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NEMA 14-50 AMP?

Discussion in 'Model S: Battery & Charging' started by Jason Shelton, Jun 8, 2016.

  1. Jason Shelton

    Jason Shelton Member

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    I've been researching and couldn't find any answers about my specific question. Is NEMA 14-50 limited to 40 amps? Or no? My Tesla is the updated model so I have the 48 AMP charging. Will a NEMA 14-50 be able to charge at 48 amps? Or is it limited to 40 amps? If it is limited to 40 amps will I have to purchase the HPWC to get the full 48 amps? Thanks!
     
  2. Max*

    Max* Autopilot != Autonomous

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    The NEMA 14-50 is meant to supply 50A max. But if you're using a continuous load, like an EV charging, it can only do 40A max (and the Tesla won't let you go above 40a in the car). So yes, if you want 48A, you need a HPWC with a 60A breaker.
     
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  3. rhumbliner

    rhumbliner Member

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    For continuous duty you must reduce your amperage to 80% of rated capacity which means 40 amps in this case. The Tesla supplied 14-50 adapter will do that for you. This topic is covered all over these forums. Search especially for posts by @FlasherZ and @Ingineer for more detailed info.
     
  4. MorrisonHiker

    MorrisonHiker S 90D 17.17.4

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    Yes
    No
    Yes
    Yes
     
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  5. linkster

    linkster Member

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    Doubtful you'll need the extra 8 amps. Several forum members actually turn down their 14-50s so that the UMC runs cooler. Approximately 3.5 years/60,000+ miles here with 80 and 160-mile commutes deploying "only" a 14-30 (24A).

    Good-Luck!
     
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  6. FlasherZ

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

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    Not only will you need an HPWC (or another EVSE rated to charge at 48A), but it will need to be on a 60A circuit, not a 50A circuit. Charging loads (see NEC art 625) are considered "continuous loads", and that means that all equipment (conductors, breakers, receptacles, boxes, etc.) need to be rated at 125% of that load.
     
  7. Jason Shelton

    Jason Shelton Member

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    Thanks everyone! I'll just stick to the NEMA 14-50. It'll serve me right. Thanks!
     
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  8. travwill

    travwill Active Member

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    All good advice. Just remember you really never want to exceed 80% of a rated amp breaker/wires with a continuous load - they will overheat/melt/etc in time. Simple calc.
     
  9. LHendren

    LHendren Supporting Member

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    An electrician installed a NEMA 14-50 outlet for me last week. On the first day (50% initial charge), the Tesla app showed 27 mi/hr; 240 v and 40/40 A. Every day since the installation, the Tesla app shows 19 to 20 mi/hr, 224 v and 30/40 A. I don't understand what is occurring to describe to the electrician. TIA.
     
  10. TexasEV

    TexasEV Active Member

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    When the car senses a voltage drop it reduces charging amps from 40 to 30. It then remembers that limit for the next time you charge. You need to manually set it back to 40A and try again. If it drops to 30A again, tell your electrician the car is sending a voltage drop somewhere. It could be the new outlet, or anywhere from the transformer to the outlet.
     
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  11. Saghost

    Saghost Active Member

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    224V. That's why.

    Tesla has protection built in to the car - when it senses a large voltage drop, it decreases the current draw to prevent a fire. Going from 240V to 224V is tripping those protections, which is why it set the charge rate down to 30A.

    (It'll stay low for that location after it drops for an event, even if the event is transient and the voltage goes back up. If you're certain it's safe, you can turn the amperage back up and it'll stay high until another voltage drop happens.)

    The big question is why there's so much resistance. A loose connection on one of the wires on one end? Damage in the plug? Something else drawing a lot of power from your line (HVAC?) - but if you're consistently seeing 224V at the car, if it's another load that other load must be on each of the time's you've looked at it.
     
  12. gregd

    gregd Member

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    224v is really low for a nominal 240 volt feed, but we have seen posts here by others where that was what the neighborhood experienced. So, in their case, it wasn't a faulty installation, but rather a result of a weak infrastructure. But, it needs to be checked out to be sure that's what is going on.

    What I would do is find another plug in the house and measure the voltage there before and during the car's charging. If the plug is a 120v variety, double what you measure. If you don't have a meter, just use an old-style (incandescent!) lamp. If the car's charging causes a similar drop in voltage (or dimming of the lamp) on that plug, the problem is outside of your house. Call the Electric company.

    If the other outlet stays pretty stable, but the car still dips to 224v, call your electrician before serious damage is done.
     
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  13. LHendren

    LHendren Supporting Member

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    Okay - further testing this morning:
    Detached garage with new line running approximately 80 feet from house.

    Not charging - Inside house voltage is 240.6 (120.3 x 2); Garage voltage at 120 outlet is 242.2 (121.1 x 2)
    Charging - Inside house voltage is 236.6 (118.3 x 2); Garage voltage at 120 outlet is 236.2 (118.1 x 2)
    Tesla app shows 19mi/hr; 231 volts; 30/40A

    Thanks again for everyone's help.
     
  14. Rocky_H

    Rocky_H Active Member

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    Hmm, I would lean toward your charging circuit having the issue. 120 to 118 in the house is close to in the noise, and a heavy load can drag down the overall house feed by a couple of volts sometimes. For the charging circuit to be an additional 5V lower than that with the charging level already reduced to 30 out of 40 amps, that's not too good. On mine, from the car's reading, it goes about 3V lower when charging than without.
     
  15. Lloyd

    Lloyd Supporting Member

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    Something is turning on to limit your charging. 236 v is fine. 224 is too low while charging. Have your wiring checked and figure out where the drop is occurring.
     
  16. rypalmer

    rypalmer Member

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    In Canada, it's limited to 32 amps, since most NEMA 14-50's are on 40 amp breakers AFAIK.
     

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