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Help: 50amp 240v limiting to 32 amp only

Discussion in 'Model 3: Battery & Charging' started by JoganJani, Jul 26, 2018.

  1. JoganJani

    JoganJani Member

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    I just got a 50 amp breaker in my sub panel to feed by 8 gauge wires to Nema 14-50 installed. When I charge with the supplied mobile adapter I can see it draws only 32 amp. I was thinking it will draw 40 amp. I cannot up the amperage on the screen either. Any reasons you guys can think of?
     
  2. Zaxxon

    Zaxxon Supporting Member

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    The gen 2 UMC is a 32A EVSE. Your observation is normal.
     
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  3. JoganJani

    JoganJani Member

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    Wow! I didn't know that. So only to get more amperage or more mi/hr is using a wall connector?
     
  4. Zaxxon

    Zaxxon Supporting Member

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    Or another EVSE like a JuiceBox, yes. Or buy someone's gen 1 UMC.
     
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  5. TexasEV

    TexasEV Well-Known Member

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    If you read the home charging section of Tesla’s web site the options and the amps for each are explained clearly.
    Home Charging Installation
     
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  6. JoganJani

    JoganJani Member

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    Why would they do that though? ANy specific reason they changed it for Gen 2?
     
  7. tpham07

    tpham07 Active Member

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    For one, in Canada they can only draw 32A max. Another, too many NEMA 14-50s are installed on 40A circuit breakers. Thirdly, early models of Gen1 chargers melted plugs and outlets when drawing full power.

    32A is listed in the owners manual and most likely on the charger unit itself. https://www.tesla.com/sites/default/files/downloads/gen_2_mobile_connector_owners_manual_32_amp_en_US.pdf
     
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  8. JoganJani

    JoganJani Member

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    Thanks Guys. I better RTFM :p
     
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  9. eprosenx

    eprosenx Active Member

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    I suspect that moving from 40a down to 32a also allowed them to make the UMC Gen 2 slightly smaller/lighter and probably cheaper than the old UMC Gen 1. As others mentioned, it seems to have added a margin of safety for electrical jobs that were not up to snuff. It is generally legal to have a NEMA 14-50 receptacle on a 40a branch circuit. The highest current "continuous load" allowed on a 40a circuit is 32a. All EVSE's are considered "continuous loads". While what should happen is a breaker should blow if things go wrong, but there is always the chance that something goes wrong and it causes a fire instead.

    Note that I think they still sell a version of the UMC Gen 1 that has a fixed pigtail Model S/X Corded Mobile Connector I don't see it documented anywhere, but I suspect this can still do 40 amps.

    But yeah, if you want more than what the UMC Gen 2 will do, I would probably just install a wall connector. That is what I did.
     
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  10. TexasEV

    TexasEV Well-Known Member

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    I was going to say that, but I already told two posters today to RTFM in response to other questions and it’s getting kind if tiring to keep repeating that.
    But really, new owners NEED TO RTFM. This is unlike any other car you have ever owned.
     
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  11. eprosenx

    eprosenx Active Member

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    Also: What kind of wire was used? If it was NM wire (Romex) then this is not a compliant installation. You have to use the 60c rating with NM cable which would only allow 8awg to handle 40 amps (32 amps continuous). If using THHN in conduit (as an example) then 8 AWG is good for 50 amps (40 amps continuous).
     
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  12. Rocky_H

    Rocky_H Active Member

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    Yes, the corded mobile connector does supply 40A, so it could handle this. But really, if you're going to buy an extra something, I would instead just get a wall connector for about the same price.
     
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  13. Rocky_H

    Rocky_H Active Member

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    I walk on eggshells around here, because the uptight moderators smack people down way too easily, but I really respect your willingness to tell people to RTFM.
     
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  14. JoganJani

    JoganJani Member

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    I am iusin THHN #8 hence i was surprised not setting 40 amp. Now i know it's restricted on UMC side.
     
  15. aronth5

    aronth5 Long Time Follower

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    TexasEV is absolutely correct in pointing the need to RTFM. I took his advice awhile back and was not at all surprised when my 14-50 on a new 50 amp breaker only drew 32 amps.
    You will find an awful lot of advice on these forums that is not correct.

    For anything electrical this is a good source of information.
    FAQ: Home Tesla charging infrastructure Q&A
     

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