Which data on a motor nameplate determines the maximum size of the overcurrent device for a 3-phase motor?

Which data on a motor nameplate determines the maximum size of the overcurrent device for a 3-phase motor?

• A. horsepower
• B. voltage
• C. FLA and code letter
• D. enclosure type

Answer: (C)

Sizing motor overcurrent protection hinges on two pieces of information shown on the nameplate: the full-load current (FLA) and the code letter. The FLA tells you how much current the motor typically draws when running at its rated load. The code letter encodes the motor’s starting and running characteristics and, when used with the FLA, NEC tables translate that pair into the maximum size of the short-circuit/overcurrent protective device (fuse or breaker) allowed for that motor. This pairing ensures the device will trip fast enough to protect conductors and windings in a fault, while not nuisance-tripping during normal starting. Horsepower, voltage, and enclosure type aren’t the data the NEC uses by themselves to determine that maximum OCPD. Horsepower is a mechanical rating, voltage affects current but the actual running current is already captured by FLA, and enclosure type affects protection and installation considerations but does not by itself set the OCPD size.

Sizing motor overcurrent protection hinges on two pieces of information shown on the nameplate: the full-load current (FLA) and the code letter. The FLA tells you how much current the motor typically draws when running at its rated load. The code letter encodes the motor’s starting and running characteristics and, when used with the FLA, NEC tables translate that pair into the maximum size of the short-circuit/overcurrent protective device (fuse or breaker) allowed for that motor. This pairing ensures the device will trip fast enough to protect conductors and windings in a fault, while not nuisance-tripping during normal starting.

Horsepower, voltage, and enclosure type aren’t the data the NEC uses by themselves to determine that maximum OCPD. Horsepower is a mechanical rating, voltage affects current but the actual running current is already captured by FLA, and enclosure type affects protection and installation considerations but does not by itself set the OCPD size.