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NEMA 14-50 service to detached garage

tebling

Member
Mar 23, 2017
32
37
Woodinville, WA
My Model 3 is arriving soon, and I'm in the planning stages of a DIY install of 50A service to my detached garage from the main panel in the house. Garage is currently serviced by 20A from the main panel, and there's no garage subpanel. The wire run would be about 80' between the two buildings.

From house to outside:
New 50A breaker goes into the 200A main panel. There's room, and I'm not even close to running 100A concurrent, much less 200.
6/3 NM-B "Romex" from breaker, through punch out at bottom of panel (via Romex connector), fished behind drywall down to near floor level.
Pull the Romex into weatherproof PVC junction box attached to side of house, through some kind of PVC bushing.

Underground run:
Splice Romex in PVC junction box to 6 AWG THHN/THWN red, black, and white conductors. Question: what's the best way to splice here? Polaris connectors look like a good option.
Exit downward from box into 80' run of 2" schedule 80 PVC from house to garage at or greater than 18" burial depth. There will be three 90 degree bends in the PVC (two vertical and one horizontal).
Pull THHN conductors as well as 10 AWG THHN green for ground.
Question: Can I pull the THHN green into the house behind drywall to the panel and leave the Romex ground wire unused?

From underground to inside garage:
PVC comes up vertically from below grade along the garage exterior wall to a right angle PVC LB conduit body for wire pulling, and entry into garage wall.
Short span of 2" PVC through wall to meet another right angle LB on garage interior, oriented to exit upward.
More 2" PVC running vertically up the garage drywall (surface mount) to at least 48" above floor, entering 4" metal receptacle box attached to a wall stud. Will need a threaded PVC plug to go into box with lock nut. I hope that's not too hard to find in a 2" to 3/4" reducer.
NEMA 14-50 in box with 4" "exposed work" cover plate.
All four THHN wires are pulled through all of this.

Does all this sound right?

I'd love to run the THHN all the way to the panel in the house, but conduit won't work there. So am I right in thinking that splicing THHN to Romex is the way to go here? I don't really like the idea of the exterior box, but not sure what else to do.

Thanks!
 

davewill

Active Member
Feb 5, 2014
1,828
2,074
San Diego, CA, US
Maybe. Some places won't let you run two circuits to an outbuilding. I'd be tempted to run a 80-100a circuit to the garage replacing the 20a circuit and terminate in a subpanel. Then run the rest of your garage circuits from that. That will leave you more flexibility in the future and gives you a cutie in the vicinity of the garage.
 

tebling

Member
Mar 23, 2017
32
37
Woodinville, WA
Maybe. Some places won't let you run two circuits to an outbuilding. I'd be tempted to run a 80-100a circuit to the garage replacing the 20a circuit and terminate in a subpanel. Then run the rest of your garage circuits from that. That will leave you more flexibility in the future and gives you a cutie in the vicinity of the garage.

I should have stated earlier that this is a rental - and yes, the landlord is thumbs up as long as I'm paying. So I'm not too interested in expanding the scope of the project beyond the short term. If it were my own place, or if the landlord wanted to pay me, then it would be a different story...
 

BerTX

Supporting Member
Supporting Member
May 2, 2014
3,505
3,647
Texas/Washington
This is bad advice I'm going to give. I'd ignore it if I were you.

In a rental where you are footing the bill, I'd consider going cheap and not worry much about code. I'd consider installing the NEMA 14-50 outlet on the outside of the house, to code and inspected. The Mobile Connector does not use the common (white) wire, so build an extension cord using 2 conductor (+ ground) outdoor cable to run to the garage, reasonably protected from damage, perhaps overhead, and label the end as TESLA ONLY. When you move, take the wire with you.
 

tebling

Member
Mar 23, 2017
32
37
Woodinville, WA
This is bad advice I'm going to give. I'd ignore it if I were you.

Thanks for the advice. I don't necessarily think it's bad advice if I was looking for the ultimate budget solution.

There are a few reasons I want to do a quality job: a) we're going to be in this house at least another year and a half, b) it's good practice for when I do the job for real on my own house someday, and c) safety first!

In other news, I've changed tactics slightly based on some advice from my dad. Instead of dropping Romex from the panel inside the wall, I'll punch through the back of the panel to the exterior and do PVC for the entire run. No junction box, no Romex, no splicing, and I can run THHN all the way. It'll be a bit cheaper as well. The only extra effort will be painting the conduit to match the house where it runs down the wall from panel height.
 
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davewill

Active Member
Feb 5, 2014
1,828
2,074
San Diego, CA, US
I should have stated earlier that this is a rental - and yes, the landlord is thumbs up as long as I'm paying. So I'm not too interested in expanding the scope of the project beyond the short term. If it were my own place, or if the landlord wanted to pay me, then it would be a different story...
Understood. Do still be aware that code might or might not allow your to run a second circuit to the outbuilding.
 

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