TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

60A Breaker -> 4 gage or 6 gage wire?

Discussion in 'Model 3: Battery & Charging' started by 1.21GW, Jul 23, 2018.

?

What gage wire for 60A breaker with Tesla Wall Connector?

  1. 6/3 Romex

    15 vote(s)
    31.9%
  2. 4/3 Romex

    24 vote(s)
    51.1%
  3. Other

    8 vote(s)
    17.0%
  1. 1.21GW

    1.21GW Member

    Joined:
    Jul 23, 2018
    Messages:
    54
    Location:
    Michigan
    I have received a few quotes to install my Tesla Wall Connector for my model 3. The biggest difference between the quotes is wire size. All electricians have their reasons, i’d like to know what you think

    My setup:
    60A circuit breaker
    48A max charging amps (wall connector setting #9)
    35 ft. From breaker box to connector location

    Wire Ampacity Ratings
    6/3 Romex = 55A
    4/3 Romex = 70A

    Contractor #1
    6/3 Romex
    NEC 240.4(B) exception allows rounding to next highest breaker size if wire ampacity is in between breaker sizes.

    Contractor #2
    4/3 Romex
    +$220 more expensive

    As a side note, what wire size are you running to your Tesla Wall Connector (HPWC)? Also I am doing the 3 wire so I can replace my HPWC with a NEMA 14-50 when I move.
     
  2. P85_DA

    P85_DA Supporting Member

    Joined:
    Apr 25, 2015
    Messages:
    2,527
    Location:
    Chula Vista, CA
    I use THHN/THWN copper ...for your setup u can get by with 6...4 is better but the contractor is gouging u on material go Home Depot buy yourself from bulk roll
     
    • Like x 1
  3. SDRick

    SDRick Member

    Joined:
    Jun 25, 2015
    Messages:
    852
    Location:
    SD CA United States
    Ask contractor number 1 where in the code does it show that you can round up both the breaker and the conductor size? I find it somewhat confusing because while you are only pulling 48A continuous and #6 NM (Romex) is rated to 55A (but possibly not continuously) .

    I have had contractors say you need #4 Romex and others say you can get by with #6 for 48A automobile charging.

    I also find it interesting that I read on the forum the conductor size for the HPWC 25' cable is #8.

    Can anyone verify any of these?
     
  4. Ejl80

    Ejl80 Supporting Member

    Joined:
    Dec 23, 2017
    Messages:
    320
    Location:
    Nj
    It is right in NEC 240.4(B) as specified in his post. Regarding which size wire, it depends on what type of wire, length of run, if it is in a conduit or not, etc. I would go #4 because the cost isn't that much more in the grand scheme of things, and it is much easier to run wire once.
     
    • Like x 1
  5. P85_DA

    P85_DA Supporting Member

    Joined:
    Apr 25, 2015
    Messages:
    2,527
    Location:
    Chula Vista, CA
    I agree go #4 ...however if you go out and buy #4 cost differential is approx 1.25/ft so for 35ft run I don’t see how his contractor is quoting 220 more:eek::(
     
  6. Ejl80

    Ejl80 Supporting Member

    Joined:
    Dec 23, 2017
    Messages:
    320
    Location:
    Nj
    Correct, even prepackaged Romex is only 50-100 more for a 50 ft roll.
     
    • Like x 1
  7. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    5,298
    Location:
    Michigan
    Go 6/3 and use 50 Amp breaker and 40A HPWC setting. Yields full charge in 8 hours (only 7 mph lower rate than 48 Amp).

    The electrician may not be aware that EV charging is concidered continuous loads, not intermittent.
    If you charge at 48A, the circuit needs to be rated for 125% of that or 60 Amps, which exceeds 6 AWG NM-B at 60 C.

    Is #6 Romex ok on a 60 A breaker
     
  8. P85_DA

    P85_DA Supporting Member

    Joined:
    Apr 25, 2015
    Messages:
    2,527
    Location:
    Chula Vista, CA
    @SDRick ...#8 is too small ...maybe for the ground ;)..but not for the hots
     
  9. SDRick

    SDRick Member

    Joined:
    Jun 25, 2015
    Messages:
    852
    Location:
    SD CA United States
    I think we are saying the same thing but NEC 240.4(B) does not mention conductor size or rounding up. I believe the rounding up only has to do with the breaker.
     
  10. SDRick

    SDRick Member

    Joined:
    Jun 25, 2015
    Messages:
    852
    Location:
    SD CA United States
    I agree #8 is too small. My post referred to the 25 foot charging cable coming from the HPWC. I thought I read somewhere that those conductors are only #8.
     
    • Like x 1
  11. P85_DA

    P85_DA Supporting Member

    Joined:
    Apr 25, 2015
    Messages:
    2,527
    Location:
    Chula Vista, CA
    I Believe so...I had a cut open UMC gen 1 cord and it had like 2 #12s
     
  12. Ejl80

    Ejl80 Supporting Member

    Joined:
    Dec 23, 2017
    Messages:
    320
    Location:
    Nj
    Agreed. Yes only the breaker can be rated up.
     
  13. eprosenx

    eprosenx Member

    Joined:
    May 30, 2018
    Messages:
    681
    Location:
    Beaverton, OR
    Contractor #1 is proposing something that violates electrical code. They are correct in that you would be allowed to use a 60a breaker on 6/3 NM cable (Romex), but you still have to make sure the load you are attaching to that circuit is 55 amps or less (or in the case of a continuous load, 80% of 55 amps which is 44 amps). EVSE's (like the HPWC) are always considered continuous loads per NEC.

    Contractor #2 is proposing a valid solution, though if using 4 AWG Romex you could even install a 70a breaker and give yourself a little more power if you ever plugged in a different vehicle that could make use of it (assuming your load calcs allow this much capacity on your service/feeder/panel).

