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Thread: Nema 10-30?

  1. #21
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    Quote Originally Posted by dhrivnak View Post
    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.
    Yes; in many, if not most home installations, a NEMA 10-30R is provided from the "service panel" (the main panel, not a sub-panel) directly where the neutral conductor is bonded to ground anyway. Even if it is provided from a sub-panel, the fact it's a 10-30R means it's likely an older system where subpanels' grounds and neutrals were permitted to be bonded per the older NEC. As a result, there is little harm or foul with connecting neutral to ground at the NEMA 14-50R end.

    Where this matters is if the NEMA 10-30R were served off a subpanel with isolated neutral and ground. For an appliance -- especially one that makes contact with earth ground, like a range sitting on concrete, for example -- this could allow stray currents from the neutral to return to ground through the chassis. It really requires another failure somewhere in the system, but I've seen enough failures to create that condition.

    Just like the NEMA 6-20 thread, do NOT do this in any permanent installation; it's a very bad idea and won't pass code. A "cheater cord" as described will work, but may have some unintended side-effects (like minor shocks in certain cases).

    - - - Updated - - -

    Quote Originally Posted by qwk View Post
    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.
    Well, you don't *need* a ground to charge. You WANT one for safety. You don't need a neutral here, because the car does not require 120V.

    We're getting mixed up on terminology. I'm using specific terminology for a reason -- safety... stick with me here as the "neutral" and "ground" are NOT interchangeable, which is why I'm making sure the caveats of this whole exercise are understood.

    The "neutral" conductor is the current return conductor for 120V needs on a center-tapped 120V split-phase system and is referenced to earth ground. The "ground" conductor is the equipment safety grounding conductor and is used to ensure there is a very low-resistance path for equipment chassis to safely return current to ground in case of a system failure.

    The "ground" conductor is for safety only and is only intended to carry current in case of a failure so that 1) humans do not become a return path to earth ground for currents, and 2) overcurrent protection devices can open in case of a short. It is absolutely required in today's world for safety reasons.

    You're correct in stating that the NEMA 14-50R will still work if the neutral pin in the receptacle is unconnected, *for charging the Tesla*. But a 14-50R is not unique to Tesla, and you must not assume others will have the knowledge that you have about that pin being unconnected. And finally, the NEMA 10-30R has no ground pin in it -- only neutral -- so tying the "ground" on one end to the "neutral" on the other is something that has to be labeled. That's why I say if you do it, 1) do it only in a cord; 2) mark that cord from here to heaven and back as I state in the preference order above. It is expected for a NEMA 14-50R to have a ground and a neutral connection. If you sell your home, or are incapacitated or die (perhaps at the hand of your own electrical invention), others must know what is present so it doesn't create a hazard.

    Electricity kills and just because it works, doesn't mean it's safe or won't burn down a building. It may seem like I'm arguing about technical details, but unfortunately I've attended the funerals of people who die from these types of mistakes.
    Last edited by FlasherZ; 2012-10-08 at 11:02 AM.

  2. #22
    4GETOIL SS70, XS4, xR913 dadaleus's Avatar
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    Seems like a non-cheater cord then would be to get a custom extension cord made with 10-30's (a P and an R) on each end and get the Tesla official 10-30 end to the charge cable. I'm assuming people wouldn't object then? (Other than objecting to using an extension in general, but I'd have it made with 6 gauge wire to make sure it has way more capacity than needed).

    I was feeling like using an adapter to a 14-50 and using that premade extension would just be nice because the extension cords are readily available and cheaper, because that would be a 6 gauge wire, and because it would be more useful if I ever needed to extend a 14-50 (not sure why I would but I always like options).

  3. #23
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    Quote Originally Posted by dadaleus View Post
    Seems like a non-cheater cord then would be to get a custom extension cord made with 10-30's (a P and an R) on each end and get the Tesla official 10-30 end to the charge cable. I'm assuming people wouldn't object then? (Other than objecting to using an extension in general, but I'd have it made with 6 gauge wire to make sure it has way more capacity than needed).
    Yes, but it obviously requires buying a 10-30P adapter, and reports are they're not ready yet. But when they are available, it is the proper thing to do.

