Panel Disconnect Wiring

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tganz96

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Dallas , Texas
We have a panel that one of our contractors built and we have not installed it yet.

The panel has a smaller panel mounted to the right hand side that is housing the 400 amp disconnect and they made 3 holes and installed 1 inch cord connectors (1 for each phase)to pass the power into the distribution block of the control panel.

The cord connectors are about a half inch apart. One of our older electricians said we needed to change this as the phases being seperated like that and running though 3 different cord connectors would produce eddy currents and heat up in that area? Is this true? How big of a problem is it?

Our electrician suggesed changing it to use 1 large cord connector for all 3 phases. Each phase is DLO cable coming from the lod size of the disconnect.
 
iwire said:
It could cause heating and it is an NEC violation.

See 300.20(B).
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Yes, and it sounds as though they were perhaps trying to work around some arc flash issues, I've been seeing things like this a lot lately. Some of the enclosure mfrs are now selling enclosures that have a separate section for just the main disconnect so that they are not in the same air space as the rest of the panel. That way a user can enter the panel with minimal PPE, which can be problematic if the line disconnect is sharing the same space since the line terminals are still hot. What happens though is that some panel builders think they can create the same thing by just slapping a disconnect switch on the side of the box, not understanding the inductive heating issue of separating the 3 phases. In the factory built versions, I believe they use a non-conductive gland plate for the sealed pass-through. In this version, you would have to use a single cord grip that allows all three in one hole, which might not exist, or separate them by a greater distance (not sure of that though, don't have my NEC here but we used to do that a long time ago, it was something like 12" I think? Maybe someone else can confirm or comment.).

And HOPEFULLY everyone understood the complexities of terminating DLO cable, which might be another can of worms. I see a lot of inexperienced panel builders use that without investigating the fact that most mechanical lugs are NOT rated for anything other than class B stranding, which does not include DLO.
 
Jraef said:
And HOPEFULLY everyone understood the complexities of terminating DLO cable, which might be another can of worms. I see a lot of inexperienced panel builders use that without investigating the fact that most mechanical lugs are NOT rated for anything other than class B stranding, which does not include DLO.
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They just know it is a lot easier to bend.
This is where quality control should step in and point out the above.
If they know it.
 
Is it possible to cut a slot between the three holes, so as to make "one" hole from an inductive point of view?

Something like this:

O-O-O


Termination of DLO cable is another story entirely. When I've had to land DLO and type-W, my AHJ has always been satisfied with me using ferrules under standard lugs. My AHJ is the practical type though. YMMV



SceneryDriver
 
SceneryDriver said:
Termination of DLO cable is another story entirely. When I've had to land DLO and type-W, my AHJ has always been satisfied with me using ferrules under standard lugs. My AHJ is the practical type though. YMMV
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There are listed connectors available for flexible cable in both compression and mechanical style. This should no longer be much of a problem other than having the right connector.
 
petersonra said:
There are listed connectors available for flexible cable in both compression and mechanical style. This should no longer be much of a problem other than having the right connector.
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This is absolutely true and I use rated lugs where applicable. There have been times, however, when I've had to land high-flex wire on devices such as contactors, and the use of ferrules satisfied my AHJ.

I build control cabinets for special effects and stage automation, and some of the things we end up having to do - custom fabricated enclosures to fit strange locations, for instance - have always amused our inspector. We have a good working relationship; we don't try to hide anything from her, and she's willing to answer questions before they become issues.

Last year, I had to bring up a 4' sq. propane fueled "camp fire" through a hole in the floor of the stage, with actors all around, in a 600 seat house, in an indoor theater. That's one of the less weird things I've done lately too.

I have a silly job ;)


SceneryDriver
 
SceneryDriver said:
This is absolutely true and I use rated lugs where applicable. There have been times, however, when I've had to land high-flex wire on devices such as contactors, and the use of ferrules satisfied my AHJ.
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What are ferrules? I know what they are on a plumbing connection, but I'm not familiar with the term electrically related.
 
In this case it would be a thin compressible copper tube that fills in the space around the thin strands. Or a similar copper sheet rolled around the wire before inserting into the connector and crimping.


Tapatalk!
 
GoldDigger said:
In this case it would be a thin compressible copper tube that fills in the space around the thin strands. Or a similar copper sheet rolled around the wire before inserting into the connector and crimping.


Tapatalk!
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I have used copper sheet shim stock like that before. Just never heard or seen electric ferrules.

Would it be acceptable to strip 2x (double) the amount of insulation and folding the strands back, thereby doubling the contact area of the strands?

I may or may not know someone who has done that!
whistling2.gif
 
Little Bill said:
I have used copper sheet shim stock like that before. Just never heard or seen electric ferrules.

Would it be acceptable to strip 2x (double) the amount of insulation and folding the strands back, thereby doubling the contact area of the strands?

I may or may not know someone who has done that!
whistling2.gif
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A lug with a set screw in direct contact with the fine strands can damage strands even break some strands off - just one reason that style is generally not rated for use with fine stranded conductors. If it has a pressure plate on the end of the set screw or other design here that turning screw is not in direct contact with the conductor it is likely listed for fine strands.

Doubling the contact area like you mentioned is a compromise that likely does have some benefit - but is not an NEC recognized way to deal with the problem, and very likely not recognized by listing standards either.
 
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