Voltage drop

Enter one-way cable length

Measure the route from the source to the load. The DC and single-phase calculations account for the outgoing and return paths; do not double the length yourself. Use conductor cross-section, not the outside diameter of an insulated cable.

A drop limit is not an ampacity check

Conductor temperature affects resistance, while AC power factor and reactance affect the drop estimate. A conductor that meets the entered percentage may still be unsuitable for its current or installation. Check ampacity, protection, and installation requirements separately.

Interpreting percentage drop

Percentage drop compares the calculated voltage loss with the entered supply voltage. A one-volt loss is a much larger fraction of a 12 V circuit than of a 230 V circuit. Enter current at the operating condition you want to assess, especially when a load has different running and starting currents. The maximum-distance mode answers the same relationship in reverse for the drop limit you choose.

Resistance increases with route length and decreases with conductor cross-sectional area in the model. Doubling area therefore reduces the resistive part of the drop by half when the other conditions are unchanged. AC calculations also depend on the selected circuit arrangement, reactance, and power factor, so this simple comparison does not describe every AC case. Check voltage at the equipment terminals against its requirements rather than treating any customary percentage as universally acceptable. Connection resistance and extra cable sections must be considered separately if they are not represented by the entered cable data.

Formula

ΔV = path factor × I × L × (R cosφ + X sinφ) / parallels. DC uses 2ILR.