CSLB C-46 Solar ContractorElectrical and Plumbing CodesHard
A solar contractor is installing a conduit containing PV array circuit conductors on a rooftop. The conduit is exposed to direct sunlight and high ambient temperatures. According to NEC Article 310.15(B)(2)(c), what additional temperature adder must be applied to the ambient temperature for conduits exposed to direct sunlight on or above a rooftop, when the conduit is less than 7/8 inch from the roof surface?
- A17°C (30°F)
- B39°C (70°F)
- C33°C (60°F)
- D22°C (40°F)
Show answer & explanationAnswer & explanation
Correct answer: C. 33°C (60°F)
NEC Article 310.15(B)(2)(c) specifies that where conduits, raceways, or cables are exposed to direct sunlight on or above rooftops, and are less than 7/8 inch from the roof surface, a temperature adder of 33°C (60°F) must be added to the ambient temperature. This accounts for the significant heat gain from solar radiation and helps prevent conductor overheating.
Why the other options are wrong
- A. 17°C (30°F) is incorrect; this figure is for other derating scenarios.
- B. 39°C (70°F) is incorrect; this figure is for other derating scenarios.
- D. 22°C (40°F) is incorrect; this figure is for other derating scenarios.
NEC Rooftop Conduit Temperature Adder
An additional temperature value (33°C/60°F) mandated by NEC 310.15(B)(2)(c) to be added to the ambient temperature for conductor ampacity calculations when conduits are mounted close to sun-exposed rooftops.
- Applies to conduits exposed to direct sunlight.
- Conduit must be less than 7/8 inch from roof surface.
- Adder is 33°C (60°F).
- Prevents conductor overheating.
Memory trick: Rooftop heat, 33 degrees to beat, or your wires will meet defeat!