Cable short circuit fault current calculator AS/NZS 3008

The calculator calculates the short circuit fault current at a specified distance in a cable run, based on the source short circuit fault current level.

Voltage (V)

Source fault current (kA)

Cable size (mm2)

Distance (m, ft)

Parameters

• Voltage (V): Specify the voltage and select the phase arrangement: 1 Phase AC or 3 phase AC. Currently supports AC only.
• Source fault current (kA): Specify the prospective fault current of the switchboard that the load is supplied from.
• Standard cable size: Select a standard cable size in mm2 as defined in AS/NZ 3008.
• Distance (m, ft):  Specify the estimated cable length in meters of feet.

How to calculate the Cable short circuit fault current?

• Cable short circuit fault current calculator calculates the single and three phase load fault current as follows:
• $$I_{1\phi-load-fault}=\dfrac{V_{source}} {(Z_{source}+2\cdot Z_{cable})}$$
• $$I_{3\phi-load-fault}=\dfrac{V_{source}} {(Z_{source}+\sqrt{3}\cdot Z_{cable})}$$
• The source impedance is calculated as:
• $$Z_{source}=\dfrac{V_{source}} {I_{sourcefault}}$$
• The cable impedance is calculated as:
• $$Z_{cable} = \sqrt{R_{cable}^2 + X_{cable}^2}$$. 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 short circuit fault current calculator uses the resistance $$R_{cable}$$ from Table 35 in AS/NZS 3008 at 75°C , and the reactance values $$X_{cable}$$ from Table 30 in AS/NZS 3008 for multi-core PVC circular conductors.