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#209645 04/15/13 08:58 AM
Joined: Jan 2004
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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
Joined: Apr 2002
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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
Joined: Jul 2004
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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
Joined: Jun 2004
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Greg...

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

Even XHHW is rated 90c.



Tesla
Joined: Jul 2004
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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
Joined: Mar 2007
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330.10 (A)(11) gives conditions for MC in wet locations.

Joined: Jun 2004
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T
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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
Joined: Apr 2002
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George:
Are you refering to the sheath, or the conductor insulation?



John
Joined: Jul 2004
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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
Joined: Jun 2004
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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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