How NEMA motor starter sizes work

Picking a starter without overbuying or cooking contacts

Where the numbers live. NEMA starter ratings come from NEMA ICS 2, and every manufacturer prints a selection table in its catalog. This page explains how the size system works and how to use those tables; it does not reproduce the ratings. Confirm your selection on the specific product data.

A NEMA starter size is a contactor rating. Each size carries a maximum horsepower at each standard voltage and a continuous current rating. Because horsepower converts to fewer amps at higher voltage, the same size handles more horsepower at 460 V than at 208 or 230 V. The system has a lot of margin built in, which is why NEMA gear is forgiving in the field.

Worked selections. A 7.5 hp, 460 V pump with normal start/stop fits a Size 1, commonly rated to 10 hp at 460 V. A 20 hp, 460 V fan outgrows Size 1 and lands on a Size 2, commonly rated to 25 hp at 460 V. Change either motor to 208 V, or put it on a jog-heavy conveyor, and re-check — you are likely a size higher.

IEC is not wrong, just tighter. IEC contactors are rated in amps for a utilization category, so they are picked closer to the actual load. That makes them compact and cheap, but a contactor chosen by its AC-3 (normal start) rating will wear out fast on an inching application that needs AC-4.

Starter size is only one piece of the motor circuit. Size the conductors, breaker, and overloads with the motor branch-circuit protection guide, get running current from the motor full-load current chart guide, and pick the enclosure with NEMA enclosure types. Field PM tracks submittals and equipment so the starter on site matches the one on the schedule.