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NEMA 14-50 Plug from 80 Amp Breaker

Discussion in 'Model S: Battery & Charging' started by Sparktz, Nov 26, 2015.

  1. Sparktz

    Sparktz Member

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    At my father's house, he has an 80 amp breaker feeding a NEMA 14-50 outlet. Should that be safe to plug the car into?

    I know that usually you would have a 50 amp breaker feeding a NEMA 14-50, so I wasn't sure if there was any danger to having a 80 amp breaker backing that outlet.
     
  2. Sogorman

    Sogorman Member

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    Not an EE but while this will 'work' it may not be safe and is not to code. If the wire running from the breaker to the 14-50 is only sized for 50amp (as it should) the potential for the circuit to over heat or run at too high of an amperage before the breaker tripping is high.

     
  3. green1

    green1 Active Member

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    The danger isn't specific to the car, but there is a general danger in that the outlet can't handle as much current as the breaker is rated for. Is the same reason you don't replace fuses with nails, they exist for a reason, and a breaker that much over the rating it should be isn't providing the right amount of protection.
    Now if the wiring is also sized to that level, it's a great candidate for a hpwc, if the wiring is built to match the outlet then the breaker needs replacing.
     
  4. Screwbal

    Screwbal Member

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    Noob question, can you run 80 amps on a 14-50 socket? In my head I wanted to do that then get a HPWC and put a plug on it that would use the socket. I wanted a socket so if the HPWC ever fails I can just unplug it and use the 14-50 socket for the charger that comes with the car.
     
  5. mikeash

    mikeash Active Member

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    The "50" in "14-50" means 50A, so no, you can't run 80, and for a continuous load like EV charging you can only run 40 (have to decrease by 20%).

    You can plug an HPWC into a 14-50 outlet if you set the HPWC to 40A. There's some debate over whether this is to code, but the consensus seems to be that it's safe, at least. But if you want to run your HPWC at higher amperage, you need to have dedicated wiring.
     
  6. DavidB

    DavidB Aug 2013 S85

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    Are there more appliances feeding off that 80 amp breaker? If so, I'd be very concerned if they run more than 24 amps combined (excluding the Tesla).
     
  7. Sparktz

    Sparktz Member

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    Thanks for the replies guys.

    The breaker only goes to that one plug, so there is nothing else that could draw on it. The wiring is rated for 80 amps. The only hiccup is 80 amp breaker versus 50 amp breaker. Nothing else will use the plug and using the Tesla 14-50 adapter will automatically limit the pull to 40 amps (per my understanding).

    Still too risky with that additional information?
     
  8. jerry33

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

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    Yes. Totally unsafe and against code. Why not just put in an additional 50 amp breaker and run the 14-50 from there?

    The alternative is to replace the 80 amp breaker with a 50 amp one and set the dip switches on the HPWC to run at 40 amps. Then have an additional 14-50. You'd need a switch so that only one could be active at any one time.
     
  9. Nigel Tufnel

    Nigel Tufnel Member

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    I'd like to know the answer to that one as well Spartz, it seems safe to me. Of course my electrical expertise is minimal.
     
  10. green1

    green1 Active Member

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    It's not safe, because if something goes wrong and there's a short, the breaker will likely trip AFTER the outlet melts in to a pile of goop and starts a fire.

    If the wiring is truly capable of 80A then an HPWC set for an 80A circuit is a possibility, other option is to replace the breaker. There are upsides and downsides to each:
    - HPWC is expensive but faster charging
    - replacing the breaker is cheaper, but slower charging, AND there's a risk that the 80A capable wiring will physically not fit in the smaller breaker.
    Either answer would be safe and to code.

    If however the wiring matches the outlet (which is actually more likely, as the wiring for 80A is unlikely to physically fit in a 14-50 outlet) then there's only one choice, replace the breaker.
     
  11. jerry33

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

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    And bear in mind that for an HPWC to work at 80 amps, it needs a 100 amp breaker. If the breaker is 80 amps, then the HPWC needs to be set at 64 amps.
     
  12. Sparktz

    Sparktz Member

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    Thanks for all of the advice gentleman, I appreciate it!
     
  13. Cosmacelf

    Cosmacelf Active Member

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    No, not safe. Go to a home improvement store and buy a 50 amp breaker and swap it with the 80 amp one. Having said that, would I charge from it? Yeah, I would, after checking it for an hour or so to make sure it looked ok. But that's just me.
     
  14. FlatSix911

    FlatSix911 918 Hybrid

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    Sparktz,
    You have a great opportunity to install a HPWC and take advantage of the faster charging.
    Forget about down rating the breaker as you already have a dedicated circuit with properly sized wiring.
    Just install the HPWC and set the internal switches to 64A and you will get 47mph compared to 29mph with the UMC. (assuming you have on board dual chargers)

    HPWC.png
     
  15. FlasherZ

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

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    OCPD (breaker) is there to protect the conductors and receptacles from overload. This will permit a device to draw more than 50A from a receptacle rated for only a 50A intermittent load. It is dangerous - it can melt the receptacle and damage the wiring.

    This is dangerous and against code. Pop out the 80A breaker and put a 50A in it. Of all the electrical fires that I've seen, roughly a third are caused by an OCPD that was too large (penny in the fuse socket, someone who pulled a 15A breaker and replaced with 30A, etc.)
     
  16. grichard

    grichard Member De-Luxe

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    FlasherZ: Assuming that he has dual chargers, can you comment on whether it'd be sensible/safe to replace the 14-50 with a HPWC set at 80% of 80A?
     
  17. FlasherZ

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

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    Yes, if the wiring permits, that is what I would consider.
     
  18. Sparktz

    Sparktz Member

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    Thanks for the reply. Getting a Tesla certainly is improving my knowledge of electrical circuits! Can you confirm my understanding?

    If the outlet only has 40 amps drawn on it, this would not be inherently dangerous. However if the outlet somehow drew more than that, then the NEMA 14-50 might fail, long before the breaker would trip?

    Is this correct?
     
  19. Cosmacelf

    Cosmacelf Active Member

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    Correct, if there isn't a fault situation. So assuming the Tesla UMC and car work correctly, this will work fine. However, if something breaks in the car or UMC which causes it to draw much more than 40A (like a short to ground), then bad things could happen. The point of a breaker is a protection device in case things go south...
     
  20. Cosmacelf

    Cosmacelf Active Member

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    Just to give you an idea ... Once (and only once) I was diddling around in a 120V, 20A circuit box with a pair of pliers with the breaker still on. The pliers touched two wires it shouldn't have resulting in a very loud bang, a flash of light, and a tripped breaker, all in an instant. The pliers got a notch melted out of it.

    If a 2.4 kW circuit could melt my pliers in an instant, imagine what 19.2 kW 80A circuit could do, 8 times as powerful.
     

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