Cable Sizing Calculator

Note:

The above cable sizing calculator is based on the values given in AS/NZS 3008.1.1-2017. Please read the parameters below for more information. Incorrect data input will return incorrect results, only use this calculator as a guide, please check your results against AS/NZS3008.1.1-2017. This calculator is to be used at your own discretion, with responsibility for results provided being wholly with the user. CMI Electrical shall not be held responsible for any errors or omissions that may occur from using the results of this calculator and will not be held liable for any damages. Any errors are to be reported to CMI Electrical immediately.

Current rating:

The current rating is selected from Tables 4 to 21 in AS/NZS 3008.1.1-2017.
The cable ratings in are based on an ambient temperature of 40°C and a ground temperature of 25°C.
The current rating is based on the cable type, the insulation type and the cable installation method.
The cable sizing calculator considers solid or stranded & flexible for copper conductors only. Aluminum is solid only.

Derating:

No derating is currently applied to the current rating from Tables 4 to 21 in AS/NZS 3008.1.1-2017
It is assumed that the maximum ambient temperature is 40°C and the maximum ground temperature is 25°C. For higher temperatures, a derating will have to be applied according to AS/NZ 3008.1.1-2017 Table 27.
It is also assumed that the cable is installed as specified in Figure 2 and Table 3 in AS/NZS 3008.1.1-2017 to avoid derating, and there there is only one circuit. For groups of circuits, the cable will have to be derated according to tables 22 to 26.
How to use the derated factors in the calculator: Divide the load by the derating factor from tables 22 to 27, and enter the new load value in the calculator.

Voltage drop calculation:

The single phase AC voltage drop is calculated as:
Vd1ϕ=IL(2Zc)1000, where I is the load current, L is the distance, and Zc is the cable impedance in Ω/km.
The three phase AC voltage drop is calculated as:
Vd3ϕ=IL(3–√Zc)1000.

The impedance is calculated as:

Zc=SQRT(R2c+X2c). This method calculates the impedance for the worst-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 3008.1.1-2017 at 75°C.
The reactance for single core cables is selected from the flat, touching column from Table 30 in AS/NZS 3008.1.1-2017. This is the worst-case scenario.
The reactance for multi-core cables is selected from the circular conductors column in Table 30 in AS/NZS 3008.1.1-2017. This is the worst-case scenario.
Short circuit calculation
The short circuit capacity of the cables is calculated according to AS/NZS 3008.1.1-2017 as: I2t=K2S2, where, I is the short circuit current 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 3008.1.1-2017. It is based on the insulation material, initial conductor temperature and final conductor temperature. A value of 111 is used for PVC cables and 143 for XLPE cables. 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. The maximum allowable short circuit temperature from Table 53 in AS/NZS 3008.1.1-2017 is used as the final conductor temperature i.e. 160°C for PVC and 250°C for XLPE.