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Thread: How to make a 30 amp J1772 extension cord for public charging

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    How to make a 30 amp J1772 extension cord for public charging

    Link to Nissan LEAF forum thread on the same topic:
    My Nissan Leaf Forum View topic - Need a circuit designed to limit charge to XX amps max


    I'm sure there are folks who would like a J1772 extension cord without all the expense of another EVSE. This will work great in public charge station spots that are blocked by another car, but you could use that charge station if you could just add 25 feet more to the plug!! 30 amps maximum on this one, which is what virtually all public J1772 charge stations are:






    DRAFT 2:

    Last edited by TonyWilliams; 2013-09-27 at 09:34 AM.

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    The only thing to note is that you violate NEC 625 when you use a J1772 extension cord. Should your car burn up while it is being used, you may not be able to recover based on an insurance claim. There is a gray-area argument that you could use here - that EVSE equipment is an appliance and isn't subject to NEC oversight, but the insurance company has the money and you'd be out while trying to prove your case.

    Quote Originally Posted by NEC 625.17
    "The overall length of the cable shall not exceed 7.5 m (25 ft) unless equipped with a cable management system that is listed as suitable for the purpose."
    - - - Updated - - -

    Full disclosure: I do use the occasional extension cord which violates 625.22 (mostly my 14-50 extension cord). I accept the risks occasionally, just be sure you are knowingly accepting the risk as well.

    Quote Originally Posted by NEC 625.22
    "Where cord-and-plug-connected electric vehicle supply equipment is used, the interrupting device of a listed personnel protection system shall be provided and shall be an integral part of the attachment plug or shall be located in the power supply cable not more than 300 mm (12 in.) from the attachment plug."

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    Senior Member hcsharp's Avatar
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    Quote Originally Posted by FlasherZ View Post
    The only thing to note is that you violate NEC 625 when you use a J1772 extension cord. Should your car burn up while it is being used, you may not be able to recover based on an insurance claim. There is a gray-area argument that you could use here - that EVSE equipment is an appliance and isn't subject to NEC oversight, but the insurance company has the money and you'd be out while trying to prove your case.



    - - - Updated - - -

    Full disclosure: I do use the occasional extension cord which violates 625.22 (mostly my 14-50 extension cord). I accept the risks occasionally, just be sure you are knowingly accepting the risk as well.
    FlasherZ, do you see any obvious risks from using an extension cord like Tony has designed? I've thought about it but can't think of any. Not that you would necessarily be aware of an increased risk, but wondering if anything pops out at you.

    Also, I didn't know that using a NEMA 14-50 extension cord created a violation. Lots of companies make these extension cords for RVs and some are UL approved. I always assumed the NEC and J1772 prohibition against extension cords only applied to extensions to the J1772 cable like Tony proposed above, and that the EVSE started at the receptacle on the end of the extension cord. NEC 625.22 only states that the cord needs to have a listed system of protection against electric shock. Would your extension cord be in compliance if it had an interrupting protection device within 12 in of the attachment plug? Thanks for your insight.

    @Tony, one other thing you might want to mention is that most J1772 inlets come with a 2.7k resistor installed between the proximity pin and ground. Many vehicles will not charge unless you remove that resistor from the extension cord inlet.

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    Quote Originally Posted by hcsharp View Post
    FlasherZ, do you see any obvious risks from using an extension cord like Tony has designed? I've thought about it but can't think of any. Not that you would necessarily be aware of an increased risk, but wondering if anything pops out at you.
    Not for reasonable lengths as long as obvious precautions are observed. Don't throw the extension coupling in a lake along a dock.

    Also, I didn't know that using a NEMA 14-50 extension cord created a violation. Lots of companies make these extension cords for RVs and some are UL approved. I always assumed the NEC and J1772 prohibition against extension cords only applied to extensions to the J1772 cable like Tony proposed above, and that the EVSE started at the receptacle on the end of the extension cord. NEC 625.22 only states that the cord needs to have a listed system of protection against electric shock. Would your extension cord be in compliance if it had an interrupting protection device within 12 in of the attachment plug? Thanks for your insight.
    This is a gray area, one could argue EVSE equipment is an appliance and doesn't get covered by NEC anyway. That would be played out in court but while that is happening you'd likely be on the losing end (i.e., insurance company wouldn't pay until the court forced them to after you fought it). The intention of 6.22 is to provide GFCI within 12" of the receptacle to prevent shocks, and to keep the constantly-energized portion as short as possible, and to keep the greatest amount subject to the car's secure coupling. If you had a GFCI function on the head of the extension cord, that would work as well.

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    Quote Originally Posted by FlasherZ View Post
    This is a gray area, one could argue EVSE equipment is an appliance and doesn't get covered by NEC anyway. That would be played out in court but while that is happening you'd likely be on the losing end (i.e., insurance company wouldn't pay until the court forced them to after you fought it). ...
    They must have felt like the appliance was the car, and the EVSE was part of the electrical system that supplies the car. So are you suggesting that most of the several pages that constitute NEC 625 are based on an assumption by the NFPA that an EVSE is not an appliance and therefore they can write codes about it?

