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6/3 cable for HPWC?

Discussion in 'Model S' started by superm1, Jul 5, 2016.

  1. superm1

    superm1 Member

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    Fremont, CA
    Is 6/3 cable fine for the HPWC with a 60a breaker?
     
  2. superm1

    superm1 Member

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    Fremont, CA
    Also, should the cable be NM-B or SE?
     
  3. zambono

    zambono Member

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    I have 6 cable for a 50 amp nema outlet I think you are going to need a 4 for 60a breaker
     
  4. whitex

    whitex Member

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    It's probably sufficient but check the code for your area as it can depend on where it's running (what conduit and with what other cables), what insulation it has, etc.
     
  5. tls

    tls Member

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    New York, New York
    It' OK only if you restrict the HPWC to charge at 48A or less (in which case, why don't you just use your UMC and save yourself some money?). Charging is a "continuous load" and you are required to size both breaker and conductor for 125% of the load (see NEC sections 210-20(a), 384-16(d), and 210-19(a)).

    That means that the maximum load you can legally apply through that 60A breaker is 80% of 60A = 48A. In other words, if you have a new car with the 48A single charger, you can just barely charge it full-rate on that 60A breaker. Now maybe I see why you're doing this. ;-)

    Now, how about that 6-3 wire?

    The terminals on your 60A breaker *may* be rated at 90C, but the terminals in the HPWC are only 75C rated. So you must use the 75C column of Table 3.10(B)16. Note that this table applies to *copper* conductors in raceway, cable, or directly buried -- if you put that 6-3 cable inside conduit, you must derate it even further.

    According to the table, the cable can carry 65A. So the maximum load you can legally apply through that 6-3, 75C or better rated cable is 80% of 65A, or 52A. So, again, you're OK for 48A charging, but no more.

    If your car has dual chargers, I'd recommend you bite the bullet, run some conduit (not that hard with PVC), and wire with #3 copper (to deal with conduit fill issues, you can safely and legally use a bare #8 wire for ground). More work, but future-proof. For single chargers, a 60A breaker and 6-3 will do.

    Whatever you do, I'd recommend against "upsizing" to larger aluminum cable. It's often not legal for use inside homes due to the flammability of the jacket, and it is very, very difficult to land it properly on the terminals inside the HPWC due to the sharp bends required.
     

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