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NEMA 14-50 8 gauge wire

Discussion in 'Model 3: Battery & Charging' started by psyrob, Jun 30, 2018.

  1. psyrob

    psyrob Member

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    My electrician who has done lots of other work at my house says to install the Nema 14-50 with 8 gauge wire, not 6 gauge like the Tesla site says. I know nothing about electricity other than it can kill you. Is this ok? He said 6 gauge is for runs of over 150 feet or something like that. The 14-50 will be about 35 feet from the electrical panel, 200 amp total box
     
  2. PJFW8

    PJFW8 Red Menace may hurt me

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    8 gauge wire pulled in conduit would be OK, if you are going to charge at 32 amp using a 40 amp breaker. I would push for six gauge and a 50 amp breaker. This will allow the option of 40 amp for other plug-in chargers and would allow wiring of the wall charger up to 48 amps if 6 gauge wire is pulled in conduit and a 60 amp breaker is used. It is good to be open to future options.
     
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  3. timk225

    timk225 Active Member

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    35 feet, 8 gauge should probably be ok. My run from the breaker box is 60 feet of 4 strand 6 gauge wire to the electric oven outlet, then a 15 foot Camco extension cord. I would say to use 6 gauge for anything over 50 feet, or voltage drop could be an issue, and warm wires.

    My phone app when charging shows 241 to 244 volts at a 32 amp draw.

    If you were using a 1st gen charge adapter that pulls 40 amps, I'd say to go with 6 gauge for any length of wire, but if you're using the 2nd gen adapter that only draws 32 amps, you should be fine.
     
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  4. TexasEV

    TexasEV Well-Known Member

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  5. flashflooder

    flashflooder Member

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    Don’t skimp on the wire. Not worth it.
     
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  6. KJD

    KJD Supporting Member

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  7. P85_DA

    P85_DA Supporting Member

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    if you are running conduit already why not just run #2 and be ready for HPWC?:(
     
  8. patrick40363

    patrick40363 Member

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    I ran the biggest wire I could fit in the conduit which I think was #3. Don't cheap out on the wire. You may want to upgrade the charger at some point so you will have the right size installed. I would have put #2 in but it wouldn't fit.
     
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  9. psyrob

    psyrob Member

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    I'll be using the 2nd generation adapter, as I think that is what comes standard with the car, which I take delivery on July 14th. I am not trying to be cheap, I am just following what this electrician said. I showed him the Tesla install guide, and he gave me the feedback/advice in my first post. I think he said he would put in a 50 amp breaker too. I am just out of my depth with electrical work, so all advice of yours is appreciated.
     
  10. P85_DA

    P85_DA Supporting Member

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    Go with #6 not 8 ...not sure why your electrician is pushing back and 35 feet is still a good run and the #6 will run cooler o_O
     
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  11. iluvmacs

    iluvmacs Member

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    If it's 75°C or 90°C rated wire in conduit (NOT Romex), then 8 AWG would be up to code. But I'd still put in 6 AWG to not lose as much power to heat. Just tell him you're happy to pay the difference.
     
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  12. eprosenx

    eprosenx Member

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    Testing 1.2.3... The forum won't let me post something I just wrote. I wonder if the content of the message was the issue?
     
  13. eprosenx

    eprosenx Member

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    EDIT: Cloudflare is blocking this post if I quote NEC code sections in numeric form so I apologize for the below reading a bit weird, it would not otherwise accept my post...

    I am kind of surprised at how often on this forum we beat up this same exact topic over and over again. Electricians are bound by the National Electric Code. It has very specific requirements for safety reasons. Generally the code is somewhat conservative and so I would not have any issue using any code compliant installation. Going a little above and beyond is fine, but definitely not required. The real reason to go above and beyond would be because you intend to make changes to your installation later that may have other requirements.

    So first off:
    The source of truth for wire sizing (in the 2017 version of the code) is table "three hundred ten period fifteen B 16". You can register for free access to the National Electric Code from the NFPA web site to read it for yourself.

    So that you don't have to register here is a handy copy of it with a bunch of the relevant code all in the same spot:

    http://www.barr-thorp.com/wp-content/uploads/2011/04/digest-176-nec-tables.pdf

    You can see that 8 gauge copper wire is rated for 50 amps if you are allowed to use the 75c insulation ratings. If you are using NM wire (Romex) it must be run inside the wall and there is a limit that says you must only use the 60c sizing column. So #8 AWG is NOT ok on a 50 amp circuit if using Romex. If the wire is run in conduit or is metal clad wiring then you can use it because you can use the 75c rating.

    To the distance comments- I have not read the NEC voltage drop sections in depth, but from what I understand, the voltage drop sections are guidance and not actually rules. It is good practice to follow, but not a safety hazard. More of an efficiency issue and if voltage was low enough it could make some appliances run worse or not have as long a life span.

