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I am running an 80A (4AWG Copper) line for EV charging in my garage. I am using EMT conduit and I need to transition through drywall. Since the studs are not deep enough (2x4) for the minimum radius turn to fit, can I put an LB conduit body on both sides of the wall to effect the transition? It seems to be code according to NEC, but it's exploiting an exception back-to-back, namely:

NEC 314.28(A)(1): for 4 AWG or larger conductors the distance from a conductor's entry to a "box" and the opposite wall must be at least 6 times the raceway size - 1" EMT in this case, so 6" - except if the opposite wall is a removable cover. So I'd be exploiting this exception twice with essentially zero intermediate cable run.

ASCII picture: 

       GARAGE
                   ---------- <--- removable cover for LB conduit body #2
                ________________
  LB conduit    | .................... 4AWG conductors
  body #2 ----->| . ____________
================| . |========================== <--- drywall
       _________| . |
4AWG .............. | <-- LB conduit body #1            
       _____________|         
         ----------  <--- removable cover for LB conduit body #1
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  • Just a comment here. At large AWG sizes Al wire is almost always significantly less expensive than Cu. You might want to price this out both ways. 4 AWG Cu wire can be frighteningly expensive.
    – jwh20
    Commented Mar 10, 2020 at 20:26
  • I priced it both ways. Al would be about 1/2 the price but I'd have to go up 2 conductor sizes (AWG #2). Works out to about $75 savings for this project, which in the grand scheme of things is not significant (the charger itself is $1,000). Which one is easier to pull? (I have not pulled conductors this large before).
    – Jonathan Baxter
    Commented Mar 10, 2020 at 20:40
  • Pull challenge is largely about how much you have oversized the conduit beyond legal minimums. Al is a smidge easier to pull, being more flexible at same ampacity, but the larger wire size will also be slightly more conduit fill. You are pulling THHN or XHHW individual wires, right? Not trying to chicken-choke a cable through conduit? I ask because lots of people don't know about individual wires, and beeline straight to cable.
    – Harper - Reinstate Monica
    Commented Mar 10, 2020 at 22:33
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    @jwh20 -- oddly enough, the wiring terminations on Tesla Superchargers are copper-only...
    – ThreePhaseEel
    Commented Mar 10, 2020 at 23:10
  • Three phase I haven’t done a Tesla, did not know that they were copper only. +. I usually stick with copper for high load devices but do use aluminum for sub panels.
    – Ed Beal
    Commented Mar 11, 2020 at 1:02

2 Answers 2

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There is no restriction to how many you use. We regularly use extra pull boxes and conduit bodies to make the job easier. It’s not cheating at all. Each one is listed for that use once it leaves the conduit body. There is nothing except cost preventing you from using them.

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  • Even if you're essentially connecting two conduit bodies back-to-back?
    – Jonathan Baxter
    Commented Mar 10, 2020 at 20:12
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    Use a close nipple the length between them doesn’t matter. Code expects they will have a nipple or pipe connected it doesn’t state the minimum or maximum length.
    – Ed Beal
    Commented Mar 10, 2020 at 20:16
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Yes, coupling them back to back like that is fine.

But I would seriously consider going another way, and that's because I don't like dead-end work, and like expandability, especially when it's negligible additional cost.

I would put a 12-space 100A subpanel to the garage near the Tesla charger. Bog-standard 3x #1 aluminum THWN or XHHW in 1-1/4 or 1-1/2 (easier pulling) EMT conduit, EMT is the ground. Then, I'd run a short #4 copper (any convenient wiring method) to the Tesla charger, coming off an 80A breaker in the sub. Why?

Future expandability. Get a second EV later? Add it (tell the Tesla EVSE not to overdraw the panel). Want to make your garage a shop? Plenty of power. Get an RV? Whatever you need.

As for cost, the wire and conduit cost will be a wash since we're running 3x #1 Al in 1-1/4 instead of 2x #4 Cu in 1". But still, it'll add less than $100 to the project, pretty negligible on total project cost, and make future upgrades easy.

It also lets you use Al wire in the way EdBeal prefers: as feeder rather than branch, and solves the "Cu-only" listing problem on the Tesla.

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  • Good idea. Exactly what I am doing :) This is part of a much larger garage upgrade project I am in the midst of. I already installed a 100A subpanel in a small room off the garage. I have ordered #1 Al MC cable which I will run from the main (200A) panel. This is about a 100' run, and the MC has to be fished through the finished ceiling of the basement - so no EMT. The 80A EV feed is 40' from that 100A subpanel to the wall of the garage between the two car bays to support charging 2 EVs down the road. The subpanel is also feeding new 20A, 120V,/240V circuits, and a 240V/30A feed for a heater.
    – Jonathan Baxter
    Commented Mar 11, 2020 at 17:06
  • @JonathanBaxter very nice! Then I'll amend my advice to bring a second 100A subpanel here. That will drop the price further since you don't even need another 100A breaker, you can just use feedthru lugs off the first panel, since all of it is protected off the breaker in the main panel.
    – Harper - Reinstate Monica
    Commented Mar 11, 2020 at 18:24
  • Interesting. I never heard of feedthrough lugs. I already bought everything I need, so probably won't go the second panel route. The charger supports dual charging mode off one 80A feed (it's smart - balances current between the vehicles depending on the discharge of their battery). And 1" EMT is already pretty fat - not sure 1 1/2" is going to look that great across the garage ceiling. If I do ever need more than 240V @ 20A in the garage It's easy enough for me to run another line.
    – Jonathan Baxter
    Commented Mar 11, 2020 at 18:58
  • Also, I haven't pulled a permit for this work yet - but it's expanded well beyond my original plan so I am probably going to do the right thing, which will mean some negotiating with my local inspector. Hopefully he won't make me rip open all the proslat that I've already run the 240V/20A through...
    – Jonathan Baxter
    Commented Mar 11, 2020 at 19:01
  • @JonathanBaxter Yeah, feedthru lug panels have lugs on top and bottom, or breaker top and lugs bottom. I figured you might've, but I figured upcycle the bought one to the garage, then get 1 more with feedthru lugs. I've heard Tesla has 2-vehicle Superchargers in the 50kw class (that you should use every other space in Supercharger stations), but didn't know 20kw tier chargers can support 2 cars. Typical Tesla... smart.
    – Harper - Reinstate Monica
    Commented Mar 11, 2020 at 19:48

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