RUNNING PARALELL WIRES IN EMT

[Duke1317]

MAY I RUN 3-500KCMIL FOR ONE PHASE EXAMPLE:
3-4" EMT IN PARALELL WITH
PHASE A 3-500KCMIL 4" EMT
PHASE B 3-500KCMIL 4" EMT
PHASE C 3-500KCMIL 4" EMT

 

[Dennis Alwon]

No you cannot have all of one phase in one conduit. There is an exception but it is with pvc conduit underground -- I believe

(1) Paralleled Installations. Conductors shall be permitted
to be run in parallel in accordance with the provisions of
310.10(H). The requirement to run all circuit conductors
within the same raceway, auxiliary gutter, cable tray, trench,
cable, or cord shall apply separately to each portion of the
paralleled installation, and the equipment grounding conductors
shall comply with the provisions of 250.122. Parallel runs
in cable tray shall comply with the provisions of 392.20(C).
Exception: Conductors installed in nonmetallic raceways
run underground shall be permitted to be arranged as isolated
phase installations. The raceways shall be installed in
close proximity, and the conductors shall comply with the
provisions of 300.20(B).

 

[augie47]

I might add that even if you do use PVC conduit, you have to make provisions in the event the conduits terminate in a metal enclosure.
In the event these are service conductors it would be a good idea to check with your POCO as some of them prohibit such installations.

 

[kwired]

There is a fairly recent thread where the OP had encountered just what you described - IIRC same raceway and conductor sizes even.

He had some heating issues at that install.

 

[milemaker13]

No. Each conduit must have opposing phases in order to avoid magnetic heating of the pipe. Each conduit needs to have all 3 phases.

 

[iwire]

Here is a example of applying the exception Dennis mentioned.

While fine in PVC underground it isa no go with EMT.

 

[Ponchik]

Why is it OK with PVC?

A) Is it because the PVC will minimize the heat transfer and other combustable material touching the conduit will not be a fire hazard?

or

B) The magnetic heating is not an issue because the conduit is not metal?

 

[augie47]

B

 

[Dennis Alwon]

B

You talk too much Gus... I hate long winded replies...:lol:

 

[augie47]

On longer posts I make more errors.. on that one I had a 50-50 chance.

 

[kwired]

Why is it OK with PVC?

A) Is it because the PVC will minimize the heat transfer and other combustable material touching the conduit will not be a fire hazard?

or

B) The magnetic heating is not an issue because the conduit is not metal?

Not only is it not metal, it is not steel. Aluminum conduit possibly would have some problems but not as much as a steel conduit.

 

[Ponchik]

Thanks Augie and Kwired.

 

[jaggedben]

Would there be any point in taking advantage of the PVC exception? Is it somehow easier run all of one phase in a conduit? (I mean some advantage besides having people who don't quite know what they are doing be able to 'get away with' a code compliant install).

 

[roger]

Would there be any point in taking advantage of the PVC exception? Is it somehow easier run all of one phase in a conduit? (I mean some advantage besides having people who don't quite know what they are doing be able to 'get away with' a code compliant install).

Typically it makes it easier to keep the paralleled conductors close to the same length and it makes it much easier to terminate.

Roger

 

[roger]

MAY I RUN 3-500KCMIL FOR ONE PHASE EXAMPLE:
3-4" EMT IN PARALELL WITH
PHASE A 3-500KCMIL 4" EMT
PHASE B 3-500KCMIL 4" EMT
PHASE C 3-500KCMIL 4" EMT

Does the term "inductive heating" ring a bell?

Roger

 

[GoldDigger]

Does the term "inductive heating" ring a bell?

Roger

No, but it makes the bell too hot to hold.

 

[GoldDigger]

Would there be any point in taking advantage of the PVC exception? Is it somehow easier run all of one phase in a conduit? (I mean some advantage besides having people who don't quite know what they are doing be able to 'get away with' a code compliant install).

FWIW, for an existing duct bank, it allows you to avoid the need for all of the parallel raceways to be the same size.