Wire-size calculator
Smallest conductor that satisfies both ampacity and voltage drop for the run.
220.87 uses the utility's measured maximum demand and often shows an existing service is adequate. 220.83 sums connected load.
Blank means no adequacy check is made — it is not treated as a failure.
Required. 220.87 cannot be used where any of these are present, so this is not assumed either way.
One more answer needed
Before this calculation can run: does the service have a solar or wind system, or any form of peak load shaving? NEC 220.87 cannot be used where it does, so the question has to be answered rather than assumed.
The calculation is free. The document is not.
This page gives you the number. The permit packet — the load-calculation worksheet in the form a plan reviewer reads, the branch circuit, and the code section cited next to every figure — is the paid artifact. See a sample or see plans.
Design aid only — a code-cited calculation, not a stamped plan set, and no PE seal. Acceptance is never guaranteed: authorities having jurisdiction amend and interpret the code. Verify with a licensed professional before installation. Only the 220.83 and 220.87 methods are offered here; the 220.82 optional method is not implemented.
- Limited by
- voltage_drop
- Ampacity
- 50 A
- Voltage drop
- 2.59%
- Req. ampacity
- 25 A
NEC 310.16 derated + 210.19(A) voltage drop + 210.19(A) 125% continuous
Assumes 2 current-carrying conductors (duplex/paired cable), 30 °C ambient, 90 °C insulation as the derating basis, capped at the 75 °C termination column per 110.14(C).
Design aid only — not a P.Eng stamp. Verify with a licensed professional before installation. ABYC marine values are pending licensed verification.