    I was feeling like using an adapter to a 14-50 and using that premade extension would just be nice because the extension cords are readily available and cheaper, because that would be a 6 gauge wire, and because it would be more useful if I ever needed to extend a 14-50 (not sure why I would but I always like options).
    It's a good point and a reasonable strategy. At 50A, #6 copper will keep voltage drop under 2% over 100 feet and as long as you don't coil the cable, you won't have a heat problem. The reason large extensions like this are frowned upon is that repeated manipulation of the cable can cause stretching or breakage and perhaps a safety hazard. Make sure you get the right cable (e.g., rubber cord cable) for flexible use... and be sure to mark your adapter cable properly if it does something the current code doesn't expect.

  4. #24
    Model S P2681 qwk's Avatar
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    Quote Originally Posted by FlasherZ View Post
    Yes; in many, if not most home installations, a NEMA 10-30R is provided from the "service panel" (the main panel, not a sub-panel) directly where the neutral conductor is bonded to ground anyway. Even if it is provided from a sub-panel, the fact it's a 10-30R means it's likely an older system where subpanels' grounds and neutrals were permitted to be bonded per the older NEC. As a result, there is little harm or foul with connecting neutral to ground at the NEMA 14-50R end.

    Where this matters is if the NEMA 10-30R were served off a subpanel with isolated neutral and ground. For an appliance -- especially one that makes contact with earth ground, like a range sitting on concrete, for example -- this could allow stray currents from the neutral to return to ground through the chassis. It really requires another failure somewhere in the system, but I've seen enough failures to create that condition.

    Just like the NEMA 6-20 thread, do NOT do this in any permanent installation; it's a very bad idea and won't pass code. A "cheater cord" as described will work, but may have some unintended side-effects (like minor shocks in certain cases).

    - - - Updated - - -



    Well, you don't *need* a ground to charge. You WANT one for safety. You don't need a neutral here, because the car does not require 120V.

    We're getting mixed up on terminology. I'm using specific terminology for a reason -- safety... stick with me here as the "neutral" and "ground" are NOT interchangeable, which is why I'm making sure the caveats of this whole exercise are understood.

    The "neutral" conductor is the current return conductor for 120V needs on a center-tapped 120V split-phase system and is referenced to earth ground. The "ground" conductor is the equipment safety grounding conductor and is used to ensure there is a very low-resistance path for equipment chassis to safely return current to ground in case of a system failure.

    The "ground" conductor is for safety only and is only intended to carry current in case of a failure so that 1) humans do not become a return path to earth ground for currents, and 2) overcurrent protection devices can open in case of a short. It is absolutely required in today's world for safety reasons.

    You're correct in stating that the NEMA 14-50R will still work if the neutral pin in the receptacle is unconnected, *for charging the Tesla*. But a 14-50R is not unique to Tesla, and you must not assume others will have the knowledge that you have about that pin being unconnected. And finally, the NEMA 10-30R has no ground pin in it -- only neutral -- so tying the "ground" on one end to the "neutral" on the other is something that has to be labeled. That's why I say if you do it, 1) do it only in a cord; 2) mark that cord from here to heaven and back as I state in the preference order above. It is expected for a NEMA 14-50R to have a ground and a neutral connection. If you sell your home, or are incapacitated or die (perhaps at the hand of your own electrical invention), others must know what is present so it doesn't create a hazard.

    Electricity kills and just because it works, doesn't mean it's safe or won't burn down a building. It may seem like I'm arguing about technical details, but unfortunately I've attended the funerals of people who die from these types of mistakes.
    You just explained what I have posted all along, just better. Its all semantics. Aren't both the neutral and ground wires tied to the ground bar in the breaker box?

    And, yes the roadster will not charge without a ground connection, so you NEED a ground.

  5. #25
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    Quote Originally Posted by dadaleus View Post
    Seems like a non-cheater cord then would be to get a custom extension cord made with 10-30's (a P and an R) on each end and get the Tesla official 10-30 end to the charge cable. I'm assuming people wouldn't object then? (Other than objecting to using an extension in general, but I'd have it made with 6 gauge wire to make sure it has way more capacity than needed).
    Yep, that's fine - or your option of a 14-50 extension and a short adapter as you also suggested is a good solution since as you imagine a 14-50 extension cord could be more useful.

