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Charging receptacle wiring question.

Discussion in 'Model 3: Battery & Charging' started by AviP, Aug 28, 2020.

  1. AviP

    AviP Member

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    I was going to install a Nema 14-50R receptacle to charge my future Tesla CyberTruck but am posting here because the knowledge is strong amongst the Model 3 folks.

    I'm doing the job myself and I've figured out the following based on recommendations from this site: A 50 Amp GFCI breaker on one end and a Bryant 9450FR 14-50R receptacle on the other connected via 6 AWG wire.

    My question is specifically about the wire. I understand that XHHW-2 is the best choice but am having a hard time finding it in 6/3 AWG XHHW-2 CU (copper). The local supply shops do not seem to stock it. What is everyone else using? Please post your wire specs that are posted on the wire itself.

    Additionally, the receptacle is going to be outside the garage. What "IN USE" enclosures are folks using?

    TIA
     
  2. cdswm3

    cdswm3 SR+

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    Unless you are going a very long distance the type of #6 wire will not make any difference at 50A.
     
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  3. AviP

    AviP Member

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    I'm going 100 ft from the breaker.

    What are most folks using:
    NM-B
    THHN/THHN-2
    XHHW/XHHW-2

    And in AL (aluminum) or CU (Copper)?
     
  4. Sophias_dad

    Sophias_dad Supporting Member

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    #4 Sophias_dad, Aug 28, 2020
    Last edited: Aug 28, 2020
    The AL/CU question should be decided before you select a wire gauge. I'd pick CU, myself. Its much less likely to burn down your house, even if the AL is installed properly.

    NMB is really a question about whether its even allowed for the circuit, and also requires downrating to 60C temperatures. You can only officially get 40 amps continuous out of a 6AWG nmb wire, which probably isn't an issue for you because you are installing a 14-50 outlet which I think is also supposed to be downrated for continuous use. The more important consideration (for you) is that NMB has to be hidden behind walls or above drop-ceilings or otherwise inaccessible to typical human activities. I >think< you are allowed short runs of conduit, but only to get it up to a ceiling or down to an outlet. Can't think why you'd want to put it in conduit the whole length anyway.

    Obviously THHN/XHHW must be run through conduit.

    It seems pretty easy to find XHHW-2 online.... but its really expensive. I have used the latter one of these for wiring supplies, and the former for pretty much every bit of hardware I could possibly want.

    McMaster-Carr

    XHHW Copper Wire | Wire & Cable Your Way Wire & Cable Your Way sells the newer and more popular XHHW-2 cable as they offer improved insulation to the older XHHW products.
     
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  5. Rocky_H

    Rocky_H Well-Known Member

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    Oh yeah, yes, you have come to a good place. This is a good source with a lot of knowledge on this stuff.
    Thank goodness. You have gotten all the important stuff totally correct, and that's a lot better than what a lot of these questions start with. Good choice on a Bryant. Hubble, Bryant, and Cooper are all great, but Leviton is pretty crap, and is unfortunately the cheapest and what most people find.
    Yes, this is one question together. You can see what rating of circuit you want, but then you need to pick one of those two wiring methods--either copper or aluminum, and that is going to determine what wire gauge you have to use, because the amp ratings are very different. For a very long run like that of 100+ feet, sometimes people do most of it with the thicker aluminum wire, because that can be some significant savings over long distances like that, but some special things have to be done about how it's connected to do it properly. Also, the terminals of some breakers or receptacles are sometimes not rated to allow aluminum connection directly there. So what is usually done with these situations is to run the 100 feet with aluminum to a small subpanel in the garage that can take aluminum wire, and then switch at that point for the last 5 feet or whatever in copper to your outlet.
    I hadn't heard of that one, and I don't know of anyone using it. It's not necessary. I see from the ampacity tables that it's for use in the 90 degrees C rating level, but that's going to be irrelevant because residential circuit breaker types are never rated for that high a temperature anyway. They can only be used for the 60 or 75 level.
    Pretty much all installs would be either the NM-B ("Romex") or the THHN/THHN-2, but as @Sophias_dad is saying, this is determined by where you have to do your wiring run. Romex cable is for hidden places, but the THHN is individual wires pulled through conduit, which you would have attached to the surfaces of walls. So you plan where your wiring run is going to be, and that determines which wire type you need to use for it.

    Good questions.
     
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  6. Sophias_dad

    Sophias_dad Supporting Member

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    In reading the original post a bit more, it looks like you are looking for NMB with XHHW-2 as its conductor/insulation. You won't find that, and even if you did, it would have to get derated to 60C anyway.