    Other valid options would be 6 AWG in conduit which allows using the 75c rating which allows 65 amps. This is what I did. 60a breaker, 48a usable for my Model 3 LR.

    Yes, #6 AWG THHN/THWN is fine as stated, but it must be installed in conduit. If Romex works better for this application then #4 is required.

    The cable from the HPWC to the car falls under totally different rating systems. First off, it is more of a UL issue than a NEC issue I think since it is part of an appliance rather than permanently installed wiring (though the NEC does have code around it, so I am not 100% sure to be honest). But that cable is generally rated for pretty high temperatures, and most importantly, it is not installed in walls - it generally hangs in free air and so it can let off heat easier.

    #4 is probably a lot more of a pain in the ass to deal with through walls, studs, etc... This is likely not something they "keep on the truck" so they may be sandbagging a bit to cover needing to buy a spool. #6 is probably a lot more common.

    I personally would want to be able to charge at the full 48a (requiring a 60a branch circuit and breaker), but to each their own. My car charges from my daily commute in about an hour at 48a which is crazy fast. I could get away with a much slower charger, but if already spending the money on an HPWC and electrician, paying for the slightly larger wire makes sense to me.

    #8 THHN in conduit would be fine up to 50a (40a continuous which is what the car needs). I would probably recommend at least #6, but #8 on a 50a breaker, run in conduit, and with the HPWC set to position eight, 40a would be completely safe and code compliant.
     
    • Informative x 3
    • Helpful x 2
    • Like x 1
  14. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    5,298
    Location:
    Michigan
    Sure, if having the fastest speed is the main requirement, go 4/3. However, consider a 60 minute charge at 48A turns into a 72 minute charge at 40A, only 20% longer. Full range charge is 7 hours vs 8.5 hours. Not a huge difference.

    I was also a little leary of the end point of having a 14-50 outlet fed by 4 AWG wire (plus the cost of an additional 50A breaker, only $10, so really inconsequential). However, Leviton has outlets rated for 4 AWG, so I guess it's not uncommon. Maybe the next owners will have an X, so the HPWC will stay instead?
     
  15. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    5,298
    Location:
    Michigan
    Follow up thought:
    The cost of 4/3 NM-B vs 6/3 is $4.39 vs $2.15 or $2.24 a foot, even adding 5 feet of contingency, that is only a $90 difference. Maybe go with contractor 1 but specify 4/3 and a 60Amp breaker?
    NM-B Wire (Romex® Equivalents) | Wire & Cable Your Way
     
  16. rdlink

    rdlink Member

    Joined:
    Jul 12, 2018
    Messages:
    308
    Location:
    Colorado
    This thread has been very helpful to me.

    I have a very simple installation, and have been having trouble getting an electrician to my place to even give me an estimate. My charger will mount literally a foot under my breaker panel. I will have less that 5 feet of romex to run. I have a 150 amp load center, and I ran a whole house calculator that shows my load, even with the EV charger will run around 91 amps. Add to that the fact that I have TOU service with my utility, and I will set my Model 3 up to charge between Midnight and 9:00 AM and I think I am fine with a 60 amp breaker.

    My question is this. If any of you have done self install did you use ferrels on the 4 awg wire inside the charger?
     
  17. mongo

    mongo Well-Known Member

    Joined:
    May 3, 2017
    Messages:
    5,298
    Location:
    Michigan
    No need for ferrels (do you work in automation?).
    Flush mount breaker panel with NM-B in the wall?
    The problem with your install may be it is too simple that they don't want to quote because the amount they need to charge in overhead is huge compared to the actual effort. $60 in parts $ in permits $$$ in time to get permits, get inspection, drive to site twice....
     
    • Like x 2
  18. 1.21GW

    1.21GW Member

    Joined:
    Jul 23, 2018
    Messages:
    54
    Location:
    Michigan
    Thanks everyone, I'm getting my Contractor #1 quote updated with 4/3 AWG to see the apples to apples price difference. I don't think $220 price difference between contractors is only wire price. I want to run 48A and not be restricted to 40A.
     
    • Like x 2
  19. Butane

    Butane Member

    Joined:
    Apr 6, 2018
    Messages:
    71
    Location:
    Bloomington, IN
    Came here to say essentially the same thing as eprosenx did. I'll just add the NEC code sections to back up his claims about why Contractor #1 is wrong.

    NEC 210.20(A) Specifies that overcurrent protection devices "shall be sized to not less than the noncontinuous load plus 125 percent of the continuous load." This is the part we all know about for picking our breaker size.

    NEC 210.19(A)(1) "...minimum branch-circuit conductor size...shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load."

    Since these are single device circuits, there is no noncontinuous load, just the Wall connector which is by code a continuous load.
     
  20. rdlink

    rdlink Member

    Joined:
    Jul 12, 2018
    Messages:
    308
    Location:
    Colorado
    Thanks.

    While I agree that they probably won't be thrilled with the effort vs the costs to them I have not even told them the installation situation yet.

    Yes, my breaker panel is flush mounted with NM-B. Since I live in a three level row house, with the garage on the bottom level all of the wiring heads out of the top of the box, so I don't have to worry about getting into it with this installation. I can just pop out a knockout in the bottom of the box, and run it literally a foot below the panel.

    Again, my biggest concern was amperage load, but I'm beyond that now. I think this is just going to be me doing the install. Should really only take me about 45 minutes to an hour, tops.

    Like the OP I am going to run 4/3, so I can yank the wall charger and replace it with a 14-50 if/when I move.
     
    • Helpful x 1

Share This Page

  • About Us

    Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.
  • Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


    SUPPORT TMC