    Personally, I'm a fan of running a ground to the dryer and upgrading the receptacle/plug to a 14-30 connection. Swapping out the pigtail on the dryer is a simple thing to do if you can get a ground to your receptacle which may or may not be easy!

  6. #26
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    Quote Originally Posted by FlasherZ View Post
    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.
    There are many other threads on this forum discussing various adapters in this area... Removing the neutral from a NEMA 14-50, etc.

    Here is one that is related:
    http://www.teslamotorsclub.com/showt...ector-a-waste/
    http://www.teslamotorsclub.com/showt...ll=1#post72463
    Quote Originally Posted by smorgasbord
    ...
    Homemade NEMA 10-30 plug to NEMA 14-50 outlet
    Name:  adapt.jpg
Views: 456
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    (By the way, the old AVCON EVSE that I am using for my old EV does require both 240V and 120V, so I do need the neutral on the 14-50 for that application.)


    I think having joined neutral + ground was done in WWII and for a while after to save copper. It causes some "funky issues" with some wiring, but it did eliminate a lot of wire in old houses by joining the two functions.
    Last edited by TEG; 2012-10-08 at 12:03 PM.
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  7. #27
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    Quote Originally Posted by qwk View Post
    You just explained what I have posted all along, just better. Its all semantics. Aren't both the neutral and ground wires tied to the ground bar in the breaker box?
    True if you have only one breaker box, but not always for more complex systems. For anything in the past 20 years or so, the neutral and the ground are tied in one place only - at the service entrance (with notable exceptions like detached garages that didn't become fully isolation-required until NEC 2008). Code requires separation of neutrals and grounds, and then a bonding jumper is used to connect the neutral bar to the ground bar in the service panel. If your branch circuit for that 14-50R is fed from a sub-panel, the neutral and ground should be isolated from each other in that panel all the way back to the service entrance.

    That said, if there's a NEMA 10-30R in the home, it also likely means that the system is older than 20 years and neutral is bonded to ground in every panel, and it doesn't make all that much of a difference. But that also creates more of a chance of shock hazard or strange current return paths for a system failure, which is why it's not done anymore. As of NEC 2008, most exceptions for 3-wire service (hot-hot-neutral) have been removed and every feeder extension must be 4-wire.

    And, yes the roadster will not charge without a ground connection, so you NEED a ground.
    Thanks for confirming that. I had read that it checks for ground reference, likely for safety reasons.

  8. #28
    Senior Member strider's Avatar
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    I haven't read all the responses but since Tesla comes w/ a 10-30 adapter, don't you just need a 10-30 extension cord?

    On that stayonline.com site you can get a "custom portable outlet box" that has a male 10-30 on one end and a box on the other end w/ a female 10-30 to which you could plug in the UMC. Don't know what length you need so didn't configure one to get a price.

    That seems a lot easier than messing w/ hots, grounds, running new boxes, etc. or am I missing something?
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  9. #29
    Model S P2681 qwk's Avatar
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    Quote Originally Posted by strider View Post
    I haven't read all the responses but since Tesla comes w/ a 10-30 adapter, don't you just need a 10-30 extension cord?

    On that stayonline.com site you can get a "custom portable outlet box" that has a male 10-30 on one end and a box on the other end w/ a female 10-30 to which you could plug in the UMC. Don't know what length you need so didn't configure one to get a price.

    That seems a lot easier than messing w/ hots, grounds, running new boxes, etc. or am I missing something?
    I dont think that the 10-30 adapter is available yet.

  10. #30
    Senior Member strider's Avatar
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    Quote Originally Posted by FlasherZ View Post
    The "neutral" conductor is the current return conductor for 120V needs on a center-tapped 120V split-phase system and is referenced to earth ground. The "ground" conductor is the equipment safety grounding conductor and is used to ensure there is a very low-resistance path for equipment chassis to safely return current to ground in case of a system failure.
    This is key. The fact that a 10-30 is hot-hot-neutral is important if the device connected is going to only use one leg (120V). Many dryers use 120V to run the control panel, timers, etc. so it should stay hot-hot-neutral. However, if the device connected will only use 240V (like a Tesla UMC) then you can run a 10-30 hot-hot-ground. I am going to do this in my house as I don't have panel capacity to run a 14-50. I will label the outlet "240V EV charging only" or something. It will also help that the outlet will be in the rafters so little chance of someone plugging in a dryer
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