This calculator uses the accurate voltage drop method described by the Standard AS/NZS 3008.1.

**Accurate voltage drop calculations will result in smaller cable sizes. **

Note that cable operating temperature is not considered with this calculator – use Cable Pro Web software for the highest accuracy and the smaller cable sizes.

The Wiring Rules AS/NZS 3000:2018 sets the limits for voltage drop within an installation.

Please enter the parameters below and press Calculate.

## Calculation method and equations

We use an accurate method for voltage drop which considers power factor. Note this calculator does not consider cable operating temperature (which affects resistance) and is the most accurate.

For single phase AC the voltage drop is calculated as:

\(\Delta V_{1\phi-ac}=I L\{2(R_c cos \theta + X_c sin \theta)\}\)

For three phase AC (balanced) the voltage drop is calculated as:

\(\Delta V_{3\phi-ac}=I L\{\sqrt{3}(R_c cos \theta + X_c sin \theta)\}\)

Where I is the load current and L is the length of the cable.

The current ratings, cable resistance and cable reactance values used by this calculator were taken from AS/NZS 3008.1.1:2017 (based on IEC Standards).

**The effect of power factor on voltage drop explained:** For small cable sizes which have greater resistance than reactance a higher power factor results in a larger voltage drop. However for large cable sizes which have a high reactance compared with resistance the opposite is true.

## Load units conversion equations

The load conversion **from kW to A** for single phase is calculated as:

\(I_{(A)}=\frac{1000\times P_{(kW)}}{PF\times V_{(V)}}\)

For three phase is calculated as:

\(I_{(A)}=\frac{1000\times P_{(kW)}}{\sqrt{3}\times PF\times V_{P-P(V)}}\)

Where PF is power factor and \(V_{P-P}\) is phase-to-phase voltage (i.e. 3-phase voltage).

The load conversion **from kVA to A** for single phase is calculated as:

\(I_{(A)}=\frac{1000\times S_{(kVA)}}{V_{(V)}}\)

For three phase is calculated as:

\(I_{(A)}=\frac{1000\times S_{(kVA)}}{\sqrt{3}\times V_{P-P(V)}}\)

The load conversion **from horsepower (hp) to A** for single phase is calculated as:

\(I_{(A)}=\frac{746\times hp}{V_{(V)}\times PF}\)

For three phase is calculated as:

\(I_{(A)}=\frac{746\times hp}{\sqrt{3}\times V_{P-P(V)}\times PF}\)

## Related Resources:

### Cable Size Calculator

This calculator determines minimum cable size using the method described by the Standard AS/NZS 3008.1.1 and uses the accurate voltage drop method.

### Earth Cable Size Calculator

Earth cable size can be determined using Table 5.1 in AS/NZS 3000 or by calculation.