Motors: FLC, protection, and sizing

Motor circuits break the usual rules, and exams know it. You size conductors and overload protection from the NEC table full-load current (FLC), NOT from the motor nameplate — the tables are deliberately conservative. The nameplate current is used only for sizing the overload device itself.

Motors draw enormous inrush at start — often six times running current — so short-circuit protection must be large enough to ignore starting while still catching faults. That splits protection into two separate jobs: the branch-circuit short-circuit and ground-fault device (typically an inverse-time breaker at up to 250% of FLC) handles faults and lets the motor start, while separate overload protection (typically 115–125% of nameplate FLA) protects the windings from sustained overwork.

Conductor sizing is the third number: branch-circuit conductors for a single motor are sized at 125% of the table FLC. So one motor generates three different percentages — 125% for conductors, 115–125% for overloads, up to 250% for the breaker — and exam questions exist precisely to see whether you mix them up.

Exam focus: table FLC vs. nameplate FLA, the 125% conductor rule, and why the breaker is oversized relative to the conductor. That last one feels wrong until you realize the overload relay is what actually protects the motor.

Quiz — 3 questions