Conduit in Basement question.


Old 09-29-09, 06:58 AM
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Conduit in Basement question.

I had posted earlier regarding running boards vs. conduit to run perpendicular to the basement joists. I have decided to go with conduit mainly because it gives me a cleaner look and allows me to relocate some of the lines.

I will be using 3/4 EMT going into metal J-boxes. Probably going to use 2 runs with one being 15 feet and the other maybe 25 feet. The wire will transition from 12-2nm to 12 gauge THHN in the box and through the conduit.

I would like to attach the junction boxes to the underside of the joists with an offset to one side of the joist to allow the spliced wire (12/2nm) at the end of the conduit run to run up into the joist space again.


--Is this acceptable or does the box have to be mounted flush with the underside of the joist?

--If the box can be mounted to the underside of the joist is it allowed to offset to one side rather than the joist running down the center of the box?

--I will be running 2 circuits through each 3/4 EMT. I am assuming the EMT size is overkill but it's future proof a little. Running 2ea red and white wires with a shared ground (1 12g wire) or separate grounds?

One circuit is 20a at the breaker, the rest are 15 I believe. I am assuming derating does not apply with the runs described above?

Any tips, pointers or general advice beyond what I have mentioned above before I head out to the local HD to but this stuff would be appreciated.
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Old 09-29-09, 07:42 AM
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Traditionally the conduit would be bent at each JBox to compensate but you can also use offset couplings.
Old 09-29-09, 07:47 AM
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The EMT and Conduit will both be attached to the bottom of the joist. I will probably use an offset coupling to attach them rather than try to get bending down to a science.
Old 09-29-09, 09:23 AM
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You could also just come out of the back of the box. You would mount the JB on the vertical face of the joist.
Old 09-29-09, 09:33 AM
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I think I am confusing myself here

This is how I was thinking of installing the junction box and conduit flush with the bottom side of the floor joists. There should be no offset.

The transition from THHN and NM would be in the box with the NM running out the top (back) of the box up into the joist spaces similar to the two black cables in the upper right hand part of the picture.

This isn't my picture BTW but it's the only one I can find to show what I am trying to describe. The junction boxes at either end wont interconnect with another JB. They are just a means to transition from the joist spaces (NM) to the conduit (THHN)

Last edited by ragifiro; 09-29-09 at 09:34 AM. Reason: Attributed picture to owner's blog (not me)
Old 09-30-09, 06:21 PM
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Nothing wrong with this. You probably don't even have to use offsets actually.

If there's any chance of ever finishing the ceiling, I'd suggest keeping as much of the conduit either along the exterior walls (or main supporting beams), or up inside the joist bays. It also keeps everything neater overall.

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