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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.

Underground wiring enclosure

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See Also

Load parameters

Cable parameters

Installation parameters

Short circuit protection parameters

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.

Tables 4 to 21 are based on an ambient temperature of 40°C and a ground temperature of 25°C.

The cable sizing calculator supports the following conductors:

Flexible cables are not supported yet.

Cable current derating calculation

The current dearing for the cables has been implemented according to AS/NZS 3008:2017.

Cable impedance calculation

The impedance is calculated as:

\(Z_c = \sqrt{R_c^2 + X_c^2}\)

This method calculates the impedance for the worse case power factor, i.e. when the cable and load power factor is the same.

The cable sizing calculator uses the resistance Rc from Table 35 in AS/NZS 3008-2017 .

The reactance for single core cables is selected from the flat, touching column in from Table 30 in AS/NZS 3008. This is the worse case scenario.

The reactance for multi-core core cables is selected from the circular conductors column in from Table 30 in AS/NZS 3008. This is the worse case scenario.

Loop impedance calculation

The maximum loop distance is calculated as:

\(L_{max}=\dfrac{0.8 \cdot V_{1\phi} \cdot 1000}{I_{min} \cdot Z_{c} }\)


Voltage drop calculation

The three phase AC voltage drop is calculated as:

\(V_{d3\phi}=\dfrac{I L (\sqrt{3}Z_c)}{1000}\).

The single phase AC voltage drop is calculated as:

\(V_{d1\phi}=\dfrac{I L (2 Z_c)}{1000}\)

Where I is the load current, L is the distance, and Zc is the cable impedance in Ohm/km.

Short circuit calculation

The short circuit capacity of the cables is calculated according to AS/NZS 3008-2017 as:

\(I^2t = K^2S^2\)


K It is based on the insulation material, initial conductor temperature and final conductor temperature.

The calculator assumes that the initial conductor temperature is the maximum allowable operating temperature for the insulation type, i.e. 75°C for PVC, and 90°C for XLPE 90°C, and 110°C 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 following K values are used.

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