Parallel 350 MCM Entrance Conductors?

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Physis 2

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I was looking at a building that's near completion recently and I see that there are two sets of 350 MCM both emerging from their own weather heads and landing on the same busses in the panel. 4" rigid, each with an LB to get into the building.

First (without looking it up) the bend radius I'm pretty sure is too tight. One of the LB's is open and I'm thinking it might be because the inspector isn't accepting it.

I don't do this size services and was only looking at it because it seemed weird to me. I, not being obsessed or anything, ( :D ), asked another electrician, a friend of mine, who was already there anyway for something else, what he thought of it.

He's thinking that the entrance conductors were paralleled to reduce the required bend radius of 750 MCM so they could use the LB's.

I don't buy it because I think it could have been done with a mast to begin with and there wouldn't have been a radius issue.

Any other thoughts on why the parallel conductors?
 
Re: Parallel 350 MCM Entrance Conductors?

1) Cost.


2) Availability (or lack thereof) of 750.

3) Bending 750 is a nightmare, terminating is a nightmare (i've never done it, I just know anecodotally)
 
Re: Parallel 350 MCM Entrance Conductors?

Originally posted by peter d:
1) Cost.


2) Availability (or lack thereof) of 750.

3) Bending 750 is a nightmare, terminating is a nightmare (i've never done it, I just know anecodotally)
Click to expand...
actually, I would rather bend cables above 500, than any below. It seems to me, 500s and below are less ply able than above 500. I think it is a result of the number of strands vs. the circular mills of each strand.

As far as the bending radius issue, yes some LBs can be really tight. I think a 4" LB with 4-350s is not in violation. When I use LBs, I order the mogul (longer opening) LBs, and the cables just "fall" into the LB.
:)

Gerry
 
Re: Parallel 350 MCM Entrance Conductors?

I don't recall the exact point, but over a certain size, LB's specify their capacity by maximum quantity of a certain size of conductor, rather than going by the size of the conduit attached.
 
Re: Parallel 350 MCM Entrance Conductors?

I don't recall the exact point, but over a certain size, LB's specify their capacity by maximum quantity of a certain size of conductor, rather than going by the size of the conduit attached.
Click to expand...
If the maximum number of conductors is not marked on the LB, then you have to apply the rule in 314.28(A)(2).
Don
 
Re: Parallel 350 MCM Entrance Conductors?

IMHO, you have brought up something that I feel is too often overlooked by many inspectors.
Very often, standard condulet fittings, like LB's are not rated for the same number of conductors as the associated size conduit and I have often witnessed wire damage when this was not taken into consideration, especially on larger conductors. I brought this up in 1 jurisdiction and the answer by the AHJ was "well, no supply house stocked the "mogul" LB's"...duh! maybe cauae we didn't enforce it ??
As Gerry mentioned, the mogul LBs are a plus. One mfg, Appleton I believe, makes an LB with NEC in the catalog number. One entire half of the fitting unbolts,,its great ..with 500 MCM its kinda like throwing dead cat thru an open sklight... wish more folks would use them.
 
Re: Parallel 350 MCM Entrance Conductors?

Originally posted by augie47:
. . . its kinda like throwing dead cat thru an open sklight . . .
Click to expand...
Now, there's an analogy you don't hear every day! ;)
 
Re: Parallel 350 MCM Entrance Conductors?

Take a look at the exception to 314.28(A)(2).

I see 5 inches as the answer?

Does this mean that a 4 inch LB is too small?
I was always under the assumption that a 4 inch LB would be fine for this type of installation????
 
Re: Parallel 350 MCM Entrance Conductors?

Originally posted by augie47:
..with 500 MCM its kinda like throwing dead cat thru an open sklight...
Click to expand...
That's great! :D Never heard that one before, gotta write that down and use it. Too funny!!!!!
 
Re: Parallel 350 MCM Entrance Conductors?

Pierre,
I see 5 inches as the answer?
Does this mean that a 4 inch LB is too small?
I was always under the assumption that a 4 inch LB would be fine for this type of installation????
Click to expand...
If the distance between the inside wall of the LB and its cover is less than 5" it is too small for use with 350kcmil conductors unless the fitting is marked per 314.28(A)(3).
Look here for a conduit body fill chart from one manufacturer.
Don
 
Re: Parallel 350 MCM Entrance Conductors?

Frank,

I should have also mentioned that it's single phase, so only three wires. And I don't think conduit size was an issue, they could have used whatever they needed to.

And yes, Sam :D

Throwing cats, dead or alive, through skylights? Does that mean it's easy? :D

Larry,

I was told the same thing about the conductor markings, I don't use stuff that big though so I don't know.

I still don't feel like anyone's come up with a decent justification (myself included) for why they ran this parallel.

Edit: Peter, I think the two sets of conduit would more than cancel any conductor savings.

[ October 17, 2005, 04:55 PM: Message edited by: Physis 2 ]
 
Re: Parallel 350 MCM Entrance Conductors?

Originally posted by Physis 2:
Edit: Peter, I think the two sets of conduit would more than cancel any conductor savings.
Click to expand...
I never deal with wire that size, so I must admit to being an educated guess on my part. I know that one of the main reasons for parallel installations is to reduce cost. Without knowing all the finer details, I'm sure the installers must have weighed all the options prior to installation. But then again, maybe they didn't. :confused:
 
Re: Parallel 350 MCM Entrance Conductors?

Sam
you mentioned 750 (I assume one set) vs. 350 (two sets)
The two are not equal in ampacity, so I would need more info to take a guess.
one 750 = 475 amps
two 350's = 620 amps

What is the service OCPD rated?

Dead cat through a skylight = priceless analogy
I'll file that under "things to use to break up the tension" thanks
I suppose you could use dead poodle or other hated animal of your choice!
 
Re: Parallel 350 MCM Entrance Conductors?

I see 5 inches as the answer?
Does this mean that a 4 inch LB is too small?
I was always under the assumption that a 4 inch LB would be fine for this type of installation????
Click to expand...
Also in addition to Dons answer, you're still required to have the conduits six times the conduit trade size apart.
 
Re: Parallel 350 MCM Entrance Conductors?

I'd ask these guys but I don't speak Chinese. :D

That's an interesting point about ampacity Larry, I'm like Peter, I don't use a lot of bigger stuff like this, I hadn't considered the unequal ampacity versus size with larger conductors.
 
Re: Parallel 350 MCM Entrance Conductors?

And I looked at it last night, it's 600 amp.

You should be an inspector Larry! :D
 
Re: Parallel 350 MCM Entrance Conductors?

Originally posted by Physis 2:
And I looked at it last night, it's 600 amp.

You should be an inspector Larry! :D
Click to expand...
What are you doing sneaking around in the dark????

Maybe you should be the inspector!!!! ;)
 
Re: Parallel 350 MCM Entrance Conductors?

Stop trying to recruit me Larry. :D

It's a building that's going up next to an adult beverage facitility a friend of mine owns. He thinks I look like an inspector too. :D
 
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