Free Steak Dinner Bet - please help

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superdave02

superdave02

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I am here in Louisiana working on some storm damage and somebody is telling me that you can take your parallel conductors and stuff all of a phase in one conduit B phase and one conduit C phase and one conduit and the neutral in one conduit is this nonsense or what?? It’s hot we’re working hard and I want my steak dinner tonight!
 
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Definitely not all phases need to be run together in same conduit neutral included

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We are talking about NEC installations. He’s is saying pvc. I will check out the above referenced code article
 
superdave02 said:
We are talking about NEC installations. He’s is saying pvc. I will check out the above referenced code article
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Yes, it is allowed in non ferrous raceways and can be a better installation at times.

Roger
 
Dang. I bet we can’t find a steak place anyway. Sorry I’ve never installed like that. Sad face
 
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Yes. Basically the reason for running all phases together is to cancel the magnetic fields produced by current flow. If you have ferrous raceways, these magnify the magnetic fields, and can basically turn an isolated phase installation into a transformer where the raceway acts as a shorted secondary.

IMHO if you have non-ferrous raceways you might be kosher with the code, but I'd be leery of an 'isolated phase' installation in anything except non-metallic raceways if the currents are large.

-Jon
 
Don't give up on your steak yet.. 300.3(B)(1) Exception is where you are allowed to run the same phases, etc in a non-ferrous conduit BUT there is a reference to 300.20 which effects metallic enclosures such as panels. Check that out.
 
The legendary iwire posted about a 480V service in steel conduit that was installed 'isolated phase', and proceeded to burn up. I've not been able to find this post.

-Jon
 
The 300.3(B)(1) Exception allows nonmetallic raceways for underground isolated phase installations. Therefore raceways which are nonferrous but are still metallic would not meet the conditions of this exception. As winnie indicated, ferrous raceways would be even worse than nonferrous metallic ones. They would have additional heating from hysteresis losses under the presence of magnetic fields, and they'd also increase the inductive reactance of the enclosed conductors because of the high "permeability" of iron.
 
synchro said:
The 300.3(B)(1) Exception allows nonmetallic raceways for underground isolated phase installations. Therefore raceways which are nonferrous but are still metallic would not meet the conditions of this exception...
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Saw the results of an isolated phase installation where the contractor had installed metallic elbows at the underground changeover from horizontal to vertical. The blowtorch effect destroyed the utility padmount transformer low voltage compartment.
 
winnie said:
Yes. Basically the reason for running all phases together is to cancel the magnetic fields produced by current flow. If you have ferrous raceways, these magnify the magnetic fields, and can basically turn an isolated phase installation into a transformer where the raceway acts as a shorted secondary.

IMHO if you have non-ferrous raceways you might be kosher with the code, but I'd be leery of an 'isolated phase' installation in anything except non-metallic raceways if the currents are large.

-Jon
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I see the raceway as a single turn inductor core, not a transformer with a shorted secondary. Heating in the conduit is the result of hysterisis losses, not current flow.

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GoldDigger said:
I see the raceway as a single turn inductor core, not a transformer with a shorted secondary. Heating in the conduit is the result of hysterisis losses, not current flow.

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That is a good point, though I think it is fair to say that both aspects are important.

Ferrous conduit will act like a core and you will see hysteresis losses. But if the structure of the conduit is such that it is connected at both ends, then you have a conductive loop acting as a shorted turn.

-Jon
 
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