(c) Installations Outdoors in Direct Sunlight.

Where feeders or branch-circuits are installed in raceways out-doors on rooftops that are exposed to direct sunlight, the ampacities of Tables 310.16 and 310.18 shall be derated by a factor corresponding to an outdoor ambient temperature, plus 17°C (30°F). [ROP 6–45]

6-45 Log #2721 NEC-P06
(Table 310-16, Table 310.17, Table 310.18, Table 310.19)

Final Action: Accept in Principle in Part
Submitter: Travis Lindsey, Travis Lindsey Consulting Services

Recommendation:

Add footnote to bottom of all tables cited, as follows:

Where conductors are installed within conduits and exposed outdoors to direct sunlight, add 30 F (17 C) to the expected maximum outdoor temperature to determine the ambient temperature.

Substantiation:

Recent experimentation shows that a significant temperature rise can be expected for any conductor within a conduit installed outdoors in direct sunlight.

Data indicates that a rise of 30 F (17 C) can be expected for bright metal conduits in direct sun.

Where this temperature rise is disregarded it could lead to overloaded conductors.

Currently NEC does not address temperature rise from solar exposure.

Panel Meeting Action: Accept in Principle in Part

Add a new 310.15(B)(2)(c) to read as follows:

"Installations Outdoors in Direct Sunlight.

Where feeders or branch-circuits are installed in raceways outdoors on rooftops which are exposed to direct sunlight, the ampacities of Tables 310.16 and 310.18 shall be derated by a factor corresponding to an outdoor ambient temperature, plus 17 degrees C."

Panel Statement:

The panel notes that this information does not apply to Tables 310.17 or 310.19.

The revised wording meets the intent of the submitter, and the new text is more appropriate in a new 310.15(B)(2)(c) rather than in a footnote.

Number Eligible to Vote: 11

Affirmative: 9 Negative: 2 Ballot Results:

Explanation of Negative:

KOMASSA: The submitter's substantiation does not adequately distinguish conduits directly on the roof surface vs supported some
distance above the roof. The tests conducted were not thorough in that they were conducted in Las Vegas but not also in a northern climate. Test data shows a 30°F temperature differential during 3-4 afternoon hours but does not present evidence of degradation of conductor insulation.

The submitter has supplied a detailed technical report, however, the test method is not an approved ANSI or NEMA test procedure for determining conductor derating due to direct sunlight on the raceway.

LIGGETT: This proposal should have been rejected. The testing was not conducted on all conduit installation methods on rooftops.

Not all conduits are installed within 1/2 in. of the rooftop. Conduits installed a distance greater than 1/2 in. may not be impacted as the ones tested. Sufficient testing has not been performed and test data has not been provided to require the change for all conduits on rooftops where exposed to direct sunlight. The wording proposed by the panel would require derating where it is unnecessary.