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Nema 14-50 120V reading?

Discussion in 'Model S: Battery & Charging' started by Ghosty, Sep 22, 2017.

  1. Ghosty

    Ghosty Member

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    Licensed electrician came to my place and installed a Nema 14-50 outlet. When completed, he showed me the digital meter showing 120V. After he departed, I realized it should be reading 240V not 120V.

    However, I came across a video that partially showed a meter reader and I thought I saw it as 120V as well. So I figure maybe its because each Hot is 120 for a total of 240?

    So if you test One Hot with Neutral or Ground it will show 120V. If you test both Hots at the same time - it will show 240V?
     
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  2. Lloyd

    Lloyd Well-Known Member

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    This is correct
     
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  3. KarenRei

    KarenRei KarenRei KarenRei KarenRei KarenRei KarenRei

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    Yep, split phase. Lines from the transformer come from both ends as well as the middle, with the middle as the neutral. ~120V between the neutral and either phase, ~240V between the phases.
     
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  4. Ghosty

    Ghosty Member

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    And off I go - leave office today - flying in to SF tomorrow and I should be back in Las Vegas with my Tesla! So excited! Thanks for the confirmation on the Nema 14-50. I'm all set!!
     
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  5. Bebop

    Bebop Member

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    Is it normal to show about 249-250 volts? I’m wondering why everyone seems to be getting 240V exactly checking with a multimeter.
     
  6. Barry

    Barry Active Member

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    That's within accepted range. Generally it's 240 (or 120) +/- 5%. It should drop a few V when you're plugged and charging.
     
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  7. animorph

    animorph Member

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    I frequently hit 250V charging after midnight. You might notice the current might not hit maximum in that case. It's been a while since I checked, but I think I get 70A or 71A instead of my 72A max when the voltage is that high. It's probably power limiting as well as current limiting.
     
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  8. dhanson865

    dhanson865 Active Member

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    No, 250V is a bit high. Not a problem but not "normal" either.

    If you gave me a choice between 240V or 250V I'd prefer 250V though. It's better for efficiency on most devices and in the case of an EV it'll charge faster.

    ANSI C84.1 Service Voltage Limits

    Ø Range A minimum voltage is 95% of nominal voltage
    Ø Range A maximum voltage is 105% of nominal voltage

    240V is nominal in this case and 105% of 240v is 252V so you are inside the acceptable range just not centered on it.

    Call it "normal' or "high", it's still good.
     
  9. brucet999

    brucet999 Active Member

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    If by that you mean touching your voltmeter probes to the two hot terminals, yes. You would be reading the potential between the two hot leads.
     
  10. rhumbliner

    rhumbliner Member

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    Just curious, why are you taking delivery in SF instead of Vegas?
     
  11. Ghosty

    Ghosty Member

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    I purchased car from private party in Bay Area. Entire transaction was done in CA. No tax for me, since NV does not collect a tax on private party sales. No Tax in CA b/c not registering car in CA. =)
     
  12. wwu123

    wwu123 Member

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    I get about 248-250V as shown on my utility's smartmeter, or testing at the outlet with a multimeter. But that's with no heavy load. Once I start charging the car, according to Teslafi, the car sees only 246V, dropping after 30 minutes to 242V or so for most of the charge. I'm not sure where the car is measuring the voltage, whether at the outlet, the charge port, or the battery - but some of the voltage drop is resistance in the house wiring, and some in resistantce in the UMC that heats up quite noticeably.

    Congrats OP on the new car!
     
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  13. rhumbliner

    rhumbliner Member

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    Brilliant! :)
     
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  14. FlyingCookie

    FlyingCookie Member

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    Seeing 250 at night isn't terribly unusual, as there's a lower load on the grid and that causes slightly higher voltage. (In most places)

    250 is perfectly fine for most anything designed for 240... Seeing 250 at night is much better than seeing 215 during the day when everyone has their A/C running, which in some places is the other option. :)

    I often see as high as 257 before I start charging at night at my friend's house in Central Mississippi. He lives in a neighborhood that basically has a universal bedtime of 10:30, so by 11:00, when i'm usually rolling in, there's basically no load on the grid in the area due to low demand. (And no time of use billing, so no one really cares when they use power) During the day, though, it may fall as low as 237 before I start charging.
     
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  15. Barry

    Barry Active Member

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    That should be reported to the power company because it's out of spec. It will cause premature failure of many electric appliances because that's 128.5V.

    I had a high voltage issue a number of years ago when I lived in PA. After PECO fixed it, they reimbursed me for some things that blew (big one was an oven heater element).
     
  16. FlyingCookie

    FlyingCookie Member

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    Yeah, but it makes my hair dryer hotter! :D

    I'm sure the problem has been reported by other people, but due to the wide fluctuations, I think Entergy would rather pay for the random dead appliance than for the infrastructure to truly fix the problem. That whole area swings from high to low, and has for probably the last five years now. I remember sticking a meter in the wall one morning and finding 108 volts and then later that night finding 126 in a neighborhood near my friend's house.

    Somewhat ironically, he did recently have the bake element in his oven fail...
     
  17. Barry

    Barry Active Member

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    If a complaint is filed with the state PUC, they won't have a choice. Specs are there to be followed. If it swings all over the place, their design is faulty and needs to be fixed. Utilities don't like to have regulatory agencies up their butt, either.
     
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