Maximum homeruns

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peter d

peter d

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Location
New England
satcom said:
We derate the conduit to reduce problems from the effect of heating, all conduits are enclosing the conductors, and in metal conduits, we have the additional effect of not just current loading, but also the added effect of induced induction loads, and these loads can, if not derated, reach a temp hot enough to cook an egg.

It would be nice for the OP the read up and learn as much as he can about derating, it is not a cut and dried, read the table. and just do it issue.
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I understand the principle of induction. I also don't see that the NEC addresses it with regard to derating.

The inductive heating you mention is a result of isolated phase conductors being run in a metal raceway, or running the grounded conductors in a separate raceway away from the ungrounded conductors, both of which are code violations and have nothing to do with derating.
 
S

satcom

Senior Member
peter d said:
I understand the principle of induction. I also don't see that the NEC addresses it with regard to derating.

The inductive heating you mention is a result of isolated phase conductors being run in a metal raceway, or running the grounded conductors in a separate raceway away from the ungrounded conductors, both of which are code violations and have nothing to do with derating.
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The NEC does not address it directly, and it is not a result of isolated phase conductors being run in a metal raceway, or running the grounded conductors in a separate raceway away from the ungrounded conductors, it is proper wiring methods not derated, and serving loads, such as banks of ballasts, and other non liner loads.
 
C

Cold Fusion

Senior Member
Location
way north
satcom said:
The NEC does not address it directly, and it is not a result of isolated phase conductors being run in a metal raceway, or running the grounded conductors in a separate raceway away from the ungrounded conductors, it is proper wiring methods not derated, and serving loads, such as banks of ballasts, and other non liner loads.
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Okay, that sounds like you are discussing the third-harmonic neutral loading, when using a multiwire circuit on a non-linear loads, such as ballasts, or switching power supplies. If so, the NEC does discuss that: 310.15.B.4.C. Paraphrased: If the majority of the loads are nonlinear, then the neutral is considered a current carrying conductor. So the circuit now has 4 CCC instead of 3.

I have never heard of this non-linear load causing a metalic conduit to heat up more that just the CCC heat it up. AFAIK the NEC doesn't discuss that even indirectly. Do you have any data to support this?

cf
 
e57

e57

Senior Member
Location
San Francisco, CA
peter d said:
I understand the principle of induction. I also don't see that the NEC addresses it with regard to derating.

The inductive heating you mention is a result of isolated phase conductors being run in a metal raceway, or running the grounded conductors in a separate raceway away from the ungrounded conductors, both of which are code violations and have nothing to do with derating.
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It's actually a major part of the calculations that make up the tables of 310 and the derating table included - which make certain assumptions.... I did a bunch of internet searches about the tables and who wrote the formulas that make them a while back. The Gent - of whose name I can not remember now devised the calculations for underground parallel conduits and the inductive heating between them...
 
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