NM-B wire and conduit through concrete block wall

[coleman10]

Been reading online about NM-B and conduits and when to use it or not use it and it seems like everyone has their own interpretation and can back it all up. Seems like there’s code and common sense and some mixture of both.

Here’s what I’m doing. I’m installing a transfer switch that will be recessed in the wall. It will be hooked up to my breaker panel on one side and to an outdoor, metal, weather proof inlet box. The wire to the panel will be run in the wall for about 6 inches and then through the concrete block wall, terminating inside the inlet box. The box can get wet from time to time if it rains, but no water should get in. It will also be sealed on the top and sides with silicone. The wire would be run through the back of the box.

I picked up some 10/3 NM-B for the transfer switch to inlet connection. I would assume for weather protection that it should be in a conduit, but also that it must be secured. If it’s in a conduit, it wouldn’t be secured on either side. I don’t think it’s allowed to run the wire through the concrete to the outside with nothing around it (maybe you can). Perhaps the wire could be secured with a clamp and no conduit on the switch side and only run the conduit through the wall and into the inlet box for weather protection. This way it’s at least secured on one side and protected from movement. For conduit, I would be using PVC.

Thanks, everyone. I have a tendency overthink and over-engineer things so I’m sure there’s a very simple answer for this.

 

[TRWham]

I would just run UF cable. It can be used indoors just as NM is, but is also good for outdoors and wet locations without conduit.

 

[coleman10]

I would just run UF cable. It can be used indoors just as NM is, but is also good for outdoors and wet locations without conduit.

And can that legally be run through a block wall with no conduit?

 

[TRWham]

And can that legally be run through a block wall with no conduit?

Yes. It is treated just as NM under article 334 when used as sheathed cable within a building. You can fish it through cavities in block walls, but cannot bury it in poured concrete.

 

[coleman10]

Yes. It is treated just as NM under article 334 when used as sheathed cable within a building. You can fish it through cavities in block walls, but cannot bury it in poured concrete.

Thanks. UF isn’t readily accessible, unfortunately, but that would be an option. I think my best bet is to use the NM, clamp it on the switch side and just put sch 40 through the block to protect the wire. I was reading that the inlet box is not considered a wet area so NM should be okay. If water should get in (highly unlikely), since the conduit is not side to side, no water will get into the switch. Conduit fill chart shows that 1/2” sch 40 should be good.