth fault current.
- **Earth fault trip current (A):** The earth fault trip setting of the protection device. It is used to check the earth loop impedance of the circuit.
- **Earth fault trip time (ms):** The earth fault clearing time of the protection device. It is used to check the earth fault current rating of the live and earth cores of the cable if the current limiting option is not selected.
## Cable group definition
A **cable group** refers to a set of single-core cables in a circuit. For example, red, white, and blue phase single-core cables.
For three-phase applications, A **cable group** includes Three-phase cables, the neutral cable (if applicable), and the earth cable. It can be installed in a flat or trefoil formation.
For single-phase applications, A **cable group** includes a phase cable, a neutral cable, and an earth cable.
Each set is counted as one separate cable group.
- Do not count the three phases.
- Do not count the neutral.
- Do not count the earth cable.
Example: Two parallel single-core cable groups.
Example: Two parallel multi-core cables.
## Cable current rating calculation
The current ratings are selected from Tables 4 to 21 in AS/NZS 3008-2017. It is based on cable type, insulation type and the cable installation method.
For Australian conditions, Tables 4 to 21 are based on an ambient temperature of 40°C and a ground temperature of 25°C.
For New Zealand conditions, Tables 4 to 21 are based on an ambient temperature of 30°C and a ground temperature of 15°C.
The cable sizing calculator supports the following conductors:
- Copper (solid, stranded and flexible).
- Aluminium (solid, stranded and flexible).
## Cable current derating calculation
The current derating for the cables has been implemented according to AS/NZS 3008:2017.
## Cable impedance calculation
The impedance is calculated as:
\\(Z\_c = \\sqrt{R\_c^2 + X\_c^2}\\)
Where,
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
- **Xc** is the cable [reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance) in Ω/km.
## Loop impedance calculation
There are three methods to calculate the maximum loop distance, depending on how the source impedance is determined.
| Source impedance | Calculation |
|---|---|
| Estimated according to AS/NZS 3000. (MCB protection only) | Max. distance. \\(L\_{max}=\\dfrac{0.8 \\cdot V\_{1\\phi} \\cdot 1000}{I\_{min} \\cdot (Z\_{p} + Z\_{e}) }\\) |
| Calculated from prospective earth fault current. (All protection types). | Max. total loop impedance. \\(Z\_{max}= \\dfrac{V\_{1\\phi}} {I\_{min}} \\) Source impedance. \\(Z\_{s}= \\dfrac{ V\_{1\\phi} } { I\_{f} \\cdot 1000 } \\) Max. distance. \\( L\_{max} = \\dfrac {\\left( Z\_{max} - Z\_{s} \\right) \\cdot 1000 } { Z\_{p} + Z\_{e} } \\) |
| Measured. (MCB protection only) | Max. total loop impedance. \\(Z\_{max}= \\dfrac{V\_{1\\phi}} {I\_{min}} \\) Max. distance. \\( L\_{max} = \\dfrac {\\left( Z\_{max} - Z\_{s} \\right) \\cdot 1000 } { Z\_{p} + Z\_{e} } \\) |
Where:
- **V1Φ**, single-phase-to-earth or DC-to-earth voltage.
- **Imin**, minimum trip current of protection device.
- **If**, prospective earth fault current.
- **Zs**, measured source impedance in Ω.
- **Zmax**, maximum allowable total loop impedance in Ω.
- **Zp**, phase core impedance in Ω/km.
- **Ze**, earth core impedance in Ω/km.
- **Lmax**, maximum allowable cable distance in meters.
For parallel cables, the phase core impedance (**Zp**) is divided by the number of phase cores (**m**), and the earth core impedance (**Ze**) is divided by the number of earth cores (**n**).
## Voltage drop calculation with worst-case load power factor
This is the default method in the calculator.
It is the simplest. The most conservative. And the most often used.
The worst-case power factor is when the cable and load power factors are the same.
The voltage drop formulas are shown below.
| | |
|---|---|
| 1 Phase AC | \\(\\Delta V\_{1\\phi}=\\dfrac{I \\cdot L \\cdot 2 \\cdot Z\_{c}}{1000}\\) |
| 3 Phase AC | \\(\\Delta V\_{3\\phi}=\\dfrac{I \\cdot L \\cdot \\sqrt{3} \\cdot Z\_{c}}{1000}\\) |
| DC | \\(\\Delta V\_{dc}=\\dfrac{I \\cdot L \\cdot 2 \\cdot R\_{c\\\_ph}}{1000}\\) |
Where,
- **I** is the load current in ampere (A).
- **L** is the cable distance in meters (m).
- **Zc** is the cable impedance in Ω/km.
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
The impedance **Zc** for the worst-case power factor is calculated as:
\\(Z\_c = \\sqrt{R\_c^2 + X\_c^2}\\)
Where,
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
- **Xc** is the cable [reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance) in Ω/km.
## Voltage drop calculation with specified load power factor
The specified load power factor is used to calculate the voltage drop.
This will result in a lower voltage drop.
It is useful when the power factor of the load is known. And it is stable at full load. For example, electrical motors.
