Which standard is used to determine the motor branch circuit fuse size?

• A. NEC Tables
• B. NEMA standards
• C. Factory Mutual
• D. Motor nameplate current

Answer: (A)

Sizing motor branch-circuit protection is based on the National Electrical Code. The NEC provides tables that convert a motor’s full-load current, which you find on the motor’s nameplate, into the correct fuse size. You use the nameplate current as the input data for these NEC tables to determine appropriate short-circuit/overload protection without nuisance tripping. Other standards or data sources aren’t the authoritative reference for fuse sizing on motor circuits—the NEC tables are. So the key point is that fuse size is determined using the NEC tables, with the motor’s nameplate current serving as the essential input.