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Ampacity Derating for Fire Condition 700.10

Question asked by troyk31 on Mar 3, 2020
Latest reply on Mar 20, 2020 by chiefns830

I wanted to clarify what the designer is expected to do regarding calculations to show compliance with 310.15 (B) (2) Ambient Temperature Adjustment Factors, especially during a fire condition.


This is also a requirement in NEC 700.10 (C), and (D) regarding protection/consideration of exposure to fire (and other conditions) and it’s relation to reduced ampacity and any other considerations when exposed to temperatures above what is listed in the tables in 310.15.


The requirements in Chapter 700.10 (D) address the protection of the circuits but does not address ampacity correction that may be needed..  My understanding is that when the fire test is completed the conductors are energized to illuminate a string of incandescent lamps to see if they will illuminate. This fire test does not address the ampacity required for any particular load during a fire event at elevated temperatures.


When do the  conductors need to be derated?  Even if they are installed to comply with one of methods in NEC 700.10 (C), and (D)?


Thanks for your input.