Ok to pair lower amp EVSE with 50 amp breaker?

Discussion in 'General' started by ihaveanemu, Oct 20, 2019.

  1. ihaveanemu

    ihaveanemu New Member

    Sorry if this has been asked before and it may be common sense for those of you with electrical experience, but it’s the opposite problem that most articles & threads have discussed so wanted to confirm.

    I had an electrician come in and he installed a 50 amp circuit, breaker and a NEMA 6-50 receptacle in anticipation of getting a plug in hybrid. I recently purchased a 30 amp max plug-in EVSE that asks for a 40 amp breaker. In my mind I always thought it would be okay to have the EVSE under the breaker amperage, just not over. Am I good to utilize the 30 amp EVSE and 50 amp breaker?
     
  2. bwilson4web

    bwilson4web Well-Known Member

    Yes. Amps used should always be equal to or less than 80% of the breaker rating.

    Bob Wilson
     
  3. David Green

    David Green Well-Known Member

    Bob's answer is correct in one area (80% for continuous loads) but wrong in the general larger breaker size is ok... Many electrical devices are rated for minimum and maximum breaker sizes. Minimum breaker size is to avoid nuisance trips, and supply the needed current. Maximum is often also regulated for fire safety as they want the breaker to trip before burning up the weakest link in their device (usually the cord). Usually a 30AMP EVSE should be fused at 40AMP. I never recommend going with bigger is better philosophy as the breaker is the safety device in the loop. If you want to upsize the wire that is great as it will operate cooler, and give you some level of future proofing. I always use 6 gauge copper on a "GFCI breaker" if the EVSE is in the garage (code change in the 2017 NEC code). This is an often misunderstood section in the code because the wording is horrible, but we requested an explanation from NEC on this to confirm.
     
    R P likes this.
  4. gooki

    gooki Active Member

    It's fine.
     
  5. David Green

    David Green Well-Known Member


    Its fine? Will you be in line for liability if something goes wrong? NEC allows the 50 Amp breaker on that plug type, but that device manufacture may not certify their device with a 50 amp breaker.
     
  6. gooki

    gooki Active Member

    It's fine to use a device with a power draw lower than the breaker limit.

    Do you worry about plugging in your 0.5 amp cellphone charger in your 10 amp socket?
     
    NeilBlanchard likes this.
  7. David Green

    David Green Well-Known Member

    Not sure where you are, but here in the USA most residential circuits are 120V 15 AMP / 20 AMP, but your cell phone charger has a transformer that plugs directly into the outlet and drops the voltage and current
     
  8. eneka

    eneka Member

    It shouldn't be of any issue, but if you wanted, you could swap out the breaker to a 40amp one
     
  9. BlueKonaEV

    BlueKonaEV Well-Known Member

    I run a 40 amp breaker for my 32 amp EVSE even though the manual of the EVSE calls for a 50 amp breaker. I can always change the breaker if it trips.
    Theoretically, I believe that a 50 amp outlet (NEMA 6-50 or 14-50 (which I have)) should have a 50 amp breaker and it can be used for other devices that draw up to 50 amps. If I would sell the house, I would change my 40 amp breaker to a 50 amp breaker for the breaker to match the rating of the outlet as it is possible that it would fail a potential home inspection.
     
  10. David Green

    David Green Well-Known Member


    Breaker should be sized for the load always, and a home inspector should not call out a 40 Amp breaker driving a NEMA 6-50 or 14-50 as that is not a violation of code, those outlets are typically rated for a "maximum" of 250V and 50 Amp.

    If your EVSE calls for a 50 amp breaker, its fine to run a 50 AMP breaker regardless of the EVSE current as that means the device has been tested and approved on 50 AMP circuits, In that case, I would only run a 40 AMP breaker to protect 8ga copper wire if that is what you ran? Most electricians often try to run the cheapest wire possible to do the job (I never understood this mentality) and I have even seen some aluminum wire on car charger installations. That is really lame and goes back to the electricians understanding of continuous load circuits. On car charger circuits the wire gets pretty warm, and if in the summer time with a hot ambient weather you can reach the tested limits of the wire insulation. I finally trained the electrician that wires the homes I build to run conduit and pull single THHN wires for our car chargers, it costs a bit more than romex, but the wire has better insulation. For me the biggest reason is this way you are 100% future proofed if you need to pull larger wire later (car chargers get more powerful).
     
  11. bwilson4web

    bwilson4web Well-Known Member

    You might check the wire gauge from breaker box to outlet.

    Bob Wilson
     
  12. BlueKonaEV

    BlueKonaEV Well-Known Member

    I did run #8 wire as it's more than sufficient for a 32 amp EVSE. #8 is good to 50 amp peak but not for 50 amp continuous load.
    #8 would actually still be ok for an 40 amp EVSE (40 amp + 20% = 48 amp.. 48 amp < 50 amp) even though #6 would be a better choice for a 40 amp EVSE.
     
    bwilson4web likes this.
  13. David Green

    David Green Well-Known Member

     
  14. David Green

    David Green Well-Known Member


    Wow, you have installed, and suggested a system with zero margin for error, and forgot to de-rate for summer temperatures. The NEC has a de-rate schedule by ambient temperature, and NM-B (Romex) has a very low 60C temp rating. I would not install what you are suggesting at a 40 continuous load. I am to saying it will not work, or you will not get away with it, but why build a system with such little redundancy?
     
  15. BlueKonaEV

    BlueKonaEV Well-Known Member

    There would be no point of even going to a 40 AMP EVSE as my Kona only has a 7.2 kwh onboard charger, so it can't take anything over 32 amps anyways. Unless I would get a different EV that can pull more amps, there is no need for me to upgrade.
     
  16. David Green

    David Green Well-Known Member

    I see, Ya, my E-Tron is charging at 39.4 to 39.9 Amps typically, and all of the equipment generates some heat including the EVSE connected to the car. It is well below the max allowed temps, but I prefer to be safe rather than push the edge of the envelope on all the charging equipment.
     
  17. BlueKonaEV

    BlueKonaEV Well-Known Member

    If I'd upgrade to a 40 amp EVSE, I would go with #4 wire.. There really isn't a huge difference between #8 and #6.. Once you get to #4, there's quite a difference on what kind of amps that they can handle..
     
  18. R P

    R P Well-Known Member

    #6 is hard enough to work with (very stiff) compared to #8. #4 would be that much harder. I know, because I did my 14-50 receptacle with #6, but use a 40 amp breaker for my 32A EVSE. However, it is now future proofed for a 50A breaker if I ever get a 40 amp EVSE.
     
  19. apu

    apu Active Member

    In regards to folks trying to protect the weakest link with service breakers you have to remember a service breaker's job is solely to protect the house wiring not any end appliances or evse. A properly designed and constructed evse will have its own over current protection.
     
    KENNY likes this.

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