Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A client is installing a new 240V, single-phase motor with a nameplate FLA (Full Load Amperes) of 25A. According to NEC Article 430.22, what is the minimum conductor ampacity required for the motor branch circuit conductors, assuming no other adjustments or corrections?
- A37.5A
- B25A
- C50A
- D31.25A
Show answer & explanationAnswer & explanation
Correct answer: D. 31.25A
According to NEC 430.22(A), branch-circuit conductors supplying a single motor shall have an ampacity not less than 125% of the motor's full-load current rating. So, 25A * 1.25 = 31.25A.
Why the other options are wrong
- A. This would be 150% of the FLA, which is incorrect for conductor sizing (but relevant for OCPD sizing in some cases).
- B. This is the motor's FLA, not the minimum conductor ampacity as required by NEC.
- C. This is 200% of the FLA, which is incorrect for conductor sizing.
Motor Branch Circuit Conductor Sizing
NEC Article 430.22(A) mandates that conductors supplying a single motor must have an ampacity of at least 125% of the motor's full-load current rating, before any adjustments or corrections.
- Minimum ampacity = 125% * Motor FLA.
- This factor accounts for motor starting currents and continuous operation.
- Applies to branch-circuit conductors for single motors.
- Further adjustments for temperature or bundling may be required.
Memory trick: Motor conductors need a 25% safety net, for continuous run, don't forget it yet!