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MC cable in a damp location #209645 04/15/13 07:58 AM
Joined: Jan 2004
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George Little Offline OP
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Do we have any information that makes it clear about running MC cable in a damp location. I can find wet locations and dry but nothing on a damp location?


George Little
2017 / 2014 NEC & Related Books and Study Guides
Re: MC cable in a damp location [Re: George Little] #209646 04/15/13 09:52 AM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline
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George:
No, I can't see anything that is clear on this.
IMHO, the sheath materials should be clarified,between the steel and aluminum.

I have seen the aluminum sheath deteriorate in a few installs from condensation.



John
Re: MC cable in a damp location [Re: George Little] #209651 04/15/13 01:33 PM
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Posts: 9,568
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gfretwell Offline
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What is the question? If the MC is wet location rated, doesn't that encompass damp locations?

I looked at the MFG page for the Southwire MC-XHHW (one of the wet location MCs), it says that is an XHHW-2 conductor and that conductor is listed wet and damp (330.10(A)11(c)). I assume you would derate from the 75c column in a damp location like you do in a wet one.


Greg Fretwell
Re: MC cable in a damp location [Re: George Little] #209652 04/15/13 02:27 PM
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Tesla Offline
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Greg...

My Ugly's has XHHW-2 as a 90c conductor for derating purposes.

Even XHHW is rated 90c.



Tesla
Re: MC cable in a damp location [Re: George Little] #209655 04/15/13 04:46 PM
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gfretwell Offline
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I guess I "assumed" wrong wink

The box of EZ-MC I have says you derate at 75c when wet but that is not exactly the same stuff. Southwire did not even reference that on their page. Maybe it was a THHN/THWN product that was replaced by the XHHW


Greg Fretwell
Re: MC cable in a damp location [Re: George Little] #209701 04/18/13 10:17 PM
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mikethebull Offline
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330.10 (A)(11) gives conditions for MC in wet locations.

Re: MC cable in a damp location [Re: George Little] #209704 04/18/13 10:24 PM
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Tesla Offline
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Greg...

That XHHW-2 stuff is creeping in all over the place.

I first saw it with aluminum feeders. Now, it's popping up around stranded copper, from time to time.



Tesla
Re: MC cable in a damp location [Re: George Little] #209708 04/19/13 02:41 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline
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George:
Are you refering to the sheath, or the conductor insulation?



John
Re: MC cable in a damp location [Re: George Little] #209709 04/19/13 03:23 PM
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gfretwell Offline
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The aluminum armor is considered suitable for wet locations if the wrapper and conductors are wet rated. I understand that salt air can eat it but when you are talking about the sea shore, galvanized rigid metal is not that great either.


Greg Fretwell
Re: MC cable in a damp location [Re: George Little] #209710 04/19/13 06:11 PM
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Tesla Offline
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Greg...

Carrying that thought further, any aluminum bussing installed near the ocean is at hazard for AlCl3 'rust.'

Aluminum is normally considered 'rust proof' because run-away corrosion does not occur -- unless chloride ions are present.

But, aluminum is, in fact, prone to ultra-rapid 'rusting' / oxidation. Bare aluminum metal oxidizes promptly in air. It acquires a THIN coat of Al2O3 -- aka alumina. It's so thin that you can see right through it. Unlike iron oxide rust, alumina expands to lock up tight, creating an air tight seal.

If salt air is misting in, the chlorine displaces the oxygen in the alumina. Now the metal loses its sheild. AlCl3 shrinks like common rust. Given enough time, aluminum metal becomes pitted -- with cruddy AlCl3 ( it's yellow ) crystals at the surface.

I've witnessed bussing that's picked up a 3 volt drop right at the rails (under load) over a twenty-year period.

The solution is to kill power, buff the crud off the rails, clean the breaker-rail contacts and re-assemble.

Where it's an issue, copper bussing is worth the premium. Copper does not rapidly react with salt air like aluminum.

This issue is why aluminum can't be totally trusted below grade. Some American soils are absolutely laden with old ocean salts. (Nevada, California, Utah, Arizona,...) So you can't trust aluminum to stay bonded as part of a GEC system.



Tesla
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