derating

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Re: derating

I read the NEC and I do not really understand what it is telling me because I dont know what a wye connected system is and how you tell if you have one.
 
Re: derating

when counting conductors you have to add the ungrounded conductors as well as the grounded conductors,That is why when you have more than 4 2 wire cable assys in less than 24 ins. derating is a concern.
 
Re: derating

cousinles
If you use multiwire circuits the neutral carries only the unbalanced current from other conductors of the same circuit then you don't have to count the neutral.

By Allen: cable assys in less than 24 ins. derating is a concern.
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Did you mean more than 24"?
 
Re: derating

Originally posted by cousinles: when derating your wire for conduit fill do you have to count your neutral wire as a current carrying conductor
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You are talking about two different subjects. Conduit fill is all about the cross-sectional area of the wires, as a percentage of the cross-sectional area of the conduit. It does not matter whether any given wire carries current or not. If the wire is there, it counts.

The question of counting the neutral as being a current-carrying wire only comes into play when you are derating because the number of current-carrying wires exceeds three.
 
Re: derating

my question do you count the neutral wire as a current carrying conductor when deraiting wire? If you have three circuits sharing a neutral is this three current carrying conductors or four? according to code you do not have to start derating until you have four current carrying conductors in a conduit. I am not asking anything about conduit fill I am sorry if it sounded that way. The way I understood the code was sometimes you have to count the neutral and sometimes you don't I don't understand when you count it and when you don't.
 
Re: derating

As Peter said, your answer is in 310.15(B)(4).

(4) Neutral Conductor

(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).

(b) In a 3-wire circuit consisting of two phase wires and the neutral of a 4-wire, 3-phase, wye-connected system, a common conductor carries approximately the same current as the line-to-neutral load currents of the other conductors and shall be counted when applying the provisions of 310.15(B)(2)(a).

(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral shall therefore be considered a current-carrying conductor.
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Now, don't take this wrong, but you list yourself as an electrician, recognizing a Wye connected system is pretty basic.

Wye.gif


Roger

[ October 31, 2005, 07:18 PM: Message edited by: roger ]
 
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