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Thread: Nema 10-30?

  1. #11
    Model S P2681 qwk's Avatar
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    I think you are confusing neutral with ground. While both are grounded to the breaker box, neither a 10-50 nor 10-30 have grounds, only neutrals. You could do two things that are not up to code if you have a long wire run and for whatever reason dont run a new seperate ground wire to the 14-50 or 14-30. One is leave the ground unconnected, the other is hook the ground and neutral together(not recommended). If you leave the ground not connected to anything, you just have to remember to not plug in any device that requires both a neutral and a ground, or it may cause problems.

  2. #12
    4GETOIL SS70, XS4, xR913 dadaleus's Avatar
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    Thats for the well thoughtout responses. What would be cool is an adapter that takes the 14-50 hots and neutral to the 10-30, and also has a 5-15 plug just for the ground. But sure, I could semi permanently wire in something for the ground. I just have to be able to unplug it to plug in their dryer.

  3. #13
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    Quote Originally Posted by qwk View Post
    I think you are confusing neutral with ground. [...] One is leave the ground unconnected, the other is hook the ground and neutral together(not recommended).
    Are you referring to me?

    You *never* want to leave the equipment safety ground conductor (the "ground") of a NEMA 14-series receptacle unconnected. It creates a safety hazard if one of the hot wires ever becomes broken and/or shorted to the chassis.

    The only reason that you can tie neutral and ground together when converting from a 10-30P to a 14-50R for model S is because a) NEMA 10 series applications generally expect equipment chassis ground to be done through the neutral conductor, and b) Tesla doesn't require the neutral conductor, and therefore does not use it as a current return conductor. As a result, the neutral wire can act as a safety ground in this case without too much risk. Mark the adaptor properly, ensure it's not used for anything else, and throw it away when the model S goes away. As I said, the proper way to do this is to wire a 14-50R properly, but if all you have is a NEMA 10-30, this will do and is reasonably safe for charging a model S. (I believe if you purchased a NEMA 10-30 plug for the UMC and looked at the pin-outs, you'd find they effectively do the same - car chassis to the neutral, and hot-hot to the chargers.)

    You do not want to use this cable for any other appliances, especially those that make physical electrical contact with earth ground, as it can create effectively a second neutral-ground bonding point, which is only supposed to happen at one point -- the service panel.

  4. #14
    Senior Member dhrivnak's Avatar
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    I made such a connector and have used it successfully. I needed to charge at my Son's apartment and while i have a NEMA fourteen fifty his dryer is NEMA ten thirty. I tied neutral to ground as they tie back to the same place. A trip to Lowes and less than forty five dollars i was set.

  5. #15
    Model S P2681 qwk's Avatar
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    Quote Originally Posted by FlasherZ View Post
    Are you referring to me?

    You *never* want to leave the equipment safety ground conductor (the "ground") of a NEMA 14-series receptacle unconnected. It creates a safety hazard if one of the hot wires ever becomes broken and/or shorted to the chassis.

    The only reason that you can tie neutral and ground together when converting from a 10-30P to a 14-50R for model S is because a) NEMA 10 series applications generally expect equipment chassis ground to be done through the neutral conductor, and b) Tesla doesn't require the neutral conductor, and therefore does not use it as a current return conductor. As a result, the neutral wire can act as a safety ground in this case without too much risk. Mark the adaptor properly, ensure it's not used for anything else, and throw it away when the model S goes away. As I said, the proper way to do this is to wire a 14-50R properly, but if all you have is a NEMA 10-30, this will do and is reasonably safe for charging a model S. (I believe if you purchased a NEMA 10-30 plug for the UMC and looked at the pin-outs, you'd find they effectively do the same - car chassis to the neutral, and hot-hot to the chargers.)

    You do not want to use this cable for any other appliances, especially those that make physical electrical contact with earth ground, as it can create effectively a second neutral-ground bonding point, which is only supposed to happen at one point -- the service panel.
    I think we are saying the same thing, just using different wording. The only difference I can see is on the connecting the ground to neutral which works, but isn't needed as the car just uses the neutral as ground like you mentioned.

    - - - Updated - - -

    To the OP, I think that waiting for the 10-30 adapter from Tesla is the thing to do in your case though. It's very simple, and just plugs in without much risk. All of this rewiring outlets temporarily can not only be time consuming, but you definately need a multimeter, and the necessary tools there when you attempt this.

  6. #16
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    Quote Originally Posted by qwk View Post
    I think we are saying the same thing, just using different wording. The only difference I can see is on the connecting the ground to neutral which works, but isn't needed as the car just uses the neutral as ground like you mentioned.
    Well, we want to be crystal clear here for safety, so I'm happy to clarify. You left me with the impression that you would prefer leaving the ground "unconnected" over tying the neutral and ground together in this statement:

    You could do two things that are not up to code if you have a long wire run and for whatever reason dont run a new seperate ground wire to the 14-50 or 14-30. One is leave the ground unconnected, the other is hook the ground and neutral together(not recommended).
    Leaving the "ground" pin unconnected on a NEMA 14-50R is a very, very bad idea, and I don't want to leave anyone with the impression that you should leave it unconnected. That's all. In preference order, 1) you want to run a separate ground from the NEMA 14-50R's safety ground to a safety ground conductor somewhere, so that it's unconnected to the neutral bus; 2) you connect the safety "ground" terminal on the NEMA 14-50R to the "neutral" return terminal on the NEMA 14-50R, then connect that to the NEMA 10-30P's "neutral" pin; 3) you connect the safety "ground" terminal on the NEMA 14-50R to the NEMA 10-30P's "neutral" pin and leave the 14-50R's "neutral" terminal unconnected, making sure there is PERMANENT-QUALITY MARKING that neutral is not present. There isn't a 4th option to leave the ground unconnected, it's a giant safety hazard. For #3, (the suggestion that you not connect the neutral pin on the NEMA 14-50R), see the NEMA 6-20 thread. If your cord is properly marked, it's not so much a big deal but you never want to do this on a permanently installed receptacle (it would unlikely pass inspection).

