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HPWC on 40A circuit: amperage to charge at?

Discussion in 'Model S: Battery & Charging' started by davesm, Feb 23, 2016.

  1. davesm

    davesm Member

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    I apologize if this exact question has been covered already.

    The electrician installed our HPWC today, off a circuit breaker that is labeled 40A. He was certain that he set the dip switches for a 40A circuit (which I had thought should charge at 32A), but the car was charging at the full 40A. I asked him if that was OK, and he said it was fine. I then called the guy who did our delivery orientation yesterday and asked him the same question, and he said it was fine as well.

    My understanding is that it should charge at less than the amperage that the circuit breaker is labeled for, and my question is that if I set the car to charge at, say 36A, am I OK simply leaving it that way? Or do I really need to set it back further, or am I really OK at the full 40A? FWIW, this is a relatively new house with 400A total service, and he installed the wiring to the HPWC today.
     
  2. msnow

    msnow Active Member

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    Are you sure it's not labeled at 50A?
     
  3. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    There are some 40 amp breakers capable of sustained 40 amps (they're special order though). Normally the breaker should be 50 amps for a 40 amp sustained load. If he set the dip switches at 40 amps, that's for a 50 amp breaker.
     
  4. davesm

    davesm Member

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    Yes - see below. Is there any way to tell what's the highest continuous current it can handle? And is worst case that it will trip and interrupt charging?

    [​IMG]
     

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  5. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    No, the worst case is that the wires will heat up and cause a fire.
     
  6. MP3Mike

    MP3Mike Active Member

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    Since he has the wrong breaker in for how the HPWC is configured I would question his other work too. What gauge of wire was used and what is the length? (That would tell us if you just need to get the breaker replaced with a 50A breaker or if there is a bigger problem and you either have to set a lower charge rate or get the job re-done.)
     
  7. Kbra

    Kbra Member

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    That's dependent upon wire gauge rather than breaker size. Dave is correct that the likely effect will be a breaker trip, assuming the 40a breaker isnt designed for a steady 40a load. (This assumes the appropriate gauge wire was used for the install.)
     
  8. msnow

    msnow Active Member

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    Dave, was this a Tesla approved electrician? I wasn't aware of the special order type of breaker Jerry mentioned and I don't know if this is one of those but me and everyone I know has a 50A breaker. Please check this out further.
     
  9. davesm

    davesm Member

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    A little more context: The circuit breaker and wiring to the garage was installed when the house was built five years ago (with the intention of being used for an EV some day!). Today, the electrician simply installed the wiring from the end point of the original wiring to the HPWC (I don't know the gauge of the wire he used but see below for a picture of the wire he installed which had a thick metal cover). The electrician was recommended by another forum member, has installed a number of these before, and I believe the only error he might have made today was to use the wrong dip-switch setting.

    My presumption is that the original wiring was also more than a sufficient gauge (most of this house was over-engineered), and my question is whether there is a real safety risk if I leave the car at 36A? (presuming that leaving it at the full 40A could be a safety risk?)

    wiring.JPG
     
  10. msnow

    msnow Active Member

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    Dave, don't you think he should install a proper 50A breaker? They're cheap.
     
  11. MP3Mike

    MP3Mike Active Member

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    If the wiring was sized for a 40A breaker that means you shouldn't draw more than 32A continuously. The risk is that the wires get hot and start a fire.

    Don't take a chance, either set the HPWC for 32A charging or get the wire gauge inspected to see if it can handle a larger breaker and change out the breaker.
     
  12. linkster

    linkster Member

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    +1

    I would verify the wire gauge. In the meantime, I would set the dip switches for a 40A circuit that will correctly limit charging to 32A.
     
  13. davesm

    davesm Member

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    Would be too expensive to change (or even fully inspect) the wiring between the circuit panel in the basement and the garage. So I just set the charging to 32A...

    Thanks for the advice!
     
  14. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    To make it code compliant based on the existing install, you must reconfigure the HPWC to the 40A DIP switch setting. As installed, it's an illegal install because of the breaker size mismatch with the installation instructions.

    As long as there's nowhere along that circuit where there is any NM cable (Romex), make sure the wire is #6 or #8 and swap the breaker out if you want 40A charging. If there is NM cable along the path, only #6 is acceptable.

    - - - Updated - - -

    Fair enough. :)
     
  15. mikeash

    mikeash Active Member

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    If the car is charging at 40A then your installer didn't configure the HPWC for a 40A circuit, they configured it for a 50A circuit. At a minimum, dial your car down to 32A for now.

    Beyond that, I'd either reconfigure the HPWC, or if the wiring is suitable, replace the circuit breakers with 50A breakers.

    Reconfiguring the HPWC is easy. Disconnect the power first, crack it open, and set the switches according to the manual. Should take just a few minutes, and then you'll be in business. 32A charging is probably sufficient, that'll take you from zero to 100% in about ten hours.

    If the wiring is suitable, replacing the breakers shouldn't be hard, and will let you charge at 40A. If the wiring is not suitable, then it's going to be a bigger job....
     
  16. brkaus

    brkaus Member

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    If your good with 32a, stick with it. Would be safe!

    You could flip the breaker off, take off the cover, and check the type/size of wire used to see if switching out for a 50a breaker would be allowed.

    The required wire gauge was mentioned up-thread.
     

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