The formulas are shown below.
| | |
|---|---|
| 1 Phase AC | \\(\\Delta V\_{1\\phi} {=} \\dfrac{I {\\cdot} L {\\cdot} 2 {\\cdot} \[R\_{c} {\\cdot} \\cos (\\theta) {+} X\_{c} {\\cdot} \\sin (\\theta)\]}{1000}\\) |
| 3 Phase AC | \\(\\Delta V\_{3\\phi} {=} \\dfrac{I {\\cdot} L {\\cdot} \\sqrt{3} {\\cdot} \[R\_{c} {\\cdot} \\cos (\\theta) {+} X\_{c} {\\cdot} \\sin (\\theta)\]}{1000}\\) |
| DC | \\(\\Delta V\_{dc}=\\dfrac{I \\cdot L \\cdot 2 \\cdot R\_{c\\\_ph}}{1000}\\) |
Where,
- **I** is the load current in ampere (A).
- **L** is the cable distance in meters (m).
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
- **Xc** is the cable [reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance) in Ω/km.
- **θ = arccos(pf)**, and **pf** is the specified load power factor.
## Cable resistance
The calculator selects the resistance, Rc, values from Table 34, Table 35 and Table 37 in AS/NZS 3008.
The selection is based on the "Conductor Temperature" selection under the voltage drop options.
| Conductor temperature | Resitance selection |
|---|---|
| Calculated | The cable resistance is lower at lower conductor temperatures. The conductor temperature is calculated. The resistance is selected from the column in the relevant resistance table with the next higher temperature. This is described in section 4.4. in AS/NZS 3008. |
| Maximum | The maximum allowable insulation temperature is used. The resistance is selected from the column in the relevant resistance table with the maximum allowable insulation temperature. This is the most conservative option. |
Table 36 (shaped conductors) is not used. Table 35 (circular conductors) is used instead. It is more conservative.
AS/NZS 3008 does not specify the DC resistance. The specified AC values are used.
## Cable reactance
The calculator selects the reactance values, Xc, from Table 30 and Table 31 in AS/NZS 3008.
## Short circuit calculation
The short circuit capacity of the cables is calculated according to AS/NZS 3008-2017 as
\\(I^2t = K^2S^2\\)
Where:
- **I** is the short circuit current capacity in amperes,
- **t** is the short circuit duration in seconds.
- **S** is the cross-sectional area of the conductor.
- **K** is a constant that is selected from Table 52 in AS/NZS 3008-2017.
The fault constant, **K**, is based on the insulation material, the initial conductor temperature, and the final conductor temperature.
The calculator uses the maximum allowable operating temperature as the initial conductor temperature. For example, 75°C is used for PVC insulated cables, 90°C is used for XLPE insulated cables, and 110°C is for XLPE 110°C.
The maximum allowable short circuit temperature from Table 53 in AS/NZS 3008-2017 is used as the final conductor temperature i.e. 160°C for PVC and 250°C for XLPE.
The calculator selects the K value from Table 52 in AS/NZS 3008, based on the initial conductor temperature and the maximum allowable short circuit temperature.
## Conduit calculation
Conduit size calculations are based on Tables C10, C11 and C12 in AS/NZS 3000:2018
The tables specify the maximum number of cables for a specific cable size, cable type, consuit type and conduit size.
The tables cover only PVC and XLPE insulation. Not elastomer (rubber) insulation.
| Table | Cable type | Sizes |
|---|---|---|
| C10**a** | Single-core cables | 1 to 630 mm2 |
| C11 (circular) | Two-core and earth cables | 1\.5 to 25 mm2 |
| C11 (flat)**b** | Two-core and earth cables | 1 to 16 mm2 |
| C12**c** | Four-core and earth cables | 1\.5 to 120 mm2 |
- **Note a:** The cable size for single-core cables is based on the largest cable in a cable group. For example, a 3x1C+E single-core group (16 mm2 actives, 6 mm2 earth), is calculated as a 4 x 16 mm2 cables.
- **Note b:** Flat multi-core cables are not currently supported in jCalc.
- **Note c:** PVC and XLPE insulated cables are specified separately in Table C12. They have minor differences. jCalc uses the more conservative PVC data for both XLPE and PVC cables.
Tables C10, C11 and C12 covers four conduit types.
| Conduit type | Size range |
|---|---|
| Heavy duty rigid conduit | 20 to 150 mm |
| Corflow | 100 to 150 mm |
| Medium duty corrugated | 20 to 40 mm |
| Medium duty rigid | 16 to 50 mm |
Here is an example of how the maximum number of cables is specified in Table C12.
| Cable size mm2 | Medium duty corrugated | | | |
|---|---|---|---|---|
| 20mm | 25mm | 32mm | 40mm | |
| 1\.5 | 0 | 1 | 1 | 2 |
| 2\.5 | 0 | 0 | 1 | 1 |
| 4 | 0 | 0 | 1 | 1 |
| 6 | 0 | 0 | 1 | 1 |
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| Readable Markdown | ## See Also
- [Maximum Demand Calculator AS/NZS 3000](https://www.jcalc.net/maximum-demand-calculator-as3000)
- [Arc Flash Calculator IEEE 1584](https://www.jcalc.net/arc-flash-calculator-ieee)
## Standard parameters
- **Standard:** Select the relevant part in AS/NZS 3008: 2017.
- [Part 1:](https://store.standards.org.au/product/as-nzs-3008-1-1-2017) Australian conditions. Air 40°C. Soil 25°C.
- [Part 2:](https://store.standards.org.au/product/as-nzs-3008-1-2-2017) New Zealand conditions. Air 30°C. Soil 15°C.
- The differences between the parts are:
- Rating tables, Table 4 to 15.
- Air temperature derating, Table 27(1).
- Soil temperature derating, Table 27(2).
## Load parameters
- **Phase:** Select the phase arrangement.
