mixing wire sizes

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Question all,
Here's the situation. thinking of running a branch ckt off an existing outlet. this existing outlet in not overloaded nor will it be after running the branch ckt. branch ckt will feed a small low amp(about 3a) exhaust fan operated by a pull chain. would like to run 14-2 nm from existing outlet for exhaust fan but the existing outlet is wired with 12-2 fused by a 20 amp breaker. I'm thinking (safey wise) that under worst case senario, if some overheating occurred the 14-2 wire would give in thermally before the 12-2 and breaker therefore mixing 14-2 & 12-2 in this situation an not kosher. someone out there know the NEC for this. couldn't find anything about this in my ref book.


Senior Member
Re: mixing wire sizes

I see this situation come up alot. 210.20(B) refers you to 240.4. Most times, I see this come up when the circuit is #12 wire, protected by 20-amp OCD and feeding recpetacles and lighting outlets. The assumption is that a #14 can be brought from the switch to the single lighting outlet. The lighting outlet will never draw more than the 15-amp capability of the #14, so there should be no problem. What happens next, is someone comes along and adds three more lights. Then they re-wire the lighting outlet to always hot and install ceiling fans, and so on. I feel this is why code has made this cleary incompliant. Besides, the difference in running 12/2 and 14/2 is about 20 cents. Except in new construction where allowed, on service calls, don't even bother with 14 wire. Why use the minimium?
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