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n2mb_racing

Active Member
Jun 14, 2014
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durham, NC
I thought I would make a new post with pictures I took while building my NEMA 6-20P to NEMA 5-20R Adapter. This adapter allows you to charge at 12A or 16A at 240V from a NEMA 6-20 receptacle. The NEMA 6-20 receptacle is easy to install if you have an existing 120V outlet on its own dedicated circuit, with 12 gauge, 3 conductor wire. You just change the breaker in your box to a 240V breaker, move the neutral to the second hot and then swap out the 120V receptacle for a 240V, NEMA 6-20 receptacle. If that is confusing, ask your electrician for help.

The benefit is you go from charging at 3-4 MPH to charging at 8 MPH @ 12A or 11 MPH @ 16A. If you are fine charging at 8 MPH, stop here and go buy the Tesla NEMA 6-15 adapter (Tesla — NEMA 6-15) and you can avoid building this. If you want 16A charging, you'll need the Tesla NEMA 5-20 adapter (Tesla — NEMA 5-20) as well.

The upside is you can almost always charge the car overnight (depending on your usage), and you get 90+% efficient charging from 240V, vs ~70% efficient charging from 120V.

Parts:
NEMA 6-20P 1 foot cable for $15:
Amazon.com: NEMA 6-20P to C19 Power Cord - 1 Foot, 20A/250V, 12/3 SJT - Iron Box # IBX-4937-01M: Home Audio & Theater

But, given the trouble I had assembling this, I would recommend getting a slightly longer (3ft) cable instead for a few dollars more:
Amazon.com: NEMA 6-20P to C19 Power Cord - 3 Foot, 20A/250V, 12/3 AWG - Iron Box # IBX-4937-03: Home Audio & Theater

NEMA 5-20R socket for $11
Leviton 5369-C 20 Amp, 125 Volt, Connector, Industrial Grade, Straight Blade, Grounding, Black-White - Electric Plugs - Amazon.com

Steps:
  1. Lay out all the tools you need. I would recommend a different wire stripper. My automatic wire stripper did not work so well for this. View media item 116576
  2. Cut off the C19 end of the cable. It is not needed. View media item 116577
  3. Follow the instructions provided to attach the NEMA 5-20 receptacle to the wire. I found that I needed to remove the extra insert in the cable clamp, since the cable was larger than the guide size. View media item 116578
  4. Carefully strip off the outer insulation using a razor or another tool. Be careful not to damage or knick the insulation of the wires within. This was the hard part. I messed this up several times and had to strip farther and farther back, which made my adapter shorter than I originally planned for in the end. In retrospect, I'd recommend starting with the 3 ft or longer cable so that you have more core to work with when you invariably mess up. View media item 116579
  5. Strip the inner conductors as shown in the receptacle instructions. If you mess up here, just start over at step 4 and strip back more of the outer jacket... If I did it over again, I would recommend leaving about 3/16" more of the insulated wires exposed than the instructions recommended. The bare copper length was good. It was very difficult to get the wires into their respective sockets with the wires stripped as recommended. A bit more length of the insulated portion of the wire would make it easier. Just make sure to not expose too much. The cable clamp needs to clamp down on the outer jacket, not the inner wires. View media item 116580
  6. Assemble the plug. The only important connection is GREEN to the ground terminal (GREEN). Both the white and black wires will be hot, so they are interchangeable. Be sure to slip the cover over the wire before starting the assembly. View media item 116581View media item 116582
  7. Check to make sure all the wires are inside the screw terminals and there are no flyaways (bare strands) protruding out of the wire guides. View media item 116583
  8. Screw on the cover and tighten the cable clamp down on the wire jacket. View media item 116584View media item 116585
  9. Be sure to label your adapter: "Warning 240V: TESLA Charging ONLY!". Plugging a normal device into this adapter might cause damage, so it is good to warn people.
 
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BerTX

Active Member
Supporting Member
May 2, 2014
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Texas/Washington
Nice! There have been several people wanting to do this lately, so this will help a lot.

