Journeyman Electrician Exam (NEC)Control Devices and MotorsEasy
A technician is installing a motor control circuit that operates at 120V and is protected by a 15A overcurrent protective device. The control circuit conductors are installed in a raceway. What is the minimum size copper control circuit conductor permitted for this installation, assuming it does not extend beyond the motor starter enclosure?
- A12 AWG
- B16 AWG
- C18 AWG
- D14 AWG
Show answer & explanationAnswer & explanation
Correct answer: D. 14 AWG
According to NEC Table 430.72(B) and the associated rules, control circuit conductors are generally permitted to be smaller than 14 AWG. However, for a 15A overcurrent protective device, if the conductors do not extend beyond the motor starter enclosure, 14 AWG is permitted. If the conductors extend beyond the enclosure, 12 AWG would be required for a 15A OCPD.
Why the other options are wrong
- A. 12 AWG would be required if the conductors extended beyond the starter enclosure for a 15A OCPD.
- B. 16 AWG is permitted for OCPD up to 10A. Not applicable here.
- C. 18 AWG is permitted for OCPD up to 7A. Not applicable here.
Motor Control Circuit Conductor Sizing (Enclosure)
For motor control circuits protected by an overcurrent device, the minimum conductor size is determined by the OCPD rating, with specific allowances for smaller conductors when confined within a motor starter enclosure.
- NEC 430.72(B) and Table 430.72(B) govern sizing.
- Smaller conductors (18, 16 AWG) are allowed for lower OCPD ratings.
- 14 AWG is the minimum for a 15A OCPD within an enclosure.
- Conductors extending beyond the enclosure often require larger sizes.
Memory trick: Control Wires: Smallest gauge depends on fuse and where it goes.