- **Voltage (V):** Select the voltage. If the voltage is not available in the select list, choose "Other" and specify any value in the ranges shown below.
- **Specify voltage (V):** Specify any voltage in the following ranges.
| | min | max |
|---|---|---|
| Three-phase AC Two-phase 120° Two-phase 180° | 1 V | 1,000 V phase-to-phase |
| Single-phase AC DC | 1 V | 1,000 V phase-to-neutral |
- **Rating:** Specify the load rating in kW, kVA, A, or hp.
When the rating is in ampere, enter the **per‑phase** line current for 3‑phase systems. For example, enter only 100 A in the following scenario.
| | |
|---|---|
| Phase 1 line current | 100 A |
| Phase 2 line current | 100 A |
| Phase 3 line current | 100 A |
| Enter only 100 A | |
Note: It is the line current (not the delta winding current) for three-phase motors.
- **PF:** Specify the load power factor when the load rating is specified in kW or hp. It is also required for A and kVA ratings when the [Load Power Factor](https://www.jcalc.net/cable-sizing-calculator-as3008#loadPowerFactorTypeParameter) option is selected as Specified under [Advanced Voltage Drop](https://www.jcalc.net/cable-sizing-calculator-as3008#showVoltdropOptionsParameter) options.
## Voltage drop parameters
- **Max. volt drop (%):** Select the maximum allowable voltage drop at the load. Select Other to specify a custom value.
- **Specify max. volt drop (%):** Specify any voltage drop between 0.01 % and 100 %.
- **Distance (m):** The cable length in meters from the source to the load. The return length is automatically included by the calculator for single-phase and three-phase installations.
- **Advanced options:** Select to show the following two options.
- **Conductor temperature:** Select Calculate or Maximum.
| | |
|---|---|
| Calculate (default) | The calculated operating temperature is used to select the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) for voltage drop calculations. Read more [here](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance). |
| Maximum | The maximum rated temperature of the insulation is used to select the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) for voltage drop calculations. This is the most conservative option. |
- **Load power factor:** Worst-case or Specified.
| | |
|---|---|
| Worst case (default) | The worst-case power factor is used to calculate the voltage drop. This is the most conservative option. Read more [here](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationWorseCase). |
| Specified | The specified power factor of the load is used to calculate the voltage drop. Read more [here](https://www.jcalc.net/cable-sizing-calculator-as3008#voltageDropCalculationSpecified). |
## Active cable parameters
- **Insulation:** Select the insulation for the cables. For multi-core cables, this applies to the live, neutral, and earth conductors. For single-core cables, this applies to the live and neutral conductors. The earth cable is selected under [Earth Cable Insulation](https://www.jcalc.net/cable-sizing-calculator-as3008#earthInsulationInfo).
| PVC | Max. operating temp. | |
|---|---|---|
| V-90 | Standard. Most popular insulation. May be operated at 90°C temporarily, with no mechanical pressure on the insulation. | 75°C |
| V-90HT | High temperature. May be operated at 105°C temporarily, with no mechanical pressure on the insulation. | 75°C |
| V-75 | Traditional (older) type PVC cables. | 75°C |
| XLPE | | |
| X-90 | Standard. Most popular XLPE insulation. | 90°C |
| X-HF-90 | Fire rated. | 90°C |
| X-110 | High temperature. | 110°C |
| X-HF-110 | High temperature. Fire rated. | 110°C |
| Elastomer (rubber) | | |
| R-EP-90 | Standard. | 90°C |
| R-HF-90 | Fire rated. | 90°C |
| R-E-110 | High temperature. | 110°C |
| R-HF-110 | High temperature. Fire rated. | 110°C |
- **Cable type:** Select the cable type as shown below.
| 1 Phase AC or DC | |
|---|---|
| **Multi-core 2C+E** One live core. One neutral core. One earth core. |  |
| **Multi-core 2C (mains)** One live core. One combined earth and neutral core. |  |
| **Single-cores 2x1C+E** One live cable. One neutral cable. One earth cable. |  |
| **Single-cores 2x1C (mains)** One live cable. One combined earth and neutral cable. |  |
| 3 Phase AC | |
| **Multi-core 3C+E** Three-phase cores. One earth core. |  |
| **Multi-core 4C+E** Three-phase cores. One neutral core. One earth core. |  |
| **Multi-core 4C (mains)** Three-phase cores. One combined earth and neutral core. |  |
| **Single-cores 3x1C+E** Three-phase cables. One earth cable. |  |
| **Single-cores 4x1C+E** Three-phase cables. One neutral cable. One earth cable. |  |
| **Single-cores 4x1C (mains)** Three-phase cables. One combined earth and neutral core. |  |
- **Flexible:** Select if a flexible cable is used.
- **Conductor:** Select Copper or Aluminium.
- **Active size (mm2):** Select a conductor size or select Auto. The Auto option will automatically select the smallest cable that meets the following criteria.
- Current rating.
- Voltage drop.
- Fault current rating.
- Loop impedance.
- Protection device thermal trip current.
This applies to the live and neutral conductors.
- **Use parallel cables (or cable groups):** Enables the use of parallel mutli-core cables, or parallel single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) in a circuit for high-current installations. This means more than one one live core per phase. The minimum allowable size for parallel cables is 4 mm2, as specified in AS/NZS 3000.
Parallel cables are not supported for "Exposed to Sun" installations by AS/NZS 3008.
- **Number of parallel cables (or cable groups):** The number of parallel multi-core cables or parallel single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) in this circuit.
