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3 Prong 240v plug, no neutral

Discussion in 'Model S: Battery & Charging' started by sandpiper, Jan 5, 2015.

  1. sandpiper

    sandpiper Active Member

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    Question.

    At my in laws they have a 3 prong 240vac, 50 amp rated outlet. It has L1, L2 and ground but no neutral. Rather than adding a new plug I was thinking of making a pig tail adapter to convert the 3 prong plug to the modern 4 prong, that includes the neutral.

    if I do that, of course the neutral would be unconnected. This is fine for some equipment. Is it okay for the Tesla mobile charger? Has anybody tried this? It makes sense to me that the neutral would be unused.
     
  2. Dwdnjck

    Dwdnjck Member

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    I use a 10-30 three prong dryer plug. No problems, stays cool, 22000 miles.
     
  3. RAM_Eh

    RAM_Eh Member

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    The tesla HPWC does not use the neutral. Not sure the neutral is needed at all.
     
  4. davewill

    davewill Member

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    Yes, that's fine. EV Charging only needs L1, L2, and ground. The neutral in the plug is unconnected to the EVSE. It would be prudent to label the adapter appropriately ("EV Only", or some such) since if someone were to try to use it with equipment that used the neutral, damage could result.
     
  5. sandpiper

    sandpiper Active Member

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    Outstanding. Thanks so much guys! This forum is a great resource.
     
  6. tga

    tga Active Member

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    The neutral blade on the 14-30 and 14-50 UMC adapters is unconnected.

    If their outlet is a 6-50 (L1/L2/ground), you'll have to build a pigtail adapter or find one of the rare (and getting rarer) 6-50 adapters.

    If it's a older 10-50 (L1/L2/neutral), you can build an adapter with a range cord.

    See cosmacelf's guide - http://cosmacelf.net/Home%20Made%20Adapters.pdf
     
  7. roblab

    roblab Active Member

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    You can also jumper the neutral to the ground. They are generally on the same ground bar that all the grounds and neutrals are wired to in the circuit breaker box (you should go look to prove it to yourself). So: Your 4 prong would be L1, L2, Ground, and (ground)neutral, alla same alla same.

    I am now waiting for some 50 year electrician to tell me that all these years I have been wrong and my car won't charge. I don't use an EVSE other than the outlet plug, so I can't tell if the neutral is used or not.

    BZZZzzzzt!
     
  8. linkster

    linkster Member

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    -1 (biting my tongue here so I won't be admonished by the mods (again))
     
  9. randompersonx

    randompersonx Member

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    There is no guarantee that a ground would be the same guage as the neutral would have been, and this is therefore a big risk for an electrical fire. Considering the Telsa doesn't even use the Neutral, there is no point in making a dangerous adapter cord that connects neutral to ground. Just leave the neutral disconnected and put a label on "FOR TESLA/EV USE ONLY", it's far safer.
     
  10. Doug_G

    Doug_G Lead Moderator

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    UMC is fine. Just be sure not to plug anything else into that adapter. If it expects a working neutral you could have a bit of a problem.
     
  11. TEG

    TEG TMC Moderator

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    Usually if something wants to use the Neutral too it is because it needs 120V as well as the 240V. In that case, without a Neutral, it just won't power up.
    I used a UMC with no Neutral, but some other EVSEs I have don't power up at all unless they get Neutral.
     
  12. sandpiper

    sandpiper Active Member

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    This was my concern... that something in the box needed the 120 from one phase. I didn't think it was likely because they probably sell exactly the same box to elsewhere in the world where they don't have 120 at all.

    Thanks again!
     
  13. tga

    tga Active Member

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    #13 tga, Jan 6, 2015
    Last edited: Jan 6, 2015
    Where's FlasherZ when you need him? :smile:

    No one said the car won't charge with your proposed adapter wiring. But your connection of ground to the neutral pin is completely unnecessary and exposes a potential fire danger.

