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Joined: Nov 2007
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KJay,
How does 240.4(D) not apply? To be honest, I’m not sure that it doesn’t. I may be over thinking this, but what I see is that 310.16 is allowable conductor ampacity and 240.4[D] is overcurent protection. Two different things, IMO anyway.
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Joined: Nov 2000
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Yes they are two different things and that is a fact that is often missed. This is a very important issue when applying the provisions of 240.4(B). You just have to remember that 240.4(B) does not change the ampacity of the conductor...it just permits the use of an over sized OCPD.
Last edited by resqcapt19; 11/12/10 09:31 AM.
Don(resqcapt19)
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Okay, it seems clear to me again that 240.4[D] would apply as usual here. Not sure why it wasn’t registering with me regarding neutral condutors.
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Joined: Jul 2004
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If you believe 240.4(D) is overload protection as opposed to short circuit protection, it clearly applies to the neutral. What goes in comes out the other end according to Mr Kirchoff.
Greg Fretwell
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My AHJ makes life simple: #12 is the minimum conductor permitted on all commercial construction -- to include Romex if commercial.
Tesla
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If you believe 240.4(D) is overload protection as opposed to short circuit protection, it clearly applies to the neutral. What goes in comes out the other end according to Mr Kirchoff. I agree that it also includes the neutral, but even the NEC’s own description of a branch circuit could be seen as a little vague. Art.100 defines a branch circuit is defined as “the circuit conductors between the final overcurrent device protecting the circuit and the outlet[s].” I think it is assumed to include a grounded [neutral] conductor, but may have been intentionaly left out since not all branch circuits use a neutral.
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If the overcurrent protection rules in Article 240 apply to the neutral, how can we size the neutral based on the neutral current as permitted for feeders? The only requirement for the feeder neutral size is the larger of what is required for the load or the size of the required EGC for the circuit. This often results in a neutral that is really only protected by the design calculations, not by the ungrounded conductor OCPD.
Yes, I know that I said that the rules in 240 apply to the neutral in an earlier post, but there are issues with that when we are talking about feeder circuits.
Don(resqcapt19)
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If the overcurrent protection rules in Article 240 apply to the neutral, how can we size the neutral based on the neutral current as permitted for feeders? The only requirement for the feeder neutral size is the larger of what is required for the load or the size of the required EGC for the circuit. This often results in a neutral that is really only protected by the design calculations, not by the ungrounded conductor OCPD.
Yes, I know that I said that the rules in 240 apply to the neutral in an earlier post, but there are issues with that when we are talking about feeder circuits. Okay, so now I guess this indirectly seems to bring back the issue I was struggling with earlier. If we know that neutral current carrying capacity is not based directly on the rating of overcurrent protection for feeders and services, would this not also apply to all branch circuit neutral conductors as well? Especially with regard to the situation covered in 240.4[D] for #14 conductors being used as a neutral for 20A branch circuits.
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The only time you can downsize a neutral is when there is a significant amount of line to line load. That will not be the case on a 120v branch circuit. If you have a 120v branch circuit 240.4(D) applies to the neutral too in my opinion.
Greg Fretwell
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Greg,
I am aware that it would be a very rare case where you could downsize a branch circuit neutral, but my question was about a feeder neutral that is permitted to be downsized based on the load calculations. If the rules in Article 240 require overcurrent protection of the neutral, how can we downsize it?
Don(resqcapt19)
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