# ART 300.20 Hot wires in metal pipe (induction?)



## Shockdoc (Mar 4, 2010)

ROCKDOG said:


> I have a question about running multiple ungrounded conductors and their returning switchlegs through a pipe by themselves. Between a central lighting j box and a 6 gang switch bank. Should a grounded conductor be pulled in the same pipe to prevent heating even though no current would be travelling on the neutral since its just going to a bunch of s pole switches?


What difference would a grounded conductor make ? How many wires, how many phases, what ga. wire, what size conduit ?


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## McClary’s Electrical (Feb 21, 2009)

Shockdoc said:


> What difference would a grounded conductor make ? How many wires, how many phases, what ga. wire, what size conduit ?


 

A grounded conductor being ran with the unrounded cancels out the magnetic field. But, in his case, they are switch loops, so one wire under load always has an opposing wire running the opposite direction. Same cancellation effect as running a grounded conductor with them.

Although, the new code cycle calls for a noodle in the switch box anyway, but he doesn't need it for induction reasons.


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## RIVETER (Sep 26, 2009)

ROCKDOG said:


> I have a question about running multiple ungrounded conductors and their returning switchlegs through a pipe by themselves. Between a central lighting j box and a 6 gang switch bank. Should a grounded conductor be pulled in the same pipe to prevent heating even though no current would be travelling on the neutral since its just going to a bunch of s pole switches?


 And, the hot and the return would be in sync...no difference of potential. No heating.


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## Shockdoc (Mar 4, 2010)

mcclary's electrical said:


> A grounded conductor being ran with the unrounded cancels out the magnetic field. But, in his case, they are switch loops, so one wire under load always has an opposing wire running the opposite direction. Same cancellation effect as running a grounded conductor with them.
> 
> Although, the new code cycle calls for a noodle in the switch box anyway, but he doesn't need it for induction reasons.


Agreed, his induction sounds more like a combination of conduit fill/ derating/ harmonics. Current is flowing bothways, a noodle would do absolutely nothing other that exist.


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## ROCKDOG (Sep 14, 2011)

I dont have print in front of me. at least 2 of 3 phases if not all three. I think 3 hots, six switchlegs, 3/4 pipe. #12 AWG. not sure what difference a grounded conductor would make. I just remembered something from trade school. they said dont run a single hot in a pipe by itself without neutral. It may cause inductive heating. so I read 300.20 "group phase conductors and, whre used grounded and EGC together." maybe this is not "whre used."


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## ROCKDOG (Sep 14, 2011)

thanks guys. im not up on such arcane wisdom as yourselves. I didn't really see anything wrong with that install since i've seen it existing on a much larger scale. just wondering. . .


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## Dennis Alwon (May 9, 2009)

That is true you cannot run the neutral separately from the hot in metal conduit as it will cause excessive heating. A switch loop does not apply to that situation.

BTW, my sister lives in Longmont.


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## Shockdoc (Mar 4, 2010)

ROCKDOG said:


> I dont have print in front of me. at least 2 of 3 phases if not all three. I think 3 hots, six switchlegs, 3/4 pipe. #12 AWG. not sure what difference a grounded conductor would make. I just remembered something from trade school. they said dont run a single hot in a pipe by itself without neutral. It may cause inductive heating. so I read 300.20 "group phase conductors and, whre used grounded and EGC together." maybe this is not "whre used."


That's only when pushing current one way in a metallic raceway. 9 current carrying conductors, #12, good for 15 amps ea. What kind of fixtures are they controlling ? I have seen induction heat from high bay lighting on 208 volts, this ones got my curiosity.


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## ROCKDOG (Sep 14, 2011)

feeding mostly fluorescent 2x4 troffers. nothing special. a couple of 2 lamp t8 strips, coulpe of track lights. not really a big load. small gas station C Store. 


Oh, I've visited Chapel Hill before. Long time ago. Star Trek 5 in theatre. Ha.


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## ROCKDOG (Sep 14, 2011)

9 current carriers, 70%. THHN 90 degree 30 Amp X .7 = 21 amp right?. . . 


ART 110.14 (C) . . . "conductors with temp. ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both."


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## RIVETER (Sep 26, 2009)

ROCKDOG said:


> I dont have print in front of me. at least 2 of 3 phases if not all three. I think 3 hots, six switchlegs, 3/4 pipe. #12 AWG. not sure what difference a grounded conductor would make. I just remembered something from trade school. they said dont run a single hot in a pipe by itself without neutral. It may cause inductive heating. so I read 300.20 "group phase conductors and, whre used grounded and EGC together." maybe this is not "whre used."


If you are still in school, ask your instructor how, in the situation you describe, a current could flow in the pipe if the neutral of the system was properly grounded at the proper location.


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## guest (Feb 21, 2009)

RIVETER said:


> If you are still in school, ask your instructor how, in the situation you describe, _*a current could flow in the pipe if the neutral of the system was properly grounded at the proper location.*_












WTF? Where do you come up with some of the things you post? Do you even read the threads? What does this have to do with the OP's situation? :laughing:

The proper answers have already been given...currents returning on a switchleg cancel out the currents on the line sides. In other situations the return current on the neutral will also provide the cancellation.


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## RIVETER (Sep 26, 2009)

mxslick said:


> WTF? Where do you come up with some of the things you post? Do you even read the threads? What does this have to do with the OP's situation? :laughing:
> 
> The proper answers have already been given...currents returning on a switchleg cancel out the currents on the line sides. In other situations the return current on the neutral will also provide the cancellation.


I take no offense. If I looked like that I'd be upset too.


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## RIVETER (Sep 26, 2009)

mxslick said:


> WTF? Where do you come up with some of the things you post? Do you even read the threads? What does this have to do with the OP's situation? :laughing:
> 
> The proper answers have already been given...currents returning on a switchleg cancel out the currents on the line sides. In other situations the return current on the neutral will also provide the cancellation.


Just to clear the air...yes, I read the original post. I don't read all of the subsequent posts of the respondents in order to form my opinion or post. I am not always right in my posts but I can live with that...no one has died from a post...in error. What I can say for sure is that persons on a forum are typically here to learn...myself included. Maybe you could calm down a little. It is in your best interest. I know a handful of people who are out of work because of the poor economy. I know a just a few who are out of work because of their MOUTH. And I mean that in a "loving" way.


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