RMC - aluminum type

Grouch

Grouch

Senior Member
Location
New York, NY
In NYC, aluminum RMC is not permitted to be encased in concrete, per the NYC amendments (section 344.10).

If the conduit punches through a slab, to go from one floor to the next, is that considered 'encased in concrete' in that one area?

I assume the answer is no, since the conduit will be surrounded by fire-stopping material. 'Encased in concrete' would have the conduit buried in concrete.
 
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If the RMC is a installed before the concrete is poured then it is encased in concrete. If it's just going through a hole in the concrete it is not encased. Typically aluminum RMC goes through a sleeve when running from floor to floor.
 
It never was allowed to be encased in concrete per the NEC because it constitutes a corrosive environment. The NYC amendment just makes that clear to anybody who might not know that aluminum and concrete don't play nice especially if there is any moisture.

As to being run through a concrete slab, I don't think I would rely on the fire-stopping material to isolate the conduit from the hole walls. There probably is an epoxy or other coating that you can apply to the section of conduit that is in the hole before you firestop.

Grouch said:
If the conduit punches through a slab, to go from one floor to the next, is that considered 'encased in concrete' in that one area?
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Dunno. You should ask the AHJ.

-Hal
 
infinity said:
Aluminum can touch concrete.
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In my experience, not a good idea. Any moisture and you will have a hole in the conduit. I ran aluminum through a boring in the soil UNDER a sheltered concrete patio. I came back years later to add another conductor and all that was left was toothpaste. Either side of the patio, the conduit was fine. Apparently, whenever it got wet, alkali leached out of the concrete, down into the soil below and rotted the aluminum.

So, while the NEC only prohibits encasing aluminum conduit in concrete, I take it a step further and don't run it on untreated concrete or through without protection. The NEC also prohibits direct burial, but surprisingly any that I have seen (at least in this area) has suffered no deterioration at all after many years.

-Hal
 
hbiss said:
The NEC also prohibits direct burial, but surprisingly any that I have seen (at least in this area) has suffered no deterioration at all after many years.
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Haven't done it myself, but have seen several cases of aluminum RMC used as a sleeve from an enclosure to below grade for direct burial cables, no extreme deterioration on any of those either.
 
electrofelon said:
Sometimes I think we go a little overboard with assuming concrete is always wet. Yes I understand concrete is hydrophilic, but from the description this not below grade or anything, it should be bone dry.
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Yup which is why there is not an issue running aluminum conduit through a hole in dry concrete. There is quite a bit of general overboard when it comes to aluminum conduit. You always hear about the dissimilar metals non-issues. After all aluminum raceways use steel locknuts and enter steel boxes and panels without any problems.
 
infinity said:
Yup which is why there is not an issue running aluminum conduit through a hole in dry concrete. There is quite a bit of general overboard when it comes to aluminum conduit. You always hear about the dissimilar metals non-issues. After all aluminum raceways use steel locknuts and enter steel boxes and panels without any problems.
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We also have cast aluminum conduit bodies and such, and I do run into aluminum cabinets at times where we enter with steel raceways/fittings. Not so much general purpose cabinets but definite purpose cabinets containing controls and made by the manufacturer of the equipment it supplements.
 
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