    To others comments: Yes, you could even use 8awg romex (NM wire) on a 40 amp breaker using the NEMA 14-50 receptacle and be totally fine and code compliant with your Gen 2 UMC, but I would not recommend this since a UMC gen 1 would be a problem (since it takes 40 amps) or some future other charger might be the same (note that EV's are considered continuous loads and so you must size the wiring and breaker 25% larger than their rated ampacity). The Gen 1 UMC draws the full 40 amps and so it must be on a 50 amp rated circuit.

    But with all of that being said, I would probably run #6 anyway (that is what I did) since it is probably a somewhat minor cost delta and it gives you a little more flexibility. Your car will be one of the largest (if not the largest) power consuming draw in the house and so a little more efficiency (less line loss) would not suck. Others have pointed out that with #6 wire (if in conduit) can be used on a 60amp circuit to feed a HPWC which will then give you 48 amps usable for the Model 3 which is the max the Model 3 can make use of. I also did this for my wall connector.

    To the comment of using #3 wire: That would be a large cost delta since you would need larger conduit and wire plus it is a royal pain to work with. It would not fit under the terminals of the receptacle or probably the breaker, so I really would not recommend this route unless the specific placement of the receptacle is exactly where you would later want a wall connector *and* you were planning to install a wall connector later. Copper is super spendy right now!

    So yes, your electrician is correct as long as he was planning to use wire in conduit and not just Romex (NM) cable.
     
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  14. psyrob

    psyrob Member

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    eprosenx:
    Thanks for your detailed analysis. To some degree this is still all French to me, but your last comment I understand! The electrician told me he would run the wire in conduit. I am thinking of going with him, as he has wired my whole house, upgraded my panel and wired two outside structures on our property over the years, so he is a known entity and I trust his prices.
    Thanks all for your comments
     
  15. eprosenx

    eprosenx Member

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    Also to this comment above- There is no reason to limit yourself to a 40 amp breaker if it is 8 gauge wire in a conduit. You can do a 50 amp breaker per my comments above. If it was Romex (NM cable) of 8 AWG you would need to limit it to a 40 amp breaker (but still legal to hook to a NEMA 14-50 receptacle if you only intend to hook up a UMC Gen 2 which only pulls 32 amps).
     
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  16. eprosenx

    eprosenx Member

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    Determining conductor size is *not* a game of "guessing". It is done by applying the tables from the national electric code that have been honed over the decades. There are tables and formulas for all of this (including the voltage drop piece which is not a hard code requirement, but a recommendation in the code).

    Warm wires are fine btw. All wires under load warm to some degree and this is an expected condition factored into the NEC ratings. What you don't want is hot wires. If your wires do not warm slightly you are wasting money on wire (though yeah, since EV's draw a lot of power for long periods of time less energy loss is a good thing - so bigger does not hurt).

    If you have a UMC Gen 1 you need a branch circuit and breaker rated to 40 amps continuous, which means you have to calculate them as if they are 50 amps. If you have a UMC Gen 2 you need to calculate it as if it is 32 amps continuous which means you need a 40 amp breaker and conductors. Though generally I would always prefer to put a NEMA 14-50 on a branch circuit and breaker rated for the full 50 amps.
     
  17. eprosenx

    eprosenx Member

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    Copper wire is crazy expensive right now. Thats a good reason not to go too overboard. Other good reasons are that you must calculate your conduit fill. #2 would require a much larger conduit than #6 or #8. Plus #3 AWG copper is the largest conductor you can fit under the terminals of the Wall Connector.

    Yeah, I don't mind future proofing myself if I think there is a real chance I would do something different. Though generally the location you would run wire to for a NEMA 14-50 is low on the wall near the floor, and the place for a Wall Connector is much higher since the cable hangs off the Wall Connector. So I don't generally see a lot of value in running the thicker wire since you would be likely to need to switch it out anyway (unless your run is a long way from the panel in a difficult area to run wire and so perhaps if switching to a Wall Connector it would make sense to splice the wire and extend it up higher to a Wall Connector).
     
  18. ⚡️ELECTROMAN⚡️

    ⚡️ELECTROMAN⚡️ Fritterer and waster of hours in an off hand wayer

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    Don’t buy a Tesla and the skimp on the wire. Buy a Bolt and skimp. What’s the price difference? $30? $100? If it’s a $100 I would skimp to get it down to $30. But that’s just me.
     
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  19. a.void

    a.void Member

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    Thanks for this level of detail.

    I'm using 8AWG Romex that shows rated for 90C. This is run through walls (inside).

    I have it wired up now to a 40a breaker, but I was thinking of putting in a 50a breaker for the Tesla
    I use the same 40a setup on our PHEV with a 32a Siemens Versicharge without issue.

    Link to cable:
    Southwire 125 ft. 8/3 Stranded Romex SIMpull CU NM-B W/G Wire-63949202 - The Home Depot

    Product documentation shows max Amperage on the cable @ 40a, so I was thinking the UMC1 would work.
     
  20. TexasEV

    TexasEV Well-Known Member

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    Why not just folllow Tesla’s installation instructions as posted above (post #4). They specify the wire and breaker sizes for a NEMA 14-50 outlet for the UMC. Tesla has a similar document for every outlet type, linked from the home charging page. Don’t try to reinvent the wheel, RTFM instead.
     
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