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How to build a 30 Amp Extension Cord for 24 A, 240 V charging

Discussion in 'Charging Standards and Infrastructure' started by GSP, Aug 25, 2016.

  1. GSP

    GSP Member

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    I plan to make a 30A extension cord for temporary charging at vacation rentals. I most likely will go with 50 foot length, but I may need 75 or 100 feet. On one end I will use an L6-30P, and I will make adapters for the various 30 and 50 Amp outlets to an L6-30R. On the other end I will use a 14-30R. I am counting on getting a 14-30 UMC adapter from Tesla so that I can be assured that charging will always be limited to 24 Amps (Max for a 30 A circuit).

    Reading an ampacity chart I found on the Internet, it looks like 10/3 SOOW cable is rated for 30 Amps for up to 50 foot lengths. I think this cable has three 10 gauge conductors, for the two hots and a ground.

    I am looking for advice on the type of cable to buy, and the overall setup. Is the 30 A cable rating for the circuit breaker, and therefore this is the correct size for 24 A continuous loads? Is there a better/lighter/less expensive cable that I could use, perhaps with a smaller ground wire?

    For people who have done this already, is 50' long enough for most places you have visited? If you need more that 50' is it necessary to step up to heavier, more expensive 8/3 cable?

    Thanks,

    GSP
     
  2. linkster

    linkster Member

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    #2 linkster, Aug 25, 2016
    Last edited: Aug 25, 2016
    I find myself rarely using my medium duty self-limiting charging kit #2 (L6-30 10ga) these days for two reasons, The first is, my QCP stretched 50' UMC usually reaches most friends/relatives dryer outlets and the second reason is that I like my lightweight kit #1 which uses a much lighter 12ga. extension cord that safely self-limits to [email protected] I purchase ready made L6-30 extension cords with machine crimped, molded ends on Amazon in various lengths. If i find that my car is upset with the voltage drop (due to many variables) I just reduce the amps a bit. I tend to plan a bit excessive, so I may carry a 100' extension on certain occasions.

    It can be dangerous to use extension cords for charging which is why it is always best to follow Tesla's guidelines to never use them.
     
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  3. GSP

    GSP Member

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    Linkster,

    Thanks for the info. I like the idea of getting the UMC stretch better than using extension cords.

    For occasions where the 50' UMC do you have more info on your lightweight kit #1 that you would share? Does it use L6-30 connectors with 12 gauge, or did you mean L6-20?

    I already have a 12 gauge 100' extension cord that I have used with my Volt for 120 V charging. Could it be repurposed as a 240 V cord if the insulation rating is over 250 V?

    Thanks again,

    GSP
     
  4. linkster

    linkster Member

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    I purchased both EVSEadapters.com 10-30P->L6-30R and 14-XXP->L6-30R adapters. I cut off the L6-30R ends and re-wired both with [email protected] by using L1, L2, + grnd. Both of these adapters are well labeled "WARNING 240V" and "TESLA CHARGING ONLY" with red electrical tape. Both QCP and EVSE will custom make these adapters for you including a 6-20P->[email protected] I use an unmodified 5-20 terminated 12ga. 50' extension (Amazon) or an unmodified 5-20 terminated 10ga. 100' (Home Depot) with a Tesla UMC 5-20 adapter that self-limits to [email protected] for 11-12 mph charge rate. I also use both of these off-the-self extension cords for charging on microwave and washing machine 20A 120V circuits for ~5mph charge rate if I have verified they are wired to properly carry a 20A load. I always check all connections at 15min, 30min, and 2hrs for excessive heat after charging starts to help insure a safe charging session and I learned (from @Cottonwood) to always spread out the extension cords and never leave them tightly coiled which can trap heat.
     
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  5. GSP

    GSP Member

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    Thanks for the additional info. It is very helpful.

    Based on your experience, I probably will not bother making a kit for 24 Amp charging, and go with a 16 Amp setup instead. Thanks for the details on your 16 Amp kit. I already have the 5-20 UMC adapter. I will get the newly re-released 14-30 UMC adapter anyway, even if I don't make an extension cord for it.

    In case I do go ahead with a kit for 24 Amp charging, using L6-30 connectors and 10 gauge SOOW cable, is 50 feet the max length? What is the length of your "medium duty self-limiting charging kit #2?"

    One final question. :) By "self-limiting" are you referring to the UMC pilot signal that is triggered by the 5-20 and 14-30 UMC adapters, or something else?

    Thanks for your help,

    GSP
     
  6. linkster

    linkster Member

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    Kit #2 consists of (2) 25' L6-30 unmodified extensions along with (1) 15' L6-30 extension with a 10-30R.

    WRT to self-limiting, the car does not require the owner to manually reduce the amperage draw to a safe level.
     
  7. Rocky_H

    Rocky_H Member

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    By the way, here's a clarification on cable naming that I learned about from my electrician friend when I was getting my outlet installed. When they use that naming, like 10/3 or 6/3, that is telling how many of the thick wires are in it, but there is also an extra bare thin ground wire in the cable as well. So for a real 14-50 or 14-30 install, it needs Hot1, Hot2, Neutral, and Ground. That's three conductors plus ground, so you would use 10/3 or 6/3 or whatever.

    Sorry it seems like a long setup, but here's the point. If you are making an extension cable that just needs to carry 240V for Tesla charging, you only need 2 conductors plus ground, so you can use 10/2 cable for that. You just don't connect the Neutral. That saves weight and makes it more flexible. Obviously this is not "correct" for actual things that are supposed to have a neutral, like a real 14-30 outlet, but for Tesla charging, it works fine. Just label the cord that it's for Tesla charging only.
     
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