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Old 06-11-2019, 04:18 PM   #1
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Attic to crawlspace conduit: EMT or LFMC?


Hi guys,

I'd like to run empty conduit from attic to crawlspace while I still have a couple walls open. I'm not sure how exactly it will be terminated in the attic or crawlspace (no immediate use) but want the raceway to be there so I can close things up.

The minimum I need to do is about 10 feet vertically (8-foot walls with some extra top and bottom) with some slight offsets to negotiate the top and bottom plates.

I've got some EMT sticks and a bender and also got some LFMC (liquidtight aluminum flex) which seemed like it could be easier to deal with at the termination points and would save me time making the (relatively simple) offset bends.

NEC Article 348 and 350 says that FMC/LFMC require the same nail protection as Romex. It's going to be hard to maintain the required 1-1/4" clearance with such a large outside diameter. +1 for EMT.

Does the corrugated interior make pulling wire difficult? Any other considerations besides cost?

Thanks!

Last edited by ablodneyget; 06-11-2019 at 04:32 PM.
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Old 06-11-2019, 04:36 PM   #2
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Re: Attic to crawlspace conduit: EMT or LFMC?


Quote:
Originally Posted by ablodneyget View Post
Hi guys,

I'd like to run empty conduit from attic to crawlspace to enable future telecom, alarm system, or new circuit pulls without cutting open finished walls. I have one last wall open that is a great candidate for conduit. I'm not sure how exactly it will be terminated in the attic or crawlspace (no immediate use) but need to get a raceway in there so I can button the walls up.

The minimum I need to do is about 10 feet vertically (8-foot walls with some extra top and bottom) with some slight offsets to negotiate the top and bottom plates. The crawlspace will probably need a compound 90-degree bend to terminate to a box, so I might want some flex down there anyway for the last few feet. Would prefer to avoid bending conduit down there.

I picked up some 5-foot sticks of EMT (10-footers are too long) and also got some LFMC (liquidtight aluminum flex metal conduit). The latter I've never used before, but the airtightness and flexibility are appealing, and I have a Rotosplit cutter for that size that I used on MC cable during my rewire. Obviously it's not the most cost-effective option. I have access to an EMT bender but wouldn't call myself a pro at bending it.

Does the corrugated interior make pulling wire difficult? Any other considerations besides cost? It does seem like silly overkill but could yield some installation time savings. Does the jacket on LFMC cause derating or durability concerns?

My interpretation of the NEC is that FMC does not provide the same level of protection as EMT and would need to be nail plated at the top and bottom since it is likely to end up within 1-1/4" of the drywall, whereas extra protection would not be needed with EMT.

Thanks!
I don't see a problem using the LFMC for the entire run. You would just need to terminate it into junction boxes to pass inspection. You cut LFMC with a straight perpendicular cut using a hacksaw. The Rotosplit will give you a rough edge. Nail plates are good idea for LFMC and EMT. LFMC has a PVC jacket. The only issue is when there is a fire from toxic smoke. The inside wall of LFMC is not as smooth as EMT, but it should not be a major concern. The non-metallic (LFNC) is a lot more difficult to pull through. Use wire pulling lube.
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Old 06-11-2019, 04:38 PM   #3
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Re: Attic to crawlspace conduit: EMT or LFMC?


Check out the cost of LFMC box connectors. They are costly. EMT is more economical as well as accommodating an easier pull.

Last edited by brric; 06-11-2019 at 04:41 PM.
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Old 06-12-2019, 08:21 AM   #4
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Re: Attic to crawlspace conduit: EMT or LFMC?


I would go EMT a bit more work now but you'll be happier later. You say it is accessible now so shouldn't be a huge burden. Also be aware of conduit fill vs ampacity derating. The latter can be the more constraining factor on what you can run in the conduit. If you are thinking just a feeder set for a future sub panel then no problem. If you are thinking 4 or more 15A branch circuits then the derating will become an issue.


If there are no wires installed today you can just leave the stubs open since it isn't considered electrical wiring yet (just some empty pipes in the wall) but a simple cap you toss away later wouldn't be a bad idea.
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