Romex through attic to exterior panel

Question

We are remodeling our kitchen and getting quotes for updating the electrical. We have received 2 quotes so far.

The service panel is on the exterior of the house opposite the location of the kitchen.

First quote calls for running UF-B through the crawlspace going through the exterior wall inside EMT that enters directly into the breaker box.

Second quote calls for running NM-B through the attic and going through the exterior wall inside EMT that enters directly into the breaker box.

The second quote is less expensive. It looks like the main reason is the cost of the UF-B vs. NM-B. When asked about the difference the first electrician said that the only option with an exterior panel is to use UF-B, because the wire is exiting the controlled envelop of the house and may become wet. The second electrician disagrees and says that NM-B is allowed to exit the envelope of the house if it is going directly into the breaker box and is protected in conduit.

Who is correct? I can see both sides.

We are in NC.

Thanks.

Answer 1

Your first quote is correct

NM-B is not rated for wet locations, and Code reflects that in NEC 334.12(B) point 4:

(B) Types NM and NMS. Types NM and NMS cables shall not be used under the following conditions or in the following locations:

(4) In wet or damp locations

Furthermore, the inside of any conduit located in a wet location, such as outdoors, is also automatically a wet location, due to condensation issues if nothing else. This is codified in NEC 300.9:

300.9 Raceways in Wet Locations Abovegrade. Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).

So, the second bid is trying to low-ball this by doing a not-so-Code-compliant job; I would point this compliance issue out to them and see how they react. Personally, I would go with neither option; either the cable would be brought up or down inside the wall cavity then enter the panel from the back, or I would have an indoor junction or pull box at where the conduit exits so that a clean transition from NM to THHN-in-conduit could be made.

Another issue...

Going through the top of a NEMA 3R panel requires special fittings, especially if it's being done with multiple conduits. Normally, a bolt-on type hub fitting is used to bring a conduit out the top of a NEMA 3R panel, but a NEMA 3R loadcenter only provides a place for one hub coming out the top, as this is presumed to be used for a service mast or such. Further wiring out the top requires the use of threaded (Myers) hubs that clamp the box from both sides and provide a rainproof seal that way, but that adds cost and requires manual knockout punching in the box top.