Voltage Drop Calculator

Estimate cable resistance and voltage drop using current, route length, conductor size and supply voltage.

This simplified resistivity calculation does not replace full BS 7671 design checks or manufacturer cable data.

How voltage drop is calculated

Longer routes, higher current and smaller conductors increase voltage drop. For two-wire circuits, both outgoing and return conductors normally contribute to resistance.

For design context, read the wiki guidance on BS 7671 for fire and emergency systems, cabling and wiring rules and UK cable selection.