Electrical
Electrical Wire Size Calculator
Wire gauge for a given load, with the continuous-load uplift and voltage drop both taken into account.
Result
A planning estimate, not a code calculation. Conductor sizing, overcurrent protection and load calculations are governed by the NEC as adopted and amended where you are, and by the listing of the equipment involved. Have the design confirmed by a licensed electrician and inspected. Ampacities here are the 75 degree copper and aluminium columns, before any derating for ambient temperature or for more than three current-carrying conductors in a raceway.
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About this calculator
Why does a long run need thicker wire?
Resistance rises with length, so voltage falls along the run. Code treats 3% on a branch circuit as the practical limit, and on a long run that requirement bites well before ampacity does.
What is a continuous load?
One expected to run for three hours or more, such as lighting or an EV charger. Code requires the conductor and breaker to be sized at 125% of it.
Is aluminium acceptable?
For larger feeders it is common and permitted where the terminations are listed for it. It needs a larger size for the same current and correct anti-oxidant treatment at terminations.
The formula
design amps = load x 1.25 if continuous; voltage drop = 2 x K x amps x distance / circular mils
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