Absurdly Simple Question

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Jim W in Tampa said:
Yes it would work but no not legal. What happens if the other circuit for what ever reason is not on ? Thats why its a no go. All conductors must be protected. Usually the neutral is protected by the ungrounded conductor being fused
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Jim- a neutral for a feeder does not have to be the same size as the ungrounded conductors just large enough for the load and at least as large as the egc.
 
Dennis Alwon said:
Jim- a neutral for a feeder does not have to be the same size as the ungrounded conductors just large enough for the load and at least as large as the egc.
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Yes we all know that but its allowed because it is a FEEDER and very unlikely ever come close to having a serious unbalanced load.
The simple fact is NEC says 15 amps on #14 and 20 amps on #12
It goes back to the argument of a #14 switch leg on a 20 amp circuit. Totally agree it would work but simply not allowed. We don't need to agree with NEC but we must comply.
 
Jim W in Tampa said:
Yes we all know that but its allowed because it is a FEEDER and very unlikely ever come close to having a serious unbalanced load.
The simple fact is NEC says 15 amps on #14 and 20 amps on #12
It goes back to the argument of a #14 switch leg on a 20 amp circuit. Totally agree it would work but simply not allowed. We don't need to agree with NEC but we must comply.
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Jim if you have a circuit with a known load as I described above then the neutral cannot be overloaded. Sure someone can add to it but I thought that was their problem. :). I doubt the scenario would come up in the real world.
 
Technically speaking we dont have a neutral in this circuit since its single phase. We have two conductors one grounded and one not. The current carrying conductors need to be sized accordingly. I dont think the NEC supports a smaller grounded conductor for branch circuits.
 
mikeames said:
Technically speaking we dont have a neutral in this circuit since its single phase. We have two conductors one grounded and one not. The current carrying conductors need to be sized accordingly. I dont think the NEC supports a smaller grounded conductor for branch circuits.
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Mike did you read 210.19(A)(1) except.2 that I posted. It is pretty clear.
 
Dennis Alwon said:
Mike did you read 210.19(A)(1) except.2 that I posted. It is pretty clear.
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What you are missing, Dennis, is that that exception deals only with sizing the wire. Protecting the wire is another matter. The design process is (1) Calculate the load, (2) Size the wire, and (3) Select an OCPD to protect the wire. You are talking about step (2). When you get around to step (3), you won't be legally able to select a 20 amp breaker for the situation under discussion.
 
charlie b said:
What you are missing, Dennis, is that that exception deals only with sizing the wire. Protecting the wire is another matter. The design process is (1) Calculate the load, (2) Size the wire, and (3) Select an OCPD to protect the wire. You are talking about step (2). When you get around to step (3), you won't be legally able to select a 20 amp breaker for the situation under discussion.
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Then what purpose does this entire section have. It seems worthless.
 
Dennis Alwon said:
Then what purpose does this entire section have. It seems worthless.
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I can't see it being useful on a single phase, two wire branch circuit. But perhaps on a three phase, four wire branch circuit, or even a MWBC, it could allow you to save some money on the neutral wire. For my part, I don't down size the neutral, even if the code allows me to.
 
Dennis Alwon said:
Jim if you have a circuit with a known load as I described above then the neutral cannot be overloaded. Sure someone can add to it but I thought that was their problem. :). I doubt the scenario would come up in the real world.
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All your missing is the protection of the wire. Fixed or not the wire must be protected and no not likely you ever see it unless a hack installed it.
 
charlie b said:
I can't see it being useful on a single phase, two wire branch circuit. But perhaps on a three phase, four wire branch circuit, or even a MWBC, it could allow you to save some money on the neutral wire. For my part, I don't down size the neutral, even if the code allows me to.
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Agreed. Even a down-sized neutral needs to be large enough for the maximum line-to-neutral load.
 
Jim W in Tampa said:
All your missing is the protection of the wire. Fixed or not the wire must be protected and no not likely you ever see it unless a hack installed it.
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The wiring certainly has ground fault and short circuit protection. The overload protection becomes an issue only if you go over the calculated load for the neutral- sorry grounded conductor.

I do understand what everyone is saying. I am playing a bit of devils advocate and trying to wrap myself around this section.

I also know that what goes out as 14 amps comes back as 14 amps. I don't understand why the grounded conductor would not need to be sized for the continuous load-- for that matter why does the ungrounded wire need to be sized 125% but not the grounded conductor. It seems that perhaps they should have said only for MWBC or whatever or just dropped this section altogether.
 
Dennis Alwon said:
The wiring certainly has ground fault and short circuit protection. The overload protection becomes an issue only if you go over the calculated load for the neutral- sorry grounded conductor.I do understand what everyone is saying. I am playing a bit of devils advocate and trying to wrap myself around this section.

I also know that what goes out as 14 amps comes back as 14 amps. I don't understand why the grounded conductor would not need to be sized for the continuous load-- for that matter why does the ungrounded wire need to be sized 125% but not the grounded conductor. It seems that perhaps they should have said only for MWBC or whatever or just dropped this section altogether.
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Wrong, during normal operation it would not be an issue but the utilization equipment attached to the circuit can fail in a way that it will still draw a load under the OCPD trip rating but over the grounded conductors rating.
 
Dennis Alwon said:
Now that makes the most sense but I have never heard it before.
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Me neither. I found this:

The connected wire acts to some degree as a heat sink for the breaker. That is, it helps to dissipate heat produced within the breaker. This is because the breaker?s case acts as not only an electrical but a thermal insulation also, in that it tends to retard the rate of heat transfer. This is one reason why breakers have wire size ranges marked on them. Too small a wire attached to the breaker cannot adequately aid in cooling the breaker.
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Here:

http://www.mikeholt.com/mojonewsarchive/EES-HTML/HTML/ElectricalCircuitBreakers~20030621.htm
 
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