One thing I noticed was missing is that the 120v white neutral wire should be wrapped with black tape both in the box and at the outlet to indicate its use as a hot wire on the new 240v circuit.
 

n2mb_racing

Active Member
Jun 14, 2014
1,328
1,170
durham, NC
Nice! There have been several people wanting to do this lately, so this will help a lot.

One thing I noticed was missing is that the 120v white neutral wire should be wrapped with black tape both in the box and at the outlet to indicate its use as a hot wire on the new 240v circuit.

Good point. I can't edit the original post, but yes, everyone should do that in the outlet box and in the circuit breaker.
 

BerTX

Active Member
Supporting Member
May 2, 2014
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While I am sure you are quite right, I think that detail is inconsequential compared to the whole project of building this being one big fat code violation. ;)

It is several code violations -- which is bothering you? If I were doing it, I'd build a 6-20 to 14-50 adapter and cut back on the charge amps on the car. Chances are you'd only use it at home, so the car would remember the charge rate, although I've heard people say the car forgets sometimes on firmware updates.

Would that be less irksome?
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,093
8,718
Boise, ID
It is several code violations -- which is bothering you? If I were doing it, I'd build a 6-20 to 14-50 adapter and cut back on the charge amps on the car. Chances are you'd only use it at home, so the car would remember the charge rate, although I've heard people say the car forgets sometimes on firmware updates.

Would that be less irksome?
You have this totally backward. I am the one who is not bothered at all. Perhaps that wasn't clear, or my humor was too subtle. I was pointing out that since this entire enterprise of building adapter pigtails from one outlet type to another and one voltage level to another is just something we have to do, but is way outside of code compliance, it seemed pretty nitpicky and silly for someone to bring up whether the cord was indoor or outdoor rated. I actually did put the winky face there at the end to explicitly show the humor.
 

miimura

Well-Known Member
Aug 21, 2013
6,701
6,547
Los Altos, CA
It is several code violations -- which is bothering you? If I were doing it, I'd build a 6-20 to 14-50 adapter and cut back on the charge amps on the car. Chances are you'd only use it at home, so the car would remember the charge rate, although I've heard people say the car forgets sometimes on firmware updates.

Would that be less irksome?
As long as you keep this pigtail in your car and don't let other people plug anything else into it, it's much safer than what you propose - removing the EVSE's ability to properly set the pilot signal. If you make or use a 6-20 to 14-50 adapter pigtail, you must religiously check the current setting in the car EVERY SINGLE TIME to make sure it will not draw more current than the circuit can support.
 

BerTX

Active Member
Supporting Member
May 2, 2014
3,505
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Texas/Washington
You have this totally backward. I am the one who is not bothered at all. Perhaps that wasn't clear, or my humor was too subtle. I was pointing out that since this entire enterprise of building adapter pigtails from one outlet type to another and one voltage level to another is just something we have to do, but is way outside of code compliance, it seemed pretty nitpicky and silly for someone to bring up whether the cord was indoor or outdoor rated. I actually did put the winky face there at the end to explicitly show the humor.

I got that you were amused, I guess I somehow thought you were amused and upset. Oh well, apologies.
 

BerTX

Active Member
Supporting Member
May 2, 2014
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Texas/Washington
As long as you keep this pigtail in your car and don't let other people plug anything else into it, it's much safer than what you propose - removing the EVSE's ability to properly set the pilot signal. If you make or use a 6-20 to 14-50 adapter pigtail, you must religiously check the current setting in the car EVERY SINGLE TIME to make sure it will not draw more current than the circuit can support.

So wiring a 240v plug to carry 240 volts and setting the amperage draw is worse than using a 125v rated plug for 240v, against manufacturer's directions for a purpose it was not intended?

And I explained that the car remembers the amperage setting, unless it doesn't. You wouldn't have to religiously check it. If the amperage setting reverts to 40A, the sky will not fall.

