Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A client requests a new dedicated 120V circuit for a hot tub pump with a nameplate rating of 18A. The circuit will be run through a conduit in the ground for 75 feet. The electrician plans to use copper conductors. What is the minimum required ampacity for the branch circuit conductors, considering NEC requirements for continuous loads?
- A25A
- B20A
- C18A
- D22.5A
Show answer & explanationAnswer & explanation
Correct answer: D. 22.5A
A hot tub pump operating for extended periods is considered a continuous load. For continuous loads, the conductors must have an ampacity of at least 125% of the load current. Therefore, 18A * 1.25 = 22.5A. The conductor must be sized to carry at least 22.5A.
Why the other options are wrong
- A. Incorrect; while 25A would be sufficient, 22.5A is the minimum calculated ampacity.
- B. Incorrect; 20A is a common breaker size, but the conductor ampacity must meet the 125% requirement first.
- C. Incorrect; this is the nameplate current, but continuous loads require a 125% factor for conductors.
Conductor Sizing for Continuous Loads
Conductors supplying continuous loads (operating for 3 hours or more) must be sized to have an ampacity of not less than 125% of the continuous load current.
- Applies to feeders and branch circuits.
- NEC 210.19(A)(1) for branch circuits, 215.2(A)(1) for feeders.
- This factor prevents overheating of conductors under prolonged operation.
Memory trick: For continuous current, conductors need 125% more flow capacity.