NEC Motors
NEC motor circuits use a specific 125% conductor sizing rule distinct from the general continuous-load provisions.
The NEC's motor circuit conductor sizing rule (commonly summarized as the "125% rule," rooted in Article 430) is specific to motors — distinct from, though numerically similar to, the general continuous-load safety factor covered elsewhere in the code.
Motor branch circuit conductors are typically sized at 125% of the motor's full-load current rating (from the motor's nameplate or the applicable NEC full-load current table) — a provision specific to Article 430 rather than the general continuous-load logic applied to other equipment.
| Element | What it's based on |
|---|---|
| Branch circuit conductor | 125% of full-load current |
| Branch circuit short-circuit and ground-fault protection | A separate percentage of full-load current, coordinated to tolerate starting current without nuisance tripping |
| Overload protection | Sized to the motor's actual full-load current and service factor, protecting against sustained overload rather than starting surge |
Motor circuits aren't a single calculation — they're a small system of related, distinctly-purposed sizing decisions, each governed by its own specific NEC provision.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks