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-   -   Vertical EMT run - Max length and cable support? (http://www.diychatroom.com/f18/vertical-emt-run-max-length-cable-support-29477/)

ScottR 10-06-2008 01:09 PM

Vertical EMT run - Max length and cable support?
 
Hi All,

First time poster/frequent reader.

I just bought my first house, and I'm anxious to get started on a bunch of projects, one of which is to install recessed cans throughout my second floor (in 4 rooms). I'd like to home run each room on its own circuit, mostly for future home automation purposes (not a fan of X10 and its ilk, and I'd prefer not to have remote wired dimmers throughout the house).

My ideal is to have a few runs of EMT from the basement up through both levels to the attic. I'm clear on derating, free space, etc in conduit (mostly). What I'm not sure about is the weight of the cable. I would have a vertical drop within the conduit of about 20 ft (second floor is an addition and so there is a rediculous amount of space between the first-floor ceiling and the second-floor floor).

I don't like the idea of the conductors supporting their own weight for that distance. So how are wires usually supported in this situation? I'd imagine that it comes up frequently in commercial work.

I've done plenty of NM and AC wiring, but haven't used conduit aside from a couple of outdoor lights. And just to head off the "use romex" answer: I'm running this conduit to make future pulls from basement to 2nd floor easy. (I like to reconfigure). And I'm doing multiple conduits to keep electric and data seperate. :)

Thanks in advance,
Scott

InPhase277 10-06-2008 01:43 PM

For the size of conductors you are likely to use, no support is required for vertical runs until you reach 100 ft. But if you are just interested, there are support bushings available that go over the opening of the pipe. The wires pass through and the shape of the bushing is like a wedge, so the weight of the wires tightens the bushing around them.

What's important is bonding the conduit properly at both ends.

ScottR 10-06-2008 01:50 PM

Thanks, that makes me feel better about my measly 20ft. Just curious, at what point does the gauge get too heavy for a 100ft drop (well, or can you point me to the relevant part of the NEC?)

For my own anal retentive purposes, I'm probably going to run a large ground up through the conduit anyway, and will bond to the box at the top -- the bottom will connect with the service panel anyways. Also will ground both ends of the comm conduits with that wire.

InPhase277 10-06-2008 01:58 PM

Quote:

Originally Posted by ScottR (Post 168973)
Thanks, that makes me feel better about my measly 20ft. Just curious, at what point does the gauge get too heavy for a 100ft drop (well, or can you point me to the relevant part of the NEC?)

For my own anal retentive purposes, I'm probably going to run a large ground up through the conduit anyway, and will bond to the box at the top -- the bottom will connect with the service panel anyways. Also will ground both ends of the comm conduits with that wire.

The NEC section is 300.19(A), and for copper, above 1/0, support is required at 80 ft and less from there.


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