Published June 13, 2026
Here's something that confuses a lot of folks: the motor sitting in front of you has a nameplate with its actual current draw printed right on it — so why does the NEC have you look up a different number in a table instead? Turns out, both numbers matter, just for different things.
Why the split? The table values are standardized and intentionally conservative across the range of motors built for a given horsepower and voltage. If that motor ever gets swapped out for a different brand or model — which happens all the time in maintenance — the conductors and circuit protection sized from the table are still valid, even though the new motor's nameplate FLA might be slightly different.
Branch circuit conductors supplying a single continuous-duty motor must have an ampacity of at least 125% of the table FLC. Example: a 10 HP, 230V three-phase motor has a table FLC of 28A. 28 × 1.25 = 35A minimum conductor ampacity — which lands you on a 10 AWG conductor (rated 35A at 75°C per Table 310.16).
For branch-circuit short-circuit and ground-fault protection using a standard inverse-time circuit breaker, the maximum size is 250% of the table FLC, rounded up to the next standard breaker size per NEC 240.6(A) when the result doesn't land on a standard size.
Using the same 28A motor: 28 × 2.50 = 70A. Since 70A happens to be a standard breaker size, that's your answer. (Other protective device types have different percentages — 800% for instantaneous-trip breakers, 300% for non-time-delay fuses, 175% for dual-element time-delay fuses — but inverse-time breakers at 250% are the most common in the field.)
If you're used to sizing breakers for general loads, motor circuits can look backwards at first: a 10 AWG conductor (35A) protected by a 70A breaker. This is intentional. The breaker at 250% is sized to ride through the motor's inrush current (which can be 6-8× FLA for a fraction of a second at startup) without nuisance tripping — it's there for short-circuit/ground-fault protection, not overload protection. The overload protection device (separate from the breaker, sized from the nameplate FLA at closer to 115-125%) is what actually protects the conductor and motor from sustained overcurrent.
When sizing a motor circuit, the table FLC — not the nameplate — drives your wire size and branch-circuit breaker. Save the nameplate FLA for the overload protection setting. Mixing these up is one of the most common Article 430 mistakes, and it's an easy one to avoid once you know which number goes where.
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