Voltage drop in a circuit represents the vector difference between the supply end and the load end. Accurate voltage drop calculations result in smaller cable sizes.
Use ELEK Cable Pro Web Software for your electrical calculations (includes live technical support).
How to calculate voltage drop
The balanced three-phase voltage drop equation is below. For single phase voltage drop replace the \(\sqrt{3}\) with 2 and \(V_{3ph}\) with \(V_{1ph}\).
Refer to our tutorial with a worked example of how to calculate voltage drop.
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.
Allowable voltage drop limits
Refer to the article Voltage Drop Limits for LV Installations which lists all the voltage drop and voltage rise limits from the Standard AS/NZS 3000:2018.
How to convert power or horsepower into current
The equations to convert the units of the electrical load inputs used by the calculator are as follows.
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:
\(I_{(A)}=\frac{746\times hp}{\sqrt{3}\times V_{P-P(V)}\times PF}\)
