Parallel ?

[Rockyd]

Ed CarrI have two 4" rigid conduits each containing six
500mcm cu conductors. They are feeding a 3 phase
panel with a neutral. My inspector is telling me
that it may not pass. In conduit #1 I have phase A and phase B.
In conduit #2 phase C and the grounded conductor.
I have been going through my book and can't find anything
that says this is a violation. This is the service entrance
from utility transformer. Anyone?

Thanks, Ed

Hate to be the bearer of bad news, but let me give you the information as I see it.

Check 300.5(I) ex 2

Then check 300.20(B)

The installation you describe has a picture of said example in Mike Holt's "101 Essential NEC Rules" (page 128)

There are four raceways entering the bottom of the equipment. A phase in the first, B in the second, C in the third, and the N in the fourth, in what appears to be PVC.

Doesn't look good for what you are suggesting.

 

[jumper]

Here is a picture of what RockyD is describing, it is called isolated phase:

View attachment 4586

 

[dbuckley]

Not only is this a violation, if that rigid conduit has continutiy between conduits at each end, its downright dangerous, due to the induictive effects mentioned by Roger above, which will cause heating, and under the right circumstances, the story may end catastrophically.

 

[Rockyd]

Thanks Jumper, that's exactly what we're talking about.

 

[jumper]

Thanks Jumper, that's exactly what we're talking about.

No problem, I swiped the pic from Iwire.:grin:

 

[benaround]

Ed,

What is the load that needs to be served ? If the existing service was compliant, you

would have 3 x 380 x .8 = 912amps and if you installed a,b,c,&n in each pipe you would

have 760amps, that is only a difference of 152amps. Compare 8 conductors to 12 conductors

and only a gain of 152 amps ?

 

[Ed Carr]

Thanks to everyone that responded to my question.
I am going to add a 3rd 4" rigid and put 4 wires in
each. So then brown,orange,yellow & neutral in each
correct? The picture that jumper posted would be allowed
if the conduits were nonmettalic?

Ed

 

[augie47]

Thanks to everyone that responded to my question.
I am going to add a 3rd 4" rigid and put 4 wires in
each. So then brown,orange,yellow & neutral in each
correct?

Yes

The picture that jumper posted would be allowed
if the conduits were nonmettalic?

By NEC yes, by some POCOs, no

Ed