    There's a good chance that 6-50 outlet was wired with 6/2 romex, with no neutral wire (6 ga romex is expensive, and 6/2 is ~33% cheaper than 6/3). A quick look at Southwire's web site (if you buy romex at a big box store, it was probably made by Southwire) shows the ground conductor in their 6/2 romex is 10 gauge: http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

    So now you've built an adapter that co-opts the ground wire into service as an undersized neutral, and allows plugging in a 50A/120V load into an outlet. The undersized "neutral" will be carrying way more current than is safe, and could easily overheat and start a fire.

    Where do you find a 120V/50A load? Beats me, but I bet Mr. Murphy can find one.

    tl;dr - Jumpering neutral to ground is unnecessary, the car doesn't need it, and is a fire risk. Don't do it.

    I guess you have more sense than me... :wink:

    Possibly. If all of the 120V loads are wired from the same hot to the non-existent neutral, then yes, it won't power up. But if the 120V loads are split between the two hots (like a big RV with a 14-50 shore power plug), things get ugly quickly, generally resulting in something going boom from voltage spikes (ie, turn on the microwave and the TV on the other hot leg fries).

    - - - Updated - - -

    The UMC doesn't need the neutral. I've charged a car with a 6/3 extension cord that does not pass the neutral (H1/H2/ground only)

    People have cut off the neutral pin of a 14-xx adapter to allow it to be plugged into any 14-xx series outlet. Obviously, this is only 100% safe if you are plugging into a higher amperage outlet (ie, a 14-30 adapter in a 14-50 outlet), and somewhat less safe if you intend to remember to dial down the current when plugging into a lower rated outlet.

    See Cosmacelf's guide, page 16: http://cosmacelf.net/Home%20Made%20Adapters.pdf where he shows cutting off the neutral pin on a 14-50 UMC adapter to plug into a 14-60 outlet.

    You should really read that guide, if you haven't already, before making any adapters. Lots of good info and safety warnings.
     
  14. linkster

    linkster Member

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    tga

    Thanks for the complete post and handling Flash's "chores" while he is on sabbatical. :wink:
     
  15. FlasherZ

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

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    No, no, no!

    This is only true in ONE panel, the service panel. All subpanels require separated ground and neutral to prevent some pretty nasty failure scenarios.

    Also, keep in mind that equipment ground conductors ("ground") are permitted to be smaller than the circuit, and frequently are bare conductors and tied to conduits and such - they are not permitted to carry current and therefore tying them together at any place other than the single service panel provides a return path for current through conduits and boxes and such.

    This should never be done!

    Your car will charge if you do this; however, just because it works does not mean it's safe. It is extremely dangerous to tie these together. If there is not a neutral available, you may not use a NEMA 10- or 14-series receptacle (which both require neutral) - you may only use a 6-series receptacle.

    (Note that the opposite -- tying ground to neutral -- was legal up to 1996 in 10-series receptacles. That's different, because the neutral is an insulated conductor rated at the circuit's size.)

    - - - Updated - - -

    This depends. In an appliance where only a single 120V load is used, then this is correct. However, if there are opposing 120V loads on different legs, this will create a problem. When neutral "floats", the two 120V loads will create a series connection between the two legs through the common floating neutral. Depending upon the current drawn by each load, you will see a voltage disparity.

    L1 ----- 120V load ----- N ----- 120V load ----- L2

    This is very typical in an RV.
     
  16. TEG

    TEG TMC Moderator

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    A storm once broke the neutral wire on the pole outside my house. Half the appliances burnt out from that. It was ugly. I could hear zapping noises all around the house. Thankfully nothing caught on fire. The power company actually reimbursed me partially for the lost equipment since the lines outside had been neglected and intertwined with tree branches that caused the problem.
     
  17. deonb

    deonb Active Member

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    Also, in Europe/Australia/South Africa this simply won't work. Neutral is commonly tied to an ELCB (think GFCI), before being tied to ground. If you have any current that's returned via a path other than neutral, it will trip the ELCB.

    I have no idea why this practice isn't followed in the U.S. Seems simpler than having GFCI's all over the place.
     

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