This is when you want to use parallel multi-core cables or single-core cable groups in a circuit to increase the current rating or reduce the voltage drop.
For single-core cables, the whole [cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) is counted as one. The [cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) includes the three-phase cables, the neutral cable, and the earth cable. It can be installed in a flat or trefoil formation.
Parallel cables are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Examples:
Three parallel multi-core cables
Three parallel single-core cable groups
## Earth cable parameters
- **Earth cable insulation:** Applicable to single-core cables. It can be different from the active cable insulation. The options are the same as the [active cable insulation options.](https://www.jcalc.net/cable-sizing-calculator-as3008#insulationInfo)
- **Flexible earth:** Applicable to single-core cables. Select if a flexible earth cable is used.
- **Earth conductor:** Applicable to single-core cables. Select Copper or Aluminium. Note that you cannot select Aluminium for a copper active cable. Please let me know if you need to.
- **Earth core size (mm2):** Select an earth cable size or select Auto.
### Multi-core cables
Only Auto is supported for multi-core cables.
The calculator will select the minimum copper earth size from [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) in AS/NZS 3000. These sizes match commercial copper multi-core cables.
For aluminium cables the calculator will select an earth size equal to the active size. This matches most commercial aluminium cables.
The fault current rating and loop impedance requirements are checked if [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled. It does not increase the earth size.
### Parallel multi-core cables
The earth fault rating is checked per earth core, i.e. no earth fault current split is considered.
The loop impedenace is checked on the combination of parallel active and earth cores, i.e. an equal earth fault current split is considered.
### Single-core cables
Single-core cables support Auto and Manual selection of the earth size.
To select a specific earth size, select a specific active size first.
In Auto, the selection process is as follows:
- Step 1: The calculator begins with the minimum recommended earth size [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) in AS/NZS 3000.
- Step 2: If [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled, the calculator increases the earth cable size until both the fault current rating and loop impedance requirements are met.
- Step 3: If no suitable earth size is found, the active size is used. If you need a larger earth cable, select it manually.
If the earth core size is selected manually, the selected earth size is still checked against [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000). The fault rating and earth loop impedance are also checked when these options are selected.
[Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) does not specify aluminium earth sizes. They are calculated based on the impedance and fault rating of the equivalent copper earth cables. Click [here](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) for more details.
### Parallel single-core cables
By default, the earth fault rating is checked per earth cable, i.e. no earth fault current split is considered.
However, in high current installations, the option [Combined fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#allowEarthFaultCurrentSplitInfo) can be enabled, and earth fault rating will be based on an equal split of fault current across parallel earth cables. See [Combined fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#allowEarthFaultCurrentSplitInfo) for more information.
The loop impedance is checked on the combination of parallel active and earth cables, i.e. an equal earth fault current split is considered.
For parallel active and parallel earth cables, the combined active size is calculated as:
\\(S\_{active\\\_combined} = \\dfrac {S\_{active} \\cdot m}{n} \\)
Where,
- **Sactive** is the size of one of the active cables in mm2.
- **m** is the number of parallel phase cables.
- **n** is the number of parallel earth cables.
The combined active size is then used to select the minimum earth size from [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000).
For multiple earth cables, the calculator checks that each earth cable is equal to or larger than the minimum earth cable required for one individual active conductor.
For example, in [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) the minimum earth cable size for a 240 mm2 active cable is 95 mm2. If two earth cables are selected, the minimum individual earth cable size is still 95 mm2.
If the combined active size is larger than 630 mm2, the earth size is calculated according to [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) as follows:
- Copper: Minimum 25% of the combined active size.
- Aluminium: Minimum 40% of the combined active size.
For high current installations, the option [Ignore table 5.1](https://www.jcalc.net/cable-sizing-calculator-as3008#ignoreTable51Info) can be enabled, and [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) will be enforced up to 120 mm2 (copper) or 240 mm2 (aluminium) only. See [Ignore table 5.1](https://www.jcalc.net/cable-sizing-calculator-as3008#ignoreTable51Info) for more information.
- **Number of earth cores or cables:**
| | |
|---|---|
| Multi-core cables | Matches the number of parallel cables. Cannot be changed. |
| One single-core [cable group](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) | One or two earth cables. |
| Multiple single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) | Any number of earth cables between one and the number of parallel cable groups. |
- **Advanced options:** Select to show the following two options.
- **Ignore table 5.1 sizes:** Ignores earth sizes specified in [Table 5.1](https://www.jcalc.net/minimum-cable-earth-sizes-as3000) in AS/NZS 3000. Earth size will be based on earth fault current and loop impedance only.
This allows for more economical earth cable sizes.
This option is only available for:
- Three-phase, single-core cables, excluding mains.
- Number of parallel cable groups \> 1.
- [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled.
- The calculated earth size is ≥ 120 mm2 (copper) or ≥ 240 mm2 (aluminium).
- **Combined earth fault rating:** The fault rating of the earth cables is based on an equal split of earth fault current across the parallel earth cables.
This allows for more economical earth cable sizes.
This option is only available for:
- Three-phase, single-core cables, excluding mains.
- Number of parallel cable groups \> 1.
- Number of parallel earth cables \> 1.
- [Check fault rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) and [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) are enabled.
- The calculated earth size is ≥ 120 mm2 (copper) or ≥ 240 mm2 (aluminium).
**Important:** To ensure safety, it is essential that the parallel earth cables:
- are the same length,
- follow the same route,
- are mechanically protected,
- insulated,
- and separated from the live cables to prevent direct faults between phase and earth cables.
