Grounding Conductor to Automated People Mover 1

[jerebear]

In a transportation tunnel we are building we have installed a grounding grid under the concrete slab. Prior to pouring the concrete a waterproofing membrane was applied on top of the sub soil. The grounding conductor is stubbed up through the waterproofing membrane to be attached to the rail for the people mover. The waterproofing contractor wants to unbraid this 4/0 ground conductor to inject "Bituthene Deck Prep" between the conductors. We would then need to twist all of the individual conductors of the 4/0 cable togther for attachment to the rail.
Does anyone have any idea what affect this might have on the conductor. Is it a bad idea/

 

[IRstuff]

What sort of effect did you think there might be?

TTFN

FAQ731-376

 

[dpc]

Seems like a bad idea to me, at least from a Code compliance perspective. There is no way this will permanently prevent moisture from wicking up the conductor, if that is the concern. It's generally not a big problem anyway.

But I would be concerned about how this junk might effect the terminations and also how it would behave on that fateful day when 30,000 A goes through one of those ground conductors.

Put yourself in the position of the electrical inspector - would you sign off on that installation?

David Castor

http://www.cvoes.com

 

[jerebear]

If I was the electrical inspector I wouldn't pass it, that is one of my concerns. The cable has been modified from it's original form even though all the strands may be there.
Just seems like an all round bad idea. Part of my issue is I have a design team telling me this is what needs to be done to waterproof the cable. I agree this won't help much but the waterproofing installer is saying that unless we do this his warranty is void. Kind of a Catch 22 situation.

 

[dpc]

And his warranty covers electrocutions?

You're stuck in the middle, but I would not let some mud daubers dictate the electrical safety design.

You could request a variance from the local AHJ - then they can be the bad guys when they turn it down. It probably won't bother them a bit, and it gets you out of the middle.

If the AHJ accepts it (in writing), then all you can do is document your concerns and move on to the next problem.

David Castor

http://www.cvoes.com

 

[IRstuff]

I imagine that these conductors are machine-wound, under some amount of tension and stress. Unwinding/rewinding potentially introduces additional stress. I

t's unlikely that you'll be able to rewind it to the same pristine condition that the original machine winder produced, so there's a possibility that the overall resistance structure is changed. Moreover, there's a great likelihood that all this handling will increase the inter-strand resistance through dirt and oils, without even worrying about the goop contaminating things.

TTFN

FAQ731-376

 

[waross]

Question; How does the contractor propose to unwind the strands that are cast in the concrete?
Suggest the contractor use a sealing substance with flow characteristics that will allow it to penetrate between the strands.
Option two: Break out the concrete and cast a Cad-Weld splice on each conductor. Alternately use a compression barrel that will compress the strands into a solid form. Re-pour the concrete. That will seal the conductors.
Option three; Slide some sort of compression collar down the cables to about two or three inches from the concrete. Compress well. Give this about a quarter turn with a pipe wrench to open the strands. Let the sealer have at it. Have the AHJ sign off on this method first.
Strongly suggest that the cables should have been sealed some way prior to the concrete being poured and any expense will be to the account of the sealing contractor..

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

I like Bill's suggestion for a Cadweld fitting. That would likely provide a good seal that would not cause the inspector any heartburn.



David Castor

http://www.cvoes.com

 

[hdp]

Solder block?

 

[jerebear]

Thanks for all the suggestions, I will have some conversation with the AHJ and the owner for acceptance and see where it goes.