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I'm looking to purchase and install a Tesla home charger since I'm tired of charging on a 120V outlet. I've been reading a bit and think I have a plan, but since this would be my first time doing any electrical work I want to make sure I'm not doing anything stupid.

First: For a 48A max continuous load, I need to provision a 60A circuit. That would require #4 NM wire, but since 4/3 NM wire is extremely expensive everywhere I've looked, I was thinking to do three separate THHN/THHW-2 wires. Is that the right way to do it? Should I use #6 THHN since those have the >60A ampacity required for the circuit, or would #4 be prudent?

Second: I'm going to be running the wire from my main panel through the crawlspace about 50ft to the other side of the house where the charger will be installed. For this crawlspace run (largely perpendicular to the floor joists, I figure I've got three options:

  • Just staple the three conductors to the bottom of the joists (seems like a bad idea?)
  • Drill holes through nearly 40 floor joists and run the conductors through those holes (presumably the holes would be halfway up the joist)
  • run some kind of conduit (PVC or flexible aluminum seem the most attractive) to protect the conductors and said conduit to the joists.

Third: Where the cables exit the crawlspace (through an exterior wall), I was planning to run them through into a length of conduit connected to an LB conduit body and then up through conduit into the Tesla wall charger. I think this is what I've seen done on other exterior EV charger installations, though I haven't seen what goes on behind the wall. Anything specific I should plan to do for the move from crawlspace to exterior?

Appreciate the input.

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    How long is the run?
    – DoxyLover
    Nov 29, 2021 at 7:17
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    Keep in mind that the Tesla charger is NOT rated for AL conductors so you will be paying a premium for the copper. Nov 29, 2021 at 7:54
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    Also use #4 wire. There’s almost always some derating factor involved so for a 60A breaker for an EV charger will need to be #4. Nov 29, 2021 at 8:01
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    Can you post a photo of the label on the inside of the door of your breaker box please? Nov 29, 2021 at 12:46
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    @SolarMike, thanks and I understand the sentiment but given that this is the "DIY" StackExchange, that's not super helpful :P
    – Aaron J
    Nov 29, 2021 at 19:03

1 Answer 1

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The 48A Tesla charger requires a 240V 60A circuit. That's 2 conducting wires plus ground. There's no need or use for a neutral wire. Per the installation manual: "use minimum 6 AWG, 90° C-rated copper wire for conductors." The appropriate ground wire size is 10 AWG Cu. Dual-rated THHN/THWN-2 installed in conduit and attached under the joists would be suitable. These wires must always run in a raceway or conduit (unlike NM cable that you see stapled to joists in dry indoor locations).

For a 60 ft run I would stick with 6 AWG Cu. The one-way distance for a 2% voltage drop is more than 115 ft. Assuming 0.5 ohm per 1000 ft you will burn 70W in resistive losses or 0.6% of the transmitted power. There's no need to install 4 AWG Cu wire unless you anticipate a second charger and expect to run both chargers all night each night (not a common situation, but I don't know your commute).

For a DIY project I would use PVC-40 since you don't need special tools to work with it and per your description the installation is not subject to physical damage. If the conduit emerges from the ground or runs under a garden bed I would use PVC-80. Two 6 AWG conductors plus one 10 AWG ground will fit in 3/4" PVC-40 (24% fill). The same conduit can handle 4 AWG if you needed to upgrade down the road (34% fill).

A strict interpretation of code section 422.31(B) says you need a disconnecting means (line of sight or lockable). My local AHJ is not requiring this for a 240V 48A charger as implied by 625.43.

Others should comment on the wall penetration.

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  • Is there a reason you want to use rigid PVC instead of ENT for this, given that it's more or less an indoor space? May 10 at 1:48
  • I have no experience using ENT so I hesitate to recommend it. From my limited understanding, the exterior portions of the installation would need to use something else. But ENT may be suitable under the crawl space. Please comment on how best to apply it.
    – Stanwood
    May 10 at 2:39
  • Yeah, you'd have to transition to PVC (a standard cemented coupler works just fine for this, ENT is compatible with rigid PVC fittings) for the outdoor portion of the run, but that doesn't seem to be the source of the OP's issues May 10 at 4:25
  • #6 copper is a bit spendy, I'd suggest looking into aluminum wiring, instead. It's perfect for this type of project. I don't know what the equivalent AL wire size would be, but it'd be bigger, yet cheaper.
    – FreeMan
    May 10 at 17:10
  • @FreeMan For the crawl space run, 4 AWG Al would be suitable (65A allowable at 75C) so long as the breaker has CO/ALR contacts and the installer knows how install Al correctly to avoid oxidation. The Tesla EVSE has Cu-only contacts so this requires a transition to Cu in a junction box. A natural setup would be to install a small sub panel since these are routinely fed with Al SER. The additional components (panel, breaker) will eat into those cost savings.
    – Stanwood
    May 11 at 14:49

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