## Installation parameters
- **Formation:** Trefoil or laid flat.
- **Installation method:** Select the installation method. Consider the worst-case section of the cable installation. Which is the installation section with the lowest current rating.
## Installation derating parameters
- **Show derating options:** Check this box if you want to specify derating options. If not, the following default derating options are used.
| | Australian conditions | New Zealand conditions |
|---|---|---|
| Number of cables or cable groups | 1 | 1 |
| Air temperature | 40 °C | 30 °C |
| Soil temperature | 25 °C | 15 °C |
| Cable depth | 0\.5 m | 0\.5 m |
| Soil resistivity | 1\.2 °C.m/W | 1\.2 °C.m/W |
| Circuit derating | None | None |
- **Cable support:** The cable support options depend on the installation method.
- **Number of cables (or cable groups):** The number of multi-core cables or single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) in this installation. This includes parallel cables in this circuit and cables from any other circuits included in the same installation.
The standard refers to this parameter as the Number of Circuits. And the standard treats parallel cables as multiple circuits. jCalc uses the names "Number of cables" and "Number of cable groups" instead of "Number of Circuits" to make it more intuitive, especially when parallel cables are used.
Note that the parameter [number of parallel cables (or cable groups)](https://www.jcalc.net/cable-sizing-calculator-as3008#numberOfCablesInfo) under Cable Type specifies the number of parallel cables in this circuit only. This parameter considers the parallel cables in this circuit, and cables from any other circuits in the same installation.
All cables in the installation must be considered, because heat from adjacent cables affects the current rating and voltage drop.
For multi-core cables, each cable is considered in the derating. For single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition), each cable group is considered in the derating -not the individual cables for each phase, the neutral or the earth.
Multiple cables (or cable-groups) are not supported for "Exposed to Sun" installations by AS/NZS 3008.
Examples:
Multi-core (number of cables = 3)
Single-core (number of [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) = 3)
- **Space between cables, cable groups or enclosures:** Select the spacing between multi-core cables, single-core [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition) or enclosures (underground multi- and single-core). The table below shows the spacing that can be selected for different installations and cable types.
| In air, multi-core cables | |
|---|---|
| Space between the edges of cables. | |
| Touching |  |
| Spaced 1D | The diameter of the largest cable.  |
| In air, single-core cables | |
| Space between the edges of [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition). | |
| Touching |  |
| Spaced 1D | The diameter of the largest cable.  |
| Underground, multi-core cables | |
| Space between the centres of cables. | |
| Touching | Buried direct  Underground enclosure  |
| 150 mm | |
| 300 mm | |
| 450 mm | |
| 600 m | |
| Underground, single-core cables | |
| Space between the centres of [cable groups](https://www.jcalc.net/cable-sizing-calculator-as3008#cableGroupDefinition). | |
| Touching | Buried direct  Underground enclosure  |
| 150 mm | |
| 300 mm | |
| 450 mm | |
| 600 m | |
- **Number of tiers:** Number of tiers.
- **No of horizontally tiered racks:** The number of horizontal tiers (rows) of racks or ladders installed above each other. The minimum vertical space between racks is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
- **No of horizontally tiered unperforated trays:** The number of horizontal tiers (rows) of trays installed above each other. The minimum vertical space between trays is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
- **No of horizontally tiered perforated trays:** The number of horizontal tiers (rows) of trays installed above each other. The minimum vertical space between trays is 300mm. See AS/NZS 3008:2017 Tables 23 and 24.
- **No of vertical back-to-back perforated trays:** On or two vertical back-to-back trays. The minimum vertical space between trays is 230mm. ee AS/NZS 3008:2017 Tables 23 and 24.
- **Air temperature (°C):** For cables installed in air. The defaults (no derating) are.
- Australian conditions: 40°C
- New Zealand conditions: 30°C
- **Soil temperature (°C):** For cables installed underground. The defaults (no derating) are:
- Australian conditions: 25°C
- New Zealand conditions: 15°C
- **Cable depth (m):** The default (no derating) is 0.5 m.
- **Soil resistivity (°C.m/W):** The default (no derating) is 1.2 °C.m/W.
## Conduit parameters
- **Calculate conduit:** Check this box if you want to calculate conduit sizing. The option will only show for installations with enclosures. Conduit sizing is based on Tables C10, C11 and C12 in AS/NZS 3000:2018. Click [here](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation) for more details.
- **Conduit type:** Select the conduit type. Click [here](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation) for more details.
- **Conduit size (mm):** Select a conduit size or select Auto. Click [here](https://www.jcalc.net/cable-sizing-calculator-as3008#conduitCalculation) for more details.
## Short circuit protection parameters
- **Check short circuit rating:** Select to check the fault rating of the cable.
- **Check loop impedance:** Select to check the earth loop impedance of the circuit. In other words, check if the specified protection device will trip for an earth fault when the specified cable is used.
The external source impedance is estimated, calculated, or specified (measured). The method depends on the selected [protection device](https://www.jcalc.net/cable-sizing-calculator-as3008#protectionInfo). When it is calculated, it is calculated from the prospective earth fault current.
| Protection device | Loop impedance method |
|---|---|
| [MCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCB) | Estimated, Calculated or Measured |
| [MCCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCCB) | Calculated |
| [Generic device](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoGeneric) | Calculated |
- **Protection:** Select the protection device. MCB, MCCB, or Generic.
| Protection device | Description |
|---|---|
| [MCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCB) | Miniature circuit breakers. From 1 A to 125 A. |
| [MCCB](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoMCCB) | Moulded case circuit breakers. From 16 A to 3200 A. |
| [Generic device](https://www.jcalc.net/cable-sizing-calculator-as3008#shortCircuitHeadingInfoGeneric) | Generic phase and earth current fault protection. With definite time settings. |
## Short circuit protection parameters -MCB
- **MCB curve type:** The MCB tripping curve: B, C or D.
