I've found bits and pieces that answer most of my project questions, but still a bit unclear. I have about 50' of UF-B and about 25' of NM-B, all 10/3. My project is to run a dedicated circuit from exterior panel (30amp 2-pole breaker w/interlock) from one side of the house to the other out to an exterior 30 amp power inlet box.

My plan is to run 1" PVC with UF-B from panel up through soffit and then exit cable after the 90deg turn into attic. From there i would run to a suitable location in the attic for a junction box where i would splice the NM-B. From there I would go to the other side of house and transition through another junction box back to UF-B. Pop through soffit again to exit attic and run 1" PVC conduit to outlet. There is no plan to use conduit through attic other than section that breaks the soffit plane. I would attach wire to rafter/studs as appropriate. Is this reasonable/meet code?

My second option, is to minimize junction boxes and go UF-B from panel to NM-B through attic in one junction box. From there, run remainder of distance with NM-B and come through garage ceiling and run inside of garage/block. Run some EMT for NM-B wire coming down and drill a hole through concrete, out to outlet box. Per my understanding I would need some type of conduit for NM-B through concrete? (which I'm still not clear if that puts NM-B into a "wet"-type of location...?) Attached is my interpretation of what this would look like. Appreciate any insight, corrections, and what the...?

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  • Sched 80 PVC can't fit 10/3 UF. You need pipe with an actual (not trade) inside diameter of more than 1.003". Take the wide dimension of the cable and multiply by 1.38, that's the ID you need. – Harper - Reinstate Monica Sep 20 '20 at 20:02
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    Or use THWN wires in conduit, not UF-B cable. – Ecnerwal Sep 20 '20 at 21:10
  • Is there a reason you want the UF in conduit, instead of simply strapped to the wall? – ThreePhaseEel Sep 20 '20 at 21:38
  • Does the .003" physically make it unsuitable or do i run the risk of electrically compromising something? These would be very short runs of conduit < 5 feet from the box to attic and < 7 feet from inlet box on other side. – carl12345 Sep 21 '20 at 3:02
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    @carl12345 Pipes have a "Trade Size" which is NOT the actual size. Here is a table of PVC trade sizes vs their actual ID. Sched 80 PVC is .957". Sched 40 is 1.049. The difference is the thicker wall. (the OD must remain the same because it must be able to go into fittings). jmeagle.com/sites/default/files/jme_Electrical%20Conduit.pdf – Harper - Reinstate Monica Sep 21 '20 at 5:39

Option 1 looks good. For my understanding you still need to transition to a wet-rated wire going back out the wall in option 2, so you don't really "save" anything there. Since the conduit appears to be (at least partly) below 8 feet (thus "subject to damage"), you'll want schedule 80, (if PVC) so you'd want to go with 1-1/4" minimum.

You could also use 1 inch EMT, though you might appreciate having more space, in practice. It is generally "not fun" to get anything very close to the maximum fill through a conduit - but you've basically got straight sections to LBs, so it should not be that bad. Though you have drawn elbows (which should be sweeps if doing that, and sweeps don't go though walls nicely, which is why we normally use LBs or a "pulling elbow" for the most minimal accessible connector.)

  • So, I went the route of PVC for the panel-to-attic run with the UF, However, because my point of entry through the soffit was not feasible, I ended up using more UF cable than intended. So, now i have a choice to make. On the other side of the house, I need to make run from Reliance box up to meet the NM-B. For some reason, I'm having trouble locating THHN for all four conductors. Is it acceptable to buy UF and strip sheath to use individual conductors and run through conduit all the way to box. I'm limited 3/4in conduit on this side, so can't imagine using UF, again... – carl12345 Sep 28 '20 at 2:25
  • No, you cannot strip UF for use in conduit - the inner conductors are not marked. THWN is dirt common - how are you "having trouble finding it for all 4 conductors"? Green, white or gray, and "any other color - the "any other color" can be marked with tape if you can't find two other colors. If "home cheapo doesn't have it" try a real electrical supply or a real hardware store. – Ecnerwal Sep 28 '20 at 2:30
  • Doh! didn't even consider going "off" nominal colors...Yeesh, makes sense. Thank you! – carl12345 Sep 28 '20 at 2:34
  • @carl12345 you seem to have this resolved, please give a check mark to the answer that helped you the most. – FreeMan Oct 22 '20 at 13:48

Just skip the conduit

Since you're running up a wall instead of into the ground, you don't need conduit for this job anyway, as UF is rated to be exposed directly to water, sunlight, etc, and a cable on a wall isn't going to get exposed to most of the physical damage sources a cable entering the ground would. (Think of rampaging weedwhackers.)

Otherwise, you're good to go in that you already plan to make the attic splices in suitable junction boxes.

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