    In *most* cases, the NEMA 10-30R you plug into will be served from a run to the service panel, where neutral and ground are bonded together, and as a result in combination with the fact that the UMC doesn't require neutral, there will be no functional difference between a 10-30R and a 6-30R there.

  7. #17
    Model S P2681 qwk's Avatar
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    Quote Originally Posted by FlasherZ View Post
    Well, we want to be crystal clear here for safety, so I'm happy to clarify. You left me with the impression that you would prefer leaving the ground "unconnected" over tying the neutral and ground together in this statement:



    Leaving the "ground" pin unconnected on a NEMA 14-50R is a very, very bad idea, and I don't want to leave anyone with the impression that you should leave it unconnected. That's all. In preference order, 1) you want to run a separate ground from the NEMA 14-50R's safety ground to a safety ground conductor somewhere, so that it's unconnected to the neutral bus; 2) you connect the safety "ground" terminal on the NEMA 14-50R to the "neutral" return terminal on the NEMA 14-50R, then connect that to the NEMA 10-30P's "neutral" pin; 3) you connect the safety "ground" terminal on the NEMA 14-50R to the NEMA 10-30P's "neutral" pin and leave the 14-50R's "neutral" terminal unconnected, making sure there is PERMANENT-QUALITY MARKING that neutral is not present. There isn't a 4th option to leave the ground unconnected, it's a giant safety hazard. For #3, (the suggestion that you not connect the neutral pin on the NEMA 14-50R), see the NEMA 6-20 thread. If your cord is properly marked, it's not so much a big deal but you never want to do this on a permanently installed receptacle (it would unlikely pass inspection).

    In *most* cases, the NEMA 10-30R you plug into will be served from a run to the service panel, where neutral and ground are bonded together, and as a result in combination with the fact that the UMC doesn't require neutral, there will be no functional difference between a 10-30R and a 6-30R there.
    Can you do me a favor and just do a continuity test on a roadster UMC between the neutral and ground pin of a 14-50 adapter, and tell me how a ground that is not connected to anything helps in terms of safety?

  8. #18
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    Is one of these usable (set to some lower setting than 40A when charging?), to go from 10-30 to 14-50?
    (+Extension)

  9. #19
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    Quote Originally Posted by qwk View Post
    Can you do me a favor and just do a continuity test on a roadster UMC between the neutral and ground pin of a 14-50 adapter, and tell me how a ground that is not connected to anything helps in terms of safety?
    The continuity tester on the UMC will simply tell you that the two (neutral and ground) are not connected, and it's because the UMC doesn't need the neutral, and so it's left unconnected. That does not mean the ground pin is not needed. It's connected to the car's chassis, which is what's required for safety reasons. If you do a continuity test between the car's chassis and the ground pin on the UMC's plug when the UMC is attached, I believe you will find they are connected.

    Without that ground being present, if there is a failure of one of the hot legs and it shorts to the car's chassis, a human touching the car while standing on the earth will produce a path to ground and will get one hell of a shock. With it present, it provides enough of a path to trip the circuit breaker immediately. I believe I recall the UMC having GFCI circuitry to provide another safety here, so you have that as well.

    As a rule, equipment safety ground should ALWAYS be present, no if's, and's, or but's about it -- that's why NEMA 10 receptacles are no longer permitted for new installations post 1996 NEC.

    - - - Updated - - -

    Quote Originally Posted by ahimberg View Post
    Is one of these usable (set to some lower setting than 40A when charging?), to go from 10-30 to 14-50?


    (+Extension)
    The 30-amp connector there is a NEMA TT-30P, and is 120V. The NEMA 10-30P has an L-shaped neutral pin. I did a very quick search last night to find an RV cable to go from a NEMA 10-30P to a NEMA 14-50R for this post last night, but didn't find any in my quick search. It's likely because of the implications of its use and providing a ground.

  10. #20
    Model S P2681 qwk's Avatar
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    Quote Originally Posted by FlasherZ View Post
    The continuity tester on the UMC will simply tell you that the two (neutral and ground) are not connected, and it's because the UMC doesn't need the neutral, and so it's left unconnected. That does not mean the ground pin is not needed. It's connected to the car's chassis, which is what's required for safety reasons. If you do a continuity test between the car's chassis and the ground, I believe you will find they are connected.

    Without that ground being present, if there is a failure of one of the hot legs and it shorts to the car's chassis, a human touching the car while standing on the earth will produce a path to ground and will get one hell of a shock. With it present, it provides enough of a path to trip the circuit breaker immediately. I believe I recall the UMC having GFCI circuitry to provide another safety here, so you have that as well.

    As a rule, equipment safety ground should ALWAYS be present, no if's, and's, or but's about it -- that's why NEMA 10 receptacles are no longer permitted for new installations post 1996 NEC.
    Ok, so I dont even know what you are arguing about here. Of course you need a ground to charge(whether you call it neutral or ground), but having both the neutral and ground grounded is not necessary, and can be detrimental to other devices that are plugged in to the outlet. In fact, connecting them together on a outlet receptacle is more risky than just having one not connected. In the case of the roadster, having both connected is in fact the same as having only one connected as it only uses one to charge(as verified by the continuity test). Connecting both would accomplish exactly nothing.

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