    Another thought I had was that the current UMC is actually limited to 32 amps. Its not clear what UMC the cybertruck will have available, but its a good idea to plan for 40 amps.
     
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  7. Pricedm

    Pricedm Member

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    I would put a 60A breaker in the box, instead of 50A, and up the wire gauge to what ever code calls for, i believe 4 AWG. This way, if you decide to upgrade to a Tesla HPWC, your wiring is already set. The materials cost difference between a 60A and 50A circuit is not that much. Make sure to use appropriate conduit. At this point as we don't know what the Cybertruck will require for charging, you might just wait to install anything until specs for the Cybertruck are known.

    FWIW, I was able to source all supplies (THHN copper, black, red, and green, one gauge thinner) from Home Depot and Lowes. I had no idea what I was doing, read up on code and safety protocols, and had no issue installing a 60A dedicated circuit from my main service panel (one half always hot) to the Tesla HPWC. Good luck!
     
  8. Rocky_H

    Rocky_H Well-Known Member

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    And then you get something like this:
    No, no, NO! Don't ever recommend that for a 50A outlet install! That is wrong and violates code. You cannot do that. Code is absolutely clear on this. For a single dedicated outlet on a circuit, the breaker must be no higher than the outlet rating. It is a 50A outlet type, so you must not use a breaker higher than 50A. Period.

    If you want to prepare for something higher, you are allowed to do the wiring run with thicker wire than needed, and then you can change both endpoints (breaker and appliance) later.
     
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  9. Sophias_dad

    Sophias_dad Supporting Member

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    I agree about putting in better wiring than you need, but actually for 6awg copper in conduit, it is already rated to carry 65 amps (52 amps continuous). If OP really wanted to save some pennies and never wanted to go to a 48 amp HPWC, 8awg in conduit would JUST do 50 amps(40 amps continuous). That said, its probably worth the wire-cost-difference in energy waste(over the life of the car) having less resistance in those wires.

    I also agree that hopping right to a 60 amp breaker is a mistake. If OP does eventually switch to an HPWC, he can get a non-gfci breaker for $10-$20, depending on brand. (No GFCI needed if there's no outlet)
     
  10. Pricedm

    Pricedm Member

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    Given OP's desire to be proactive regarding home charging for Cybertruck, if it were me, I would wait until Cybertruck charging requirements are known.

    Ignore my comment about breaker size. Wire is specified by minimum AWG, which may be exceeded. Breaker must match load.
     
  11. AviP

    AviP Member

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    I was looking at XHHW-2 as it is the highest rated and has an ampacity of 75A @ 90C for Copper and 55A @ 90C for Aluminum.

    Perhaps I should have been specific about the wire. I was looking for 6/3 AWG (6-gauge, 3-conductor + ground) Copper XHHW-2 wire. For single conductor wires, there seem to be numerous options but they require a conduit. I was able to find a MC (Metal Clad) cable with Aluminum XHHW-2 conductor from Stabiloy. I could scale up to 4-gauge Stabiloy and achieve the 75A @ 90C but I was avoiding aluminum.

    Since I've been doing a re-roofing project, I have complete access to the insides of my home and would like to have this installed now rather than wait for the Cybertruck specs.

    I disagree on 60A breaker on 50A receptacle. It defeats the purpose of a breaker. It's like having a 20A breaker on a 15A toaster that could lead to a house fire. Both, the appliance and the breaker, must be matched in ampacity. But I understand what the poster is suggesting. It is to have enough power for an upward change in specs for the Cybertruck. Rocky_H did point out the correct approach.

    Also, wire in wet locations such as a garage require a GFCI breaker and W-rated (Wet location) wire according to the code in my area. Hence the W in XHHW-2. Since most full size pickups cannot be parked in a garage, I will be installing the charger on the outside wall of the garage.
     
  12. Sophias_dad

    Sophias_dad Supporting Member

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    I think you might be focusing too much on the XHHW-2 as a requirement. THWN is water rated and frequently sold in the same category as THHN(dual-rated).

    The Aluminum XHHW-2 stabiloy wire is just that... aluminum. I don't see a copper option, but I'd like to get a link.

    6-3C w/ Ground Teck 90 Cable, Aluminum Interlocked Armor, 1kV is pretty hardcore stuff.
    6-3C w/ Ground Type MC Cable, PVC Jacket, Interlocked Armor Power Cable says its XHHW-2 inside.
     
  13. AviP

    AviP Member

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