I don't think there is likely to be a problem with either, but I don't think one is safer than the other. But I'm not an electrician nor an EE nor any type of expert, so I can be convinced.
 

miimura

Well-Known Member
Aug 21, 2013
6,701
6,547
Los Altos, CA
So wiring a 240v plug to carry 240 volts and setting the amperage draw is worse than using a 125v rated plug for 240v, against manufacturer's directions for a purpose it was not intended?

And I explained that the car remembers the amperage setting, unless it doesn't. You wouldn't have to religiously check it. If the amperage setting reverts to 40A, the sky will not fall.

I don't think there is likely to be a problem with either, but I don't think one is safer than the other. But I'm not an electrician nor an EE nor any type of expert, so I can be convinced.
If you look at the Leviton or Hubbell screw-together 5-20R and 6-20R cord sockets, I doubt you'll see any design difference in order to support 250VAC vs. 125VAC. The only difference is the blade orientations, not the actual insulation ratings or design. So, to me the issue of safely operating a 5-20R at 240VAC with the UMC is a non-issue. As I said above, the danger is to equipment that could be plugged into this pigtail that would be damaged by the 240VAC supply.

On the other hand, you claim that "the sky will not fall" if the car reverts to 40 amps and you don't notice. There actually is a real chance of danger in this case. Circuit breakers are not perfect. Sure, a 20 amp breaker should trip very quickly when passing 40 amps, but if it doesn't, things will melt and potentially catch fire.

On balance, I would say that using the 6-20P to 5-20R pigtail and having the UMC systematically signal 16 amps to the car is safer than using a 6-20P to 14-50R pigtail. Obviously, the best solution would be for Tesla to make and sell a 6-20 UMC adapter.
 

BerTX

Active Member
Supporting Member
May 2, 2014
3,505
3,647
Texas/Washington
If you look at the Leviton or Hubbell screw-together 5-20R and 6-20R cord sockets, I doubt you'll see any design difference in order to support 250VAC vs. 125VAC. The only difference is the blade orientations, not the actual insulation ratings or design. So, to me the issue of safely operating a 5-20R at 240VAC with the UMC is a non-issue. As I said above, the danger is to equipment that could be plugged into this pigtail that would be damaged by the 240VAC supply.

On the other hand, you claim that "the sky will not fall" if the car reverts to 40 amps and you don't notice. There actually is a real chance of danger in this case. Circuit breakers are not perfect. Sure, a 20 amp breaker should trip very quickly when passing 40 amps, but if it doesn't, things will melt and potentially catch fire.

On balance, I would say that using the 6-20P to 5-20R pigtail and having the UMC systematically signal 16 amps to the car is safer than using a 6-20P to 14-50R pigtail. Obviously, the best solution would be for Tesla to make and sell a 6-20 UMC adapter.

As I said, I don't think either is a problem.

If you have to fall back on the possibility of defective wiring or overload protection as a reason -- well that is no more likely on one circuit than another.

And the plugs look the same -- except for the voltage rating stamped on it.

I don't really care. If you think one method is better than another, I'm fine with going along with that.
 

n2mb_racing

Active Member
Jun 14, 2014
1,328
1,170
durham, NC
It is several code violations -- which is bothering you? If I were doing it, I'd build a 6-20 to 14-50 adapter and cut back on the charge amps on the car. Chances are you'd only use it at home, so the car would remember the charge rate, although I've heard people say the car forgets sometimes on firmware updates.

Would that be less irksome?

I've built the 6-20 to 14-50 adapter as well. The 14-50 socket is a bit large and unwieldy. Also, it isn't really designed to accept 12 gauge wire, so I'm not super confident in it. The NEMA 5-20R is designed to work well with 12 gauge wire.

I also tested what happens with the 6-20 to 14-50 adapter if the charge current exceeds the limit. It seems like my breaker was not going to trip at 30 amps. It only tripped when I went to 40 amps, and it took some time to do it.
 
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