CSLB C-46 Solar ContractorSolar Thermal System InstallationMedium
A solar thermal installer is connecting a new circulation pump to the electrical supply for a 240V, 60Hz system. The pump's nameplate indicates a full load current (FLA) of 1.5 Amperes. Assuming typical residential wiring practices and a continuous load, what is the minimum gauge wire required for this circuit, considering the NEC table for ampacity?
- A14 AWG
- B12 AWG
- C18 AWG
- D16 AWG
Show answer & explanationAnswer & explanation
Correct answer: A. 14 AWG
For continuous loads, the circuit must be sized for 125% of the FLA. 1.5A * 1.25 = 1.875A. The smallest common wire size for general purpose circuits is 14 AWG, rated for 15A, which is well above the calculated requirement. While 18 AWG or 16 AWG might technically carry 1.875A, NEC typically mandates 14 AWG as the minimum for lighting and general power branch circuits in residential applications.
Why the other options are wrong
- B. 12 AWG is rated for 20 amps and is overkill for a 1.875A continuous load, though it would be safe.
- C. 18 AWG is generally too small for permanent residential wiring and typically used for low-voltage or control circuits.
- D. 16 AWG is also generally considered too small for permanent residential power circuits, though it can carry more than 1.875A.
Wire Sizing (Continuous Load)
Selecting the correct wire gauge for electrical circuits, especially for continuous loads, to prevent overheating and ensure compliance with electrical codes.
- Continuous loads require 125% ampacity rating
- NEC tables specify ampacity for wire gauges
- 14 AWG is common minimum for residential branch circuits
Memory trick: Pump's current, continuous, then add a quarter; wire it right, or face the fire starter.