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First and foremost - I will be hiring an electrician to handle the actual electrical stuff. I just want to know whether or not I can use some existing material.

The former home owner had a hot tub (according to the breaker box - 2 40amp circuits labeled hot tub) and we found about 100 ft of thick cabling.

The "double-breaker 40A circuit"

6-3G Non-metallic sheathing Type NM-B 600V E19816T UL

https://imgur.com/gV0D6w1

https://imgur.com/7Mbt6Ye

https://imgur.com/AnCXSWw

The electrical panel is located in our utility room in the south side of the house, but our driveway is on the north side. The existing cabling runs all the way over to the north side of the house through the crawl space and would probably have 20 more feet than needed. We would be installing the charger outside, specifically we would just pull the cable through a brick wall (will drill a small hole through the wall)

So could I pull the cable through the wall into a weatherproof box and then up to the charger via a PVC conduit? Or should I splice the wires into something that is rated for outdoor use and then pull it through the wall with some PCV conduit?

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  • please attach the pictures directly to the post ... use the button that looks like the moon and mountains
    – jsotola
    Dec 29, 2023 at 1:03

1 Answer 1

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Assuming this is actually 6 AWG copper, black/white/red/bare ground, it is actually good up to 55A - see Ampacity table, so you could use it for a 50A circuit. Which raises an interesting question of why they used heavier than needed wire for a 40A circuit (8 AWG would have been fine). So it should be OK (providing you have the service capacity for it) for use up to 40A continuous with a 50A breaker or 32A continuous with a 40A breaker.

I assume that "2 40A circuits" really refers to a "double-breaker 40A circuit" - if that is not the case, please upload a picture of the breakers.

However, you can't use this outside. NM-B cable is not rated for wet use. So you have to transition at the outer wall (or inside the house somewhere) to wet-rated cable or wet-rated individual wires. In fact, if you switch to individual wires you have to have conduit but the wire itself can be 8 AWG for a 50A (40A continuous) circuit.

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  • I have added a photo of the breaker but yeah it's like a two connected switches each reading "40". So I have reached out to an electrician but to get a fair quote I would need to ask them to install a weatherproof junction box to splice the NM-B wires to UF-B (?) and then pull that up to the charger via outdoor conduit?
    – rugbert
    Dec 29, 2023 at 17:28
  • Depends on local jurisdiction practice/inspector. Technically the splice should really be done inside the building. In practice for many things if you have a weatherproof box on an outside wall the splice can be done there (or it can be a termination itself - inlet or outlet or light fixture or whatever). A local electrician should know the local practice and therefore how to handle it properly. Dec 29, 2023 at 18:02

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