Installing Tesla charger with pre-wiring

Hi! I have a question about the best way to install Tesla charger with existing pre-wiring, or whether it needs a new wiring.

I have just bought a new construction house that comes with a 30A pre-wire for car charger. Now it's supposed to be 50A and my builder is going to fix that, so let's assume it is 50A pre-wire.

I contacted one Tesla recommended electrician and they suggested against using pre-wiring for many reasons:
1. 50A is a slower charge and won't be able to use full capacity of the charger at 60A.
2. Will need to do splicing and will be a weak point of the system reliability.
3. Will need conduit.

I am not concerned with #1 first of all. A bit slower charge is fine.

I'm not sure about #2 whether it's really needed. The electrical box that is located where my charger is going to be has around 12 inches to extend beyond the outlet point. So I thought that should be enough to wire into Tesla charger directly.

I am also not sure why a conduit is needed for reason #3. I read online that as long as my pre-wiring uses Romex wire then it should be fine without conduit. And from what I can tell, it is Romex wire, and should still be a Romex wire when my builder fix to be 50A.

So I want to ask for more opinions here whether it is really bad to use pre-wiring? Are splicing and conduit real concerns? Or my electrician just simply wanted to spice things up for a more expensive quote?

Thanks all ahead for awesome replies!


  • 50A circuit: 40A maximum
    60A circuit: 48A maximum

    Your car, unless an early MS with dual chargers, cannot utilize more than 48A. Charging at 40A overnight (~7h from 10% to 90%) is more than ample for most users.
  • Oh yeah, and that electrician is trying to rip you off.
  • If you are pre-wiring the house one would assume the builder is using a licensed electrician. The wire they install will be able to handle the load, and they know where conduit is needed. I would suggest, however, that if they have not started that you go with a 60A line instead, as this will allow you to fully utilize the HPWC either now, or in the future, if you upgrade. Yes 60A wire costs more, but you can save money by using 2-conduit wire instead of three - neither the mobile connector or the HPWC utilize neutral (if you stick with the 50A line, also just use 2-conduit.) All that is then required is installing a NEMA 6-50 plug instead of the 14-50, Tesla offers both connectors, and the builder needs to install a plug of some kind anyway.

    As to your distance question, since you are pre-wiring just have them put the plug wherever you need it. The cable length on the Mobile Connector is 20-feet. If you go with the HPWC (18-foot cable) I would have it hard wired even if you only go with 50A line. I bet the builder will give you a very reasonable price to have his electrician connect it for you.

    Totally agree with @rxlawdude, your electrician is trying to rip you off!
  • BTW, no matter what you connect the Mobile Connector too, it is limited to 32A maximum draw. The HWPC on a 50A line will draw 40A, and on a 60A line will draw 48A.
  • I'm surprised they didn't try to convince you that you need a new breaker box! Yes, Tesla-sponsored electricians know that "they've got a live one" when a new owner calls in. Call a private electrician who does his own work. Mine charged $275 to install a Tesla supercharger (So. Florida.)
  • Yes, never say 'Tesla' to an electrician. Eyes turn into $ signs.....I initially did that for my quotes.....were all around the $1k mark. Then called and said I wanted a 60A line added to house electrical. $300. When asked to connect to HWPC, it went to $350. That one was right opposite of main electrical box through the wall to the garage. The second one was a good 20' further so cost a tad more.
  • Tell the electrician that you're looking at buying a used Leaf but want at least 40 amps just for future expandibility.
  • Any electrician that would jack prices just because you own a Tesla lacks credibility and I doubt they have been in business for longer than a year. The stories about being sized up and scammed are not credible for electricians that want to stay in business for long.

