I have searched the web site and found various topics on this subject but none answered my question I have. Here goes. I have a 3 phase 4 wire wye system 120/208. If I take a 12/2 to feed convenience receptacles would I count the neutral? What if I ran 3 phase conductors (a,b,c) with 1 neutral sharing the neutral for convenience outlets would I count the neutral? I have read article 315 but am still confused. Help.
neutral as current carrying conductor
- Thread starter tkirk911
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ryan_618
Senior Member
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- Salt Lake City, Utah
Re: neutral as current carrying conductor
Question one, yes.
Question 2, depends on the balance of the load. See 310.15(B)(4).
Question one, yes.
Question 2, depends on the balance of the load. See 310.15(B)(4).
- Location
- Illinois
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- retired electrician
Re: neutral as current carrying conductor
For question 2 the neutral is not a current carrying conductor unless the major portion of the laod is nonlinear.
Don
For question 2 the neutral is not a current carrying conductor unless the major portion of the laod is nonlinear.
Don
stew
Senior Member
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- federal way,washington
Re: neutral as current carrying conductor
hey ryan I thought you counted it for fill but not for purposes of derating for ampacity calc.?
hey ryan I thought you counted it for fill but not for purposes of derating for ampacity calc.?
ryan_618
Senior Member
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- Salt Lake City, Utah
Re: neutral as current carrying conductor
Hi Stew. You might be thinking of the EGC, which is, just as you said, included for fill but not not for ampacity adjustment. With the grounded conductor, it also is included for fill, but as far the ampacity adjustment goes...well, sometimes it is and sometimes it isn't.
Hi Stew. You might be thinking of the EGC, which is, just as you said, included for fill but not not for ampacity adjustment. With the grounded conductor, it also is included for fill, but as far the ampacity adjustment goes...well, sometimes it is and sometimes it isn't.
hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: neutral as current carrying conductor
310.15(B)(4)(b) requires the neutral of a 4-wire "Y" system to be counted. And this is a "Y" system?
But is this question for race-way or box-fill count?
310.15(B)(4)(b) requires the neutral of a 4-wire "Y" system to be counted. And this is a "Y" system?
But is this question for race-way or box-fill count?
- Location
- Illinois
- Occupation
- retired electrician
Re: neutral as current carrying conductor
Wayne,
The section you cite only requires the neutral of the 3 phase 4 wire system to be counted as a current carrying conductor when you are using 2 phases and the neutral. When you are using all 3 phases and the neutral, it is a current carrying conductor only when the major portion of the load in nonlinear.
Don
Wayne,
The section you cite only requires the neutral of the 3 phase 4 wire system to be counted as a current carrying conductor when you are using 2 phases and the neutral. When you are using all 3 phases and the neutral, it is a current carrying conductor only when the major portion of the load in nonlinear.
Don
Re: neutral as current carrying conductor
tkirk911,
Here's the section of the NEC everyone is referencing. Hope it helps.
(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.
tkirk911,
Here's the section of the NEC everyone is referencing. Hope it helps.
(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.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: neutral as current carrying conductor
Whoops I was leaving out the two when I read it. As with out a load on the third phase there would only be three current caring conductors. Thank's Don sometimes I tend to read too fast.
Whoops
I was leaving out the two when I read it. As with out a load on the third phase there would only be three current caring conductors. Thank's Don sometimes I tend to read too fast. jeffhornsby
Member
- Location
- Destin, FL
Re: neutral as current carrying conductor
You only count the neutral as a current carrying conductor if one the circuits is non-linear
You only count the neutral as a current carrying conductor if one the circuits is non-linear
Re: neutral as current carrying conductor
Bajan, a grounded conductor can carry the same current as the ungrounded conductor in a two wire circuit.
In a "Wye" configuration the grounded conductor can actually have more current flowing than any one ungrounded conductor in a multi wire circuit comprised of non-linear loads.
Roger
[ June 26, 2004, 11:47 AM: Message edited by: roger ]
Bajan, a grounded conductor can carry the same current as the ungrounded conductor in a two wire circuit.
In a "Wye" configuration the grounded conductor can actually have more current flowing than any one ungrounded conductor in a multi wire circuit comprised of non-linear loads.
Roger
[ June 26, 2004, 11:47 AM: Message edited by: roger ]
Re: neutral as current carrying conductor
Roger i do agree with your illustration but the potential is different when dealing with the neutral. You will get a full potential when reading across a phase and a neutral or earth but between Neutral and earth there is an extremely small potential
Roger i do agree with your illustration but the potential is different when dealing with the neutral. You will get a full potential when reading across a phase and a neutral or earth but between Neutral and earth there is an extremely small potential
- Location
- Massachusetts
Re: neutral as current carrying conductor
What does the potential between neutral and earth have to do with the neutral being counted as a current carrying conductor?
Re: neutral as current carrying conductor
Hello Bob, Bajan I must also ask, what does potential differences have to do with the heating associated with current flow in a grounded conductor?
Consider this, same potential and more current.
The grounded conductor can be overloaded with no help from additional potential, the voltage is the same and has already dropped across the load/s but current must return to source.
Roger
[ June 26, 2004, 12:38 PM: Message edited by: roger ]
Hello Bob, Bajan I must also ask, what does potential differences have to do with the heating associated with current flow in a grounded conductor?
Consider this, same potential and more current.
The grounded conductor can be overloaded with no help from additional potential, the voltage is the same and has already dropped across the load/s but current must return to source.
Roger
[ June 26, 2004, 12:38 PM: Message edited by: roger ]
Re: neutral as current carrying conductor
I really dont understand the discussions here. The situation presented in the sketch shows 20A flowing in a conductor but would nt the cable be already sized to allow the currents in the circuit and would the breaker control this flow .
What I got from the ? was if he had to count the neutral as a current carrying cable . If he already has his cables sized why would he consider it that way
I really dont understand the discussions here. The situation presented in the sketch shows 20A flowing in a conductor but would nt the cable be already sized to allow the currents in the circuit and would the breaker control this flow .
What I got from the ? was if he had to count the neutral as a current carrying cable . If he already has his cables sized why would he consider it that way
Re: neutral as current carrying conductor
In a linear "multi-wire circuit" the grounded conductor does not add to the the heating effects in that it can theoretically be neutral, in otherwords, not have any current flowing at all.
Note: The illustrations are showing single phase and three phase Wye's are a little different, but in a 4 wire linear "multi-wire circuit" the same can apply.
Roger
The size of the conductor and whether it is sized for the load is not the question here, it is the heating effect the current on the conductor will have inside of a conduit.
In a linear "multi-wire circuit" the grounded conductor does not add to the the heating effects in that it can theoretically be neutral, in otherwords, not have any current flowing at all.
Note: The illustrations are showing single phase and three phase Wye's are a little different, but in a 4 wire linear "multi-wire circuit" the same can apply.
Roger
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