I am trying to come up with a wiring solution for a NEMA 14-50 240V outlet in the garage for an EV. Specifics of my situation:
Max charging current will be 32A, so I need #8 wire.
Breaker box is on an exterior wall, at a wire length of 90-100 ft from the outlet.
I'm proposing to run the first 70' through the attic; then pop out for the last 20' or so. I had originally thought I'd just run 8/3 NM Romex all the way, but found out to my dismay that Romex cannot be used in outdoor conduit. Then I figured I might strip away the sheath and treat it as THHN outside, but one of the answers to the linked question made short shrift of that idea.
So now I am faced with the following restrictions:
- Cannot use Romex in the outdoor conduit.
- Cannot remove the Romex sheath and treat component wires as THHN.
- I would rather not run conduit over the entire 90 ft run. It would involve many 90 deg turns and be a hassle to set up. Romex still looks appealing for the 70' linear length in the attic.
- UF cable over the entire run would work but be very expensive. Also, overengineered, since only the last 20' of the run is outside.
So my current thinking is to run Romex to near the exit point, and hop over to THHN/UF in a junction box before exiting the wall to the exterior of the house. The remainder to the breaker box will run in conduit outdoor. However, it will need connecting the two different conductor types with wire nuts. I am wary about doing this on thick wires, for a circuit that will have a constant 32A draw.
My questions are:
- Does this plan sound reasonable? Can someone suggest better options?
- Are my misgivings about wire nuts warranted? I looked for alternatives; it looks like bus bars could be used, or I could butt-splice wires together. I haven't investigated either of these in depth.
- If I do follow this scheme and switch to a different wet-rated solution for the outdoor run, would THHN be markedly better than UF for pulling through conduit? What if I use UF but not pull, rather build sections of conduit as-I-go? (so I'm threading it through say 5' of PVC conduit at a time?)
Also a comment/question about pricing: #8 THHN is $0.64/ft at the local home improvement store. So $64 per 100ft for one wire! $256 for 100 ft for 4 wires. I thought THHN was supposed to be cheap; how/why is it so much more expensive than Romex, which one would think has the same amount of copper? For comparison, a 125’ 8/3 Romex reel is $185.
EDIT: Adding a further restriction on my setup to address @Harper's suggestion of using thicker wire. If I am to use the only side (bottom-left) knockout available on the breaker box, I need to do a tight 3" radius turn into the breaker owing to obstruction from a fiber box mounted infuriatingly close. I have seen that only 1/2" LiquidTight metallic conduit is able to do that, and four #8 wires already is technically past the fill for that size (but thinking pushing the rules a little might be ok for the last 6" of the run?). The only alternative is drilling a hole on the top-right side of the breaker box, but I fear I might be biting off more than I can chew at that point. Space inside the box is also quite constrained, so stuffing thick wire inside and running it to my circuit breaker will be a minor challenge as it is. These breaker box constraints are why I dropped down from #6 to #8 in the first place. :-/ (Of course, found luckily that #8 is electrically sufficient for my projected need).