Conduit wiring method

[DaveNay]

I am adding a small (240V/30A) subpanel to a building adjacent to my workshop. A short length of the feeder will be underground through 1 1/2" PVC. Inside the buildings, I would like to stick with stapling the cable to the studs (for simplicity/cost/time). My question is, how do I make the transition from conduit to plane cable? Does the pipe just end with the wires coming out? Should I put some sort of a junction box with cable clamp (even though I would just run the cable straight through the box) ? I plan on using #8/3 UF cable.

Thanks,
Dave

 

[_RaT_]

I am not sure how code would treat running straight out of the conduit although I would not see an issue other then mice etc., getting in it to trim their teeth on your wire. I typically pipe right to the panel but in your case, you could always get a small junction box (6X6) with concentric knock outs that go up to 1 1/2" or larger and use a male adapter/lock ring to tie to the box. Problem is, you now need to ground that box so you would be forced to cut the #8 UF w/ground and ground the box. My preference would be to simply run it out of the PVC conduit ensuring no sharp edges are there to cut the very tough UF jacket. Perhaps the inspector has a thought on making this transition.

 

[beenthere]

I'd just put a regular thimble (cap with a hole in it) at the end of the conduit and keep the cables intact all the way to the box. The thimble protects the cable from any sharp edges on the conduit.

(My monitor must be teetering on the edge, as I cannot make out the diagram you provided. Many pics show up dark, and the 'bright' adjustment is at its limit)

 

[DaveNay]

I modified the image for you. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Just putting a protective cap (thimble?) on the end of the conduit, or just a good deburring would definitely be my prefered method.

Dave

 

[beenthere]

Thanks for the image. What you show is what I did when I ran electric lines to my shed. If I remember correctly, I only used the conduit sweeps at each end to hold the underground cable burried in the trench. I add a wad of silicone seal also to plug the space and hold the wires centered in the conduit. Probably not necessary. As long as the wires are not connected outside a box, it should be okay.

 

[Jim_Slagle]

put a pvc straight (or 90 degree) lb box on the end of the conduit, glue a female threaded adaptor into the other end of the lb, and get a 1 1/2" cord grip of the correct size for the cable.

 

[neilly2]

I believe the controlling factor is the susceptability to physical damage (relative to the exposed wire). For example exposed wire could not be within 6' of the ground level in case of being hit by something. On a parking garage project, we were required to run rigid steel conduit to above 6' then could transition to PVC. (a car wouldn't be hitting it above 6')

Also notice that residential service wire fed from above is usually exposed, but fed from underground is in conduit.

The other controlling factor is that the insulation is rated for an exposed area.

The transition of conduit to exposed is fairly common. You don't need any special transition. If the edge of the conduit can cut through the insulation than the installation is poor.

Look at an underground feeder coming down from a utility pole. The wire is run down the pole and covered with a metal molding, then the wire runs into the conduit sweep. The conduit is then gooped up around the wire.

Local code guy will have the info.

 

[DaveNay]

A follow-up question.

I stopped by Home Depot last night to check on the cable, and both #8/3 NM-B and UF-B are the same exact price ($1.29/ft). Since I am planning to put this in conduit where underground, is the NM-B cable allowed to be exposed when inside the buildings? The NM-B would be much easier to work with than the flat UF-B, and also allow me to use a smaller conduit size.

Also.... why is the UF cable flat??? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

Dave

 

[Inspector507]

NM cable is not permitted to be used in conduit running underground. Whatever cable/conductor you use needs to be approved for a wet location.

 

[_RaT_]

We are not allowed to have romex or UF exposed. Your code may vary. UF is a pain to work with. I've only seen UF (underground feeder) come flat.