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PV Wire Sizing, Terminal Temperature Limits, 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c), 110.14(C), 110.14(C)(1)(a) and 110.14(C)(1)(b)


Q:

Dear Doc,
A little late question ,concerning article 310 and 110.14 (c),110.14(c)(1)(a) or (C)(1)(b)
When you talk about terminal ratings,I am aware of three areas in solar where wires terminate ,combiner box ,inverter and main panel ocpd.
Are we talking here about, adjustment and correction factors ,dealing with ocpd of the solar breaker in main panel or the equipment shutoff breaker ,I am assuming these articles are referring to the main panel termination or equipment shut off termination.
This is the missing link I need to know to understand.
Appreciate the help

A:

When we are doing any wire sizing, we have to take the terminal temperature limits into consideration, whenever a wire terminates at a terminal.

This does include at a termination at a combiner box, inverter, main panel OCPD, even a wire nut.

When we do the checks for corrections factors for derating of ampacity with tables 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c) (conditions of use derating) we do not take the terminal temperature limits into consideration for that calculation.

We do take the terminal temperature limits into consideration when we are looking at the required ampacity for continuous current, which is 125% of maximum circuit current.

This means that when we check for continuous current, we take the terminal temperature into consideration.

When we check for conditions of use, we do not take the terminals or continuous current into consideration.

Let me say that one more time:

When we check for continuous current, we take the terminal temperature into consideration.

When we check for conditions of use, we do not take the terminals or continuous current into consideration.

Remember that conditions of use are the 310 tables 310.15(B)(2)(a), 310.15(B)(3)(a) and 310.15(B)(3)(c) where we reduce our ampacity due to high temperatures and greater than 3 current carrying conductors in conduit.

Good questions!

Sean White


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