i had an electrician challenge on a question. He ran a no.12 NM-B cable to a bedroom as a home run, then ran 14 NM-B cable around the walls for Rec.outlets and lighting. He says he can fuse that circuit at 20amps. To me that would be a 15amp circuit. In table 310.16 the astrek next to the wire size sends me to 240.4(D)and says 14awg fuse at 15amps. I've read this section and cant find where it could be fused 20amps. Hopefully i made sense.
branch circuits
- Thread starter escape
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- New Jersey
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- Journeyman Electrician (retired)
Re: branch circuits
He needs to use a 15 amp OCPD for the #14 wire as specified in 240.4(D). What code section did he say allows him to do this?
He needs to use a 15 amp OCPD for the #14 wire as specified in 240.4(D). What code section did he say allows him to do this?
wanderer20001us
Senior Member
Re: branch circuits
210.19 (A) (2) prohibits what he did.
210.19 (A) (2) prohibits what he did.
- Location
- New Jersey
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- Journeyman Electrician (retired)
Re: branch circuits
I don't think that this Article 210.19(A)(2) would prohibit the installation described in the original post. According to 310.16, #14 wire is rated for 20 amps so it would comply with 210.19(A)(2) if it were protected by a 20 amp OCPD. However, as Escape mentioned, 240.40(D) limits the OCPD in this scenario to 15 amps.
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: branch circuits
Think of this: 240 is all about overcurrent protection. It is not about ampacity. The limits of 240.4(D) are limits for the overcurrent protection device. 240.4(D) does not limit the ampacity of a #12 to 20 amps. Rather, it limits the OCPD to no more than 20 amps, regardless of the ampacity of the wire. Go to 310, deal with any temperature or multiple conductor issues that may apply, and find the ampacity of the #12. If you get any ampacity between 16 and 30, you can use a 20 amp OCPD, and you cannot use anything higher (no 25 amp or 30 amp breaker, and certainly nothing higher than that).
That being said, what is the value in having 240.4(D) say anything about temperature and multiple conductors? None! You don't correct for temperature before picking an OCPD. You correct for temperature before picking a wire size. Then and only then do you look at 240, and pick the breaker rating. I might have submitted a code change to remove the last 14 words from 240.4(D).
That's a good point, and I fully agree. But it points out a missed opportunity for a code change. I wish this exchange took place a month ago. I might have submitted another change for the 2008 code (that would have made a grand total of 2).
Think of this: 240 is all about overcurrent protection. It is not about ampacity. The limits of 240.4(D) are limits for the overcurrent protection device. 240.4(D) does not limit the ampacity of a #12 to 20 amps. Rather, it limits the OCPD to no more than 20 amps, regardless of the ampacity of the wire. Go to 310, deal with any temperature or multiple conductor issues that may apply, and find the ampacity of the #12. If you get any ampacity between 16 and 30, you can use a 20 amp OCPD, and you cannot use anything higher (no 25 amp or 30 amp breaker, and certainly nothing higher than that).
That being said, what is the value in having 240.4(D) say anything about temperature and multiple conductors? None! You don't correct for temperature before picking an OCPD. You correct for temperature before picking a wire size. Then and only then do you look at 240, and pick the breaker rating. I might have submitted a code change to remove the last 14 words from 240.4(D).
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