MCBs are manufactured according to AS/NZS 60898.1, which specifies trip current ranges for the MCB curve types.
Calculations in AS/NZS 3000 and jCalc is based on the mean values of the ranges.
| Curve type | Trip current AS/NZS 60898.1 | Trip current AS/NZS 3000 and jCalc |
|---|---|---|
| B | 3-5 x rated current | 4 x rated current |
| C | 5-10 x rated current | 7\.5 x rated current |
| D | 10-20 x rated current | 12\.5 x rated current |
- **MCB rating:** Select an MCB rating or select Auto. The auto option will automatically select the recommended size from Tables C6 and C7 in AS/NZS 3000-2018. In Auto, the MCB size is selected for the load current. And then checked against the cable.
- **Source impedance:** Specify the method to determine the source (external) loop impedance.
- **Estimate:** Estimate according to AS/NZS 3000-2018, i.e. assume that 80% voltage is available at the cable source during an earth fault.
- **Calculate:** Calculate from the prospective fault current.
- **Measured:** Specify the measured impedance in Ohm.
- **Prospective earth fault current (kA):** Specify the prospective earth fault current on the primary side of the circuit breaker. This parameter is required when the [source impedance method](https://www.jcalc.net/cable-sizing-calculator-as3008#sourceImpedanceTypeInfo) is selected as "Calculate". It is used to calculate the external source loop impedance for earth faults.
## Short circuit protection parameters -MCCB
- **Make:** Select between Schneider and Terasaki TemBreak Pro.
- **Model:** Select the model. Note that the number in the model name represents the current rating of the circuit breaker. For example, a Schneider NXS100 is rated for 100A, and a Terasaki P250 for 250A.
- **CB fault rating:** The fault current rating of the circuit breaker. This affects the let-though energy.
- **Trip unit:** Select between Thermal Magnetic, Micrologic 2.3 (NSX) or Micrologic 2.0. (NS)
- **Thermal-magnetic**
- **Trip unit rating:** Select the current rating or select Auto. The following are automatically selected in Auto: trip unit rating, thermal trip setting, and magnetic trip setting. The trip unit rating, and the thermal trip setting, are selected to be ≥ the load current.
- **Thermal trip:** The thermal trip setting can be selected if the trip unit rating is selected manually.
- **Magnetic trip:** The magnetic trip setting can be selected if the trip unit rating is selected manually.
- **Micrologic 2.3 (NSX) and Micrologic 2.0 (NS)**
- **Trip unit rating:** Select the current rating or select Auto. The following are automatically selected in Auto: trip unit rating, thermal trip setting, short-time trip setting, and instantaneous trip setting. The trip unit rating, and the thermal trip setting, are selected to be ≥ the load current. The short-time trip setting is selected as 6x the thermal trip setting.
- **Thermal trip:** The thermal trip setting can be selected if the trip unit rating is selected manually.
- **Short-time trip:** The short-time trip setting can be selected if the trip unit rating is selected manually.
- **Instantaneous trip:** The instantaneous trip setting can be selected if the trip unit rating is selected manually. Note that there is no instantaneous trip on the Micrologic 2.0 (NS) trip units in the calculator. It is modelled as a short-time trip instead. The catalogue refers to the trip as instantaneous. However, it behaves like a short-time trip when compared to other electronic trip units.
- **Prospective phase fault:** The prospective phase fault current on the primary side of the circuit breaker. Specify the 3-phase fault current for "3 Phase AC" supplies. Or specify the phase-to-neutral fault current for "1 Phase AC" and "DC" supplies. When [Check short circuit rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) is selected, this parameter is used to calculate the phase fault let-through-energy (I2t) of the circuit breaker and compares it against the fault energy rating of the cable.
- **Prospective earth fault (kA):** The prospective earth fault current on the primary side of the circuit breaker. Specify the phase-to-earth fault current for "3 Phase AC", "1 Phase AC" and "DC" supplies. When [Check loop impedance](https://www.jcalc.net/cable-sizing-calculator-as3008#checkLoopImpedanceInfo) is selected, this parameter is also used to calculate the external source loop impedance for earth faults. When [Check short circuit rating](https://www.jcalc.net/cable-sizing-calculator-as3008#checkFaultRatingInfo) is selected, it is also used to calculate the earth fault let-through-energy (I2t) of the circuit breaker and compares it against the fault energy rating of the cable.
## Short circuit protection parameters -Generic
- **Current limiting (yes/no):** Specify if the circuit breaker or fuse can limit the fault energy. For example current limiting fuses and MCCBs.
- **Prospective phase fault current (kA):** The prospective fault current on the primary side of the circuit breaker. It is used to calculate the phase fault current at the load. It is used to check the phase fault current rating of the live and neutral cores of the cable if the current limiting option is not selected.
- **Phase fault let-through energy (A2s):** It is checked against the fault energy rating of the live and neutral cores of the cable if the current limiting option is not selected The let-through energy (I2t) is available on current-limiting curves from the device manufacturer. It is a function of the prospective phase fault current.
- **Phase fault trip time (ms):** The phase fault clearing time of the protection device. It is used to check the fault current rating of the live and neutral cores of the cable if the current limiting option is not selected.