    Code vary across the nation and the world, local codes may be more strict than the national code.
  • ok, Im not an electrician but dealt with this nightmare enough. you need a 60A to utilize the the charging capacity of the 48A and you also need at least 6/2, preferably 6/3 90C wire to handle the current that's why it's recommended as specs in the tesla install manual. the tesla "preferred" electrician in my area was going to install a 50A breaker on a 8/2 wire which would have been slower obviously and only using a max of 40A charging. He was going to charge me 3k. He didn't show up the day of the install so I hired another non tesla electrician, half the price and 60A 6/3 wire. They will hose you if they smell blood
  • The electrician company that I contacted is actually Tesla recommended company and I have used their service 5 years ago when I installed Tesla charger in my previous house. That went fine as I needed a new wiring so they did the job with $810 which is reasonable to me. So it's surprising to me too why they would try to sell me a new wiring on top of my pre-wiring. I smelled fishy and asked a lot of questions about the reason why pre-wiring is so bad, which they answered with reasonable reasons except the part with splicing and conduit.

    I do want to make sure though, my electrician said Tesla Wall Connector needs more than 12 inches of wiring from the outlet point to connect to it. Is this true? Someone already mentioned that Tesla charger can just sit on top of where the pre-wire ends, so that implies it should work fine with 12 inches wiring, but I want to make sure I translate correctly.

  • It is conceivable (possibly even 'likely') that the pre-wiring was not done properly sue to the shoddy workmanship found in most new houses. This doesn't happen to be in CA does it?
    The builders might have left insufficient extra tail on the pre-wiring.
    Nobody on this forum can really know about this. Another opinion from a good electrician who can actually see what is there is necessary.
  • No, I'm in WA. Are things that bad in CA with builders?

    I did contact the other Tesla recommended electrician and they told me they could use my 12 inches wiring fine by just mounting charger right on the electrical box. They also don't seem to be concerned with not having conduit for the pre-wiring. But I also want to get some more opinions here as well from someone who has already dealt with installing Tesla charger with pre-wiring just to be sure, so I can compare information from many sources not just from 2 electricians.
  • If you had a 2nd gen hpwc charger, (eBay), you could charge at 80 amps, but you would need to feed that off a 100amp breaker, and have it hard wired.
  • I can understand why they need 12 inches beyond the outlet because they need to reach the terminals in the charger but saying they need to splice or rewire is BS. just move the outlet up or down on the wall to gain your 12 inch slack, especially is its a new build and the drywall isn't up yet either way, easy fix
  • Thanks @mislead for the reply! My house is already finished though. However, the outlet position is already in a good position where Tesla Wall Connector can just mount on it directly. So I'm not quite sure what do you mean by moving up or down the outlet to gain 12 inch slack. Could you help elaborate on that more?
  • if they didn't leave enough wire at the receptical end the there might not be enough to put through into the charger as it needs another 6" at least to wrap around to the terminals. if you need more slack then remount the receptacle(or box) further up the wire to gain the extra length......hard to explain, do you know what I mean
  • Conversely, that means the charger can move up or down to gain the extra length as well, am I correct? I'm not quite sure why you only mentioned moving up or down the receptacle box. Is there a reason you didn't mention moving the charger up or down?

    I think it's hard for me to understand what you say without the visual unfortunately. First of all, what's the entry point for the wire to go into the charger that you tried to suggest? I'm not quite following what do you mean it needs at least 6" to "wrap" around to terminals. So knowing the entry point into the charger would help me able to follow your visual more.

  • yes it depends where the wire enters the charger. if the wire is coming down from the roof(attic)then you can move the charger up closer to the ceiling to gain a few more inches and vice versa if the wire is coming from the basement. usually when the prewire is done they will terminate it in an electrical box for code. the question is if they left enough wire in the electrical box to make it to the terminals on your charger, right? or am I missing something
  • Just to be on the same page, here're some photos of my garage:

    Electrical box:!AiQMwQM5L2NhwcdcZlhxqkIG64PeeA?e=7lmtve
    Farther view from electrical box with cover:!AiQMwQM5L2NhwcdDlN0588Y_qCKepQ?e=I2Bs4b

    So yeah, it's correct that the question is if my build has left enough wire in the box. What I'm not sure is whether the charger can just mount on top of the box itself so the wire can enter from its rear with minimal length requirement?
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