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    What happens if you plug this into a 70A EVSE? Does the pilot signal get passed through unaltered, allowing the car to pull more than 30A? That would be bad.
    Last edited by markb1; 2013-09-20 at 05:07 PM.
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    Quote Originally Posted by markb1 View Post
    What happens if you plug this into a 70A EVSE? Does the pilot signal get passed through unaltered, allowing the car to pull more than 30A? That would be bad.
    The pilot signal is unaltered in Tony's design. He specified a 30A cable however. If you use it at 70A then you will need a 70A cable, J1772 inlet and connector. Not sure if Leviton is still selling their 70A cable set but other vendors have them.

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    Quote Originally Posted by hcsharp View Post
    The pilot signal is unaltered in Tony's design. He specified a 30A cable however. If you use it at 70A then you will need a 70A cable, J1772 inlet and connector. Not sure if Leviton is still selling their 70A cable set but other vendors have them.
    So, that's potentially dangerous to build this for anything less that the maximum J1772 current, which I think is at least 80A. Building it for less current means you always have to remember to make sure the car doesn't draw more than the extension is designed for. A better design would be to alter the pilot signal to prevent any user error.
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    Quote Originally Posted by markb1 View Post
    So, that's potentially dangerous to build this for anything less that the maximum J1772 current, which I think is at least 80A. Building it for less current means you always have to remember to make sure the car doesn't draw more than the extension is designed for. A better design would be to alter the pilot signal to prevent any user error.
    I appreciate everybody's critiques. First, let me offer that no extension cord that I'm aware of passes a "max amperage command", which means that the guys who are using a NEMA 14-50 extension cord can obviously overload it on EVSEs and chargers that can pull more than the rated amount.

    I find that this J1772 extension, as opposed to a generic extension cord, offers increased safety. The GCFI still operates, and all the other safety protocols of J1772. Extension cords do not. The issues with maximum current over 30 amps is easily rectified with an 80 amp rated cable and J1772 inlet and plug (none of which exist anywhere on the planet that I'm aware of). Alternately, the 30 amp cable could continue to be used safely on public 30 amp charge stations only (which was the impetus).

    The 14-50 extension cord offers no protections for a disconnect under load, possibly causing a spark / fire; this J1772 extension does integrate the 100ms disconnect at both ends. A NEMA 14-50 extension cord "dropped in water" could suffer the same fate as this J1772 extension. But, the J1772 extension would use the GCFI of the EVSE to protect it; the extension cord, once again, does not protection.

    Good point on the 2.7k resistor on the J1772 inlet. The ones I have do not include this, but it's reasonable to expect that some/many would. Yes, it would also need to be removed in addition to the 150 ohm resistor in the plug.

    As to NEC, UL, laws, rules, regulations, insurance, et al, they are different all over the world, and I make no attempt to address them. Safety is paramount. Caveat emptor. No warranty for merchantability. Offered as-is, with all faults.

    Could a circuit be added to limit this extension to only the max rating of the cable? Of course. The simple logic would need:

    1) pilot signal duty cycle at 30 amps or less, no change.

    2) pilot signal duty cycle over 30 amps, change output duty cycle to 30 amps
    Last edited by TonyWilliams; 2013-09-21 at 06:33 PM.

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    Quote Originally Posted by TonyWilliams View Post
    I appreciate everybody's critiques. First, let me offer that no extension cord that I'm aware of passes a "max amperage command", which means that the guys who are using a NEMA 14-50 extension cord can obviously overload it on EVSEs and chargers that can pull more than the rated amount.

    I find that this J1772 extension, as opposed to a generic extension cord, offers increased safety. The GCFI still operates, and all the other safety protocols of J1772. Extension cords do not. The issues with maximum current over 30 amps is easily rectified with an 80 amp rated cable and J1772 inlet and plug (none of which exist anywhere on the planet that I'm aware of). Alternately, the 30 amp cable could continue to be used safely on public 30 amp charge stations only (which was the impetus).
    I agree but public and fixed charging stations don't really give you the option of using a generic extension cord. The safety issue boils down to the same arguments against using other extension cords - it's too easy to undersize the cord/plug/receptacle. I think yours is safer for the reasons you mentioned and because very few public stations are more than 30A. And you specified a thermal protection switch, although marked optional. The only exception is in Europe where most charging stations don't have cords. You have to bring your own. There is a standardized system using passive components in the cord that allows the charging station to determine the capacity of your cable.

    It's also possible to buy 80A EVSE cable here, made in USA, although it probably won't be for sale much longer. ITT-Cannon has a 75A J1772 coupler with 75A cable, and a couple of other sources have couplers rated at 70A to use with a cable like that linked above.

    I have to confess if I was doing this I would be very tempted to build a 30A cable like you did. I can't imagine using it anywhere that has more than 30A.

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