- **Prospective earth fault current (kA):** The prospective phase-to-earth fault current. It is used to calculate the earth fault current at the load. It is used to calculate the external earth loop impedance. It is used to check the earth fault current rating of the live and earth cores of the cable if the current limiting option is not selected.
- **Earth fault let-through energy (A2s):** It is checked against the fault energy rating of the live and earth cores of the cable if the current limiting option is not selected. The let-through energy (I2t) is available on current-limiting curves from the device manufacturer. It is a function of the prospective earth fault current.
- **Earth fault trip current (A):** The earth fault trip setting of the protection device. It is used to check the earth loop impedance of the circuit.
- **Earth fault trip time (ms):** The earth fault clearing time of the protection device. It is used to check the earth fault current rating of the live and earth cores of the cable if the current limiting option is not selected.
## Cable group definition
A **cable group** refers to a set of single-core cables in a circuit. For example, red, white, and blue phase single-core cables.
For three-phase applications, A **cable group** includes Three-phase cables, the neutral cable (if applicable), and the earth cable. It can be installed in a flat or trefoil formation.
For single-phase applications, A **cable group** includes a phase cable, a neutral cable, and an earth cable.
Each set is counted as one separate cable group.
- Do not count the three phases.
- Do not count the neutral.
- Do not count the earth cable.
Example: Two parallel single-core cable groups.
Example: Two parallel multi-core cables.
## Cable current rating calculation
The current ratings are selected from Tables 4 to 21 in AS/NZS 3008-2017. It is based on cable type, insulation type and the cable installation method.
For Australian conditions, Tables 4 to 21 are based on an ambient temperature of 40°C and a ground temperature of 25°C.
For New Zealand conditions, Tables 4 to 21 are based on an ambient temperature of 30°C and a ground temperature of 15°C.
The cable sizing calculator supports the following conductors:
- Copper (solid, stranded and flexible).
- Aluminium (solid, stranded and flexible).
## Cable current derating calculation
The current derating for the cables has been implemented according to AS/NZS 3008:2017.
## Cable impedance calculation
The impedance is calculated as:
\\(Z\_c = \\sqrt{R\_c^2 + X\_c^2}\\)
Where,
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
- **Xc** is the cable [reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance) in Ω/km.
## Loop impedance calculation
There are three methods to calculate the maximum loop distance, depending on how the source impedance is determined.
| Source impedance | Calculation |
|---|---|
| Estimated according to AS/NZS 3000. (MCB protection only) | Max. distance. \\(L\_{max}=\\dfrac{0.8 \\cdot V\_{1\\phi} \\cdot 1000}{I\_{min} \\cdot (Z\_{p} + Z\_{e}) }\\) |
| Calculated from prospective earth fault current. (All protection types). | Max. total loop impedance. \\(Z\_{max}= \\dfrac{V\_{1\\phi}} {I\_{min}} \\) Source impedance. \\(Z\_{s}= \\dfrac{ V\_{1\\phi} } { I\_{f} \\cdot 1000 } \\) Max. distance. \\( L\_{max} = \\dfrac {\\left( Z\_{max} - Z\_{s} \\right) \\cdot 1000 } { Z\_{p} + Z\_{e} } \\) |
| Measured. (MCB protection only) | Max. total loop impedance. \\(Z\_{max}= \\dfrac{V\_{1\\phi}} {I\_{min}} \\) Max. distance. \\( L\_{max} = \\dfrac {\\left( Z\_{max} - Z\_{s} \\right) \\cdot 1000 } { Z\_{p} + Z\_{e} } \\) |
Where:
- **V1Φ**, single-phase-to-earth or DC-to-earth voltage.
- **Imin**, minimum trip current of protection device.
- **If**, prospective earth fault current.
- **Zs**, measured source impedance in Ω.
- **Zmax**, maximum allowable total loop impedance in Ω.
- **Zp**, phase core impedance in Ω/km.
- **Ze**, earth core impedance in Ω/km.
- **Lmax**, maximum allowable cable distance in meters.
For parallel cables, the phase core impedance (**Zp**) is divided by the number of phase cores (**m**), and the earth core impedance (**Ze**) is divided by the number of earth cores (**n**).
## Voltage drop calculation with worst-case load power factor
This is the default method in the calculator.
It is the simplest. The most conservative. And the most often used.
The worst-case power factor is when the cable and load power factors are the same.
The voltage drop formulas are shown below.
| | |
|---|---|
| 1 Phase AC | \\(\\Delta V\_{1\\phi}=\\dfrac{I \\cdot L \\cdot 2 \\cdot Z\_{c}}{1000}\\) |
| 3 Phase AC | \\(\\Delta V\_{3\\phi}=\\dfrac{I \\cdot L \\cdot \\sqrt{3} \\cdot Z\_{c}}{1000}\\) |
| DC | \\(\\Delta V\_{dc}=\\dfrac{I \\cdot L \\cdot 2 \\cdot R\_{c\\\_ph}}{1000}\\) |
Where,
- **I** is the load current in ampere (A).
- **L** is the cable distance in meters (m).
- **Zc** is the cable impedance in Ω/km.
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
The impedance **Zc** for the worst-case power factor is calculated as:
\\(Z\_c = \\sqrt{R\_c^2 + X\_c^2}\\)
Where,
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
- **Xc** is the cable [reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance) in Ω/km.
## Voltage drop calculation with specified load power factor
The specified load power factor is used to calculate the voltage drop.
