A motor control circuit operates at 120V and is protected by a 10A fuse. The control circuit conductors are routed in a raceway with power circuit conductors supplying a 30A motor branch circuit. According to NEC 430.72(B), what is the minimum allowable size for the control circuit conductors?
- A18 AWG
- B12 AWG
- C14 AWG
- D16 AWG
Show answer & explanationAnswer & explanation
Correct answer: C. 14 AWG
NEC 430.72(B) specifies that control circuit conductors that extend beyond the motor control enclosure must not be smaller than 14 AWG unless protected by an overcurrent device rated at not more than 10 A, in which case 18 AWG or 16 AWG conductors are permitted. However, in this scenario, the control circuit conductors are in a raceway with power circuit conductors protected at 30A. NEC 430.72(B) Exception No. 1 states that if the control circuit conductors are in the same raceway as the power circuit conductors, and the power circuit overcurrent device is rated over 20A, the control conductors must not be smaller than 14 AWG.
Why the other options are wrong
- A. 18 AWG is permitted for control circuits protected at 10A or less, but not when in a raceway with power conductors protected over 20A.
- B. 12 AWG would be permitted, but 14 AWG is the minimum required size in this specific scenario.
- D. 16 AWG is permitted for control circuits protected at 10A or less, but not when in a raceway with power conductors protected over 20A.
Motor Control Conductor Sizing (NEC 430.72)
NEC Article 430.72 dictates the minimum size for motor control circuit conductors based on their overcurrent protection and proximity to power circuit conductors to ensure mechanical strength and adequate current-carrying capacity.
- Generally, control circuit conductors must not be smaller than 14 AWG.
- Smaller conductors (16 AWG or 18 AWG) are permitted if the control circuit is protected by an overcurrent device rated 10A or less.
- An exception applies when control conductors are in the same raceway as power conductors, requiring larger sizes if the power circuit protection exceeds 20A.
Memory trick: Control wires are small, but they need big protection if they're with the big guys.