This will result in a lower voltage drop.
It is useful when the power factor of the load is known. And it is stable at full load. For example, electrical motors.
The formulas are shown below.
| | |
|---|---|
| 1 Phase AC | \\(\\Delta V\_{1\\phi} {=} \\dfrac{I {\\cdot} L {\\cdot} 2 {\\cdot} \[R\_{c} {\\cdot} \\cos (\\theta) {+} X\_{c} {\\cdot} \\sin (\\theta)\]}{1000}\\) |
| 3 Phase AC | \\(\\Delta V\_{3\\phi} {=} \\dfrac{I {\\cdot} L {\\cdot} \\sqrt{3} {\\cdot} \[R\_{c} {\\cdot} \\cos (\\theta) {+} X\_{c} {\\cdot} \\sin (\\theta)\]}{1000}\\) |
| DC | \\(\\Delta V\_{dc}=\\dfrac{I \\cdot L \\cdot 2 \\cdot R\_{c\\\_ph}}{1000}\\) |
Where,
- **I** is the load current in ampere (A).
- **L** is the cable distance in meters (m).
- **Rc** is the cable [resistance](https://www.jcalc.net/cable-sizing-calculator-as3008#resistance) in Ω/km.
- **Xc** is the cable [reactance](https://www.jcalc.net/cable-sizing-calculator-as3008#reactance) in Ω/km.
- **θ = arccos(pf)**, and **pf** is the specified load power factor.
## Cable resistance
The calculator selects the resistance, Rc, values from Table 34, Table 35 and Table 37 in AS/NZS 3008.
The selection is based on the "Conductor Temperature" selection under the voltage drop options.
| Conductor temperature | Resitance selection |
|---|---|
| Calculated | The cable resistance is lower at lower conductor temperatures. The conductor temperature is calculated. The resistance is selected from the column in the relevant resistance table with the next higher temperature. This is described in section 4.4. in AS/NZS 3008. |
| Maximum | The maximum allowable insulation temperature is used. The resistance is selected from the column in the relevant resistance table with the maximum allowable insulation temperature. This is the most conservative option. |
Table 36 (shaped conductors) is not used. Table 35 (circular conductors) is used instead. It is more conservative.
AS/NZS 3008 does not specify the DC resistance. The specified AC values are used.
## Cable reactance
The calculator selects the reactance values, Xc, from Table 30 and Table 31 in AS/NZS 3008.
## Short circuit calculation
The short circuit capacity of the cables is calculated according to AS/NZS 3008-2017 as
\\(I^2t = K^2S^2\\)
Where:
- **I** is the short circuit current capacity in amperes,
- **t** is the short circuit duration in seconds.
- **S** is the cross-sectional area of the conductor.
- **K** is a constant that is selected from Table 52 in AS/NZS 3008-2017.
The fault constant, **K**, is based on the insulation material, the initial conductor temperature, and the final conductor temperature.
The calculator uses the maximum allowable operating temperature as the initial conductor temperature. For example, 75°C is used for PVC insulated cables, 90°C is used for XLPE insulated cables, and 110°C is for XLPE 110°C.
The maximum allowable short circuit temperature from Table 53 in AS/NZS 3008-2017 is used as the final conductor temperature i.e. 160°C for PVC and 250°C for XLPE.
The calculator selects the K value from Table 52 in AS/NZS 3008, based on the initial conductor temperature and the maximum allowable short circuit temperature.
## Conduit calculation
Conduit size calculations are based on Tables C10, C11 and C12 in AS/NZS 3000:2018
The tables specify the maximum number of cables for a specific cable size, cable type, consuit type and conduit size.
The tables cover only PVC and XLPE insulation. Not elastomer (rubber) insulation.
| Table | Cable type | Sizes |
|---|---|---|
| C10**a** | Single-core cables | 1 to 630 mm2 |
| C11 (circular) | Two-core and earth cables | 1\.5 to 25 mm2 |
| C11 (flat)**b** | Two-core and earth cables | 1 to 16 mm2 |
| C12**c** | Four-core and earth cables | 1\.5 to 120 mm2 |
- **Note a:** The cable size for single-core cables is based on the largest cable in a cable group. For example, a 3x1C+E single-core group (16 mm2 actives, 6 mm2 earth), is calculated as a 4 x 16 mm2 cables.
- **Note b:** Flat multi-core cables are not currently supported in jCalc.
- **Note c:** PVC and XLPE insulated cables are specified separately in Table C12. They have minor differences. jCalc uses the more conservative PVC data for both XLPE and PVC cables.
Tables C10, C11 and C12 covers four conduit types.
| Conduit type | Size range |
|---|---|
| Heavy duty rigid conduit | 20 to 150 mm |
| Corflow | 100 to 150 mm |
| Medium duty corrugated | 20 to 40 mm |
| Medium duty rigid | 16 to 50 mm |
Here is an example of how the maximum number of cables is specified in Table C12.
| Cable size mm2 | Medium duty corrugated | | | |
|---|---|---|---|---|
| 20mm | 25mm | 32mm | 40mm | |
| 1\.5 | 0 | 1 | 1 | 2 |
| 2\.5 | 0 | 0 | 1 | 1 |
| 4 | 0 | 0 | 1 | 1 |
| 6 | 0 | 0 | 1 | 1 | |
| Shard | 184 (laksa) |
| Root Hash | 11101342250389246584 |
| Unparsed URL | net,jcalc!www,/cable-sizing-calculator-as3008 s443 |