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Extension cords: NEMA 14-30, 10-30, 6-50, or 6-20...

n2mb_racing

Active Member
Jun 14, 2014
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2,126
durham, NC
I'd like to retire my NEMA 14-50 extension cable. It's too short (15 ft) and too heavy, since it has four 6 gauge wires. It's overkill for charging at dryer outlets at 16A to 24A. So, I'm weighing what to get next. My primary use will be at a NEMA 10-30 dryer outlet, with some occasional NEMA 14-30 dryer outlets. I need just over 25 ft. I usually have a full weekend to charge, so I'd likely do 16A charging regardless of the cable type to be conservative.

Options:
1. NEMA 10-30 50ft extension. $112 Amazon.com
Upside: Cheap, 10 gauge wires, only three conductors, so no wasted weight for a neutral that I'll never use.
Downside: needs an adapter to plug into most common NEMA 14-30 dryer outlets, and likely would send neutral to the NEMA 10-30R, rather than ground. However, on a dedicated 240V circuit that doesn't use 120V ever, is there really a difference between ground and neutral? I can't see one.

2. NEMA 6-20, 50 ft extension. $90 https://www.amazon.com/Parkworld-Extension-6-20P-Female-Adapter/dp/B089QGB674
Upside: Cheaper, I already own the NEMA 6-20 UMC plug. Lightweight. Fast enough charging to get a full charge in 24 hours.
Downside: 12 gauge wires, so have to limit charging to 16A. Not up to code, since 12 gauge is too small for 30A, though the UMC will only pull 16A with the 6-20 plug. However, there are adapters that include 20A breakers, so that should improve the safety of the setup. Amazon.com

3. NEMA 14-30 extension. two 25 ft cables, $70 each,
Upside: direct connection to modern dryers. 10 gauge wires.
Downside: useless neutral wire, more expensive. Hard to find a cable longer than 25 ft.

4. NEMA 6-50 extension. 50 ft $75 Amazon.com
Upside: Cheap because used for welders. Many options available.
Downside: Needs an adapter from both 10-30 and 14-30 to 6-50. Also need to manually dial down the UMC current to 24A, when using the 6-50 UMC plug.
 
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GSP

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Supporting Member
Dec 28, 2007
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I like option 1 the best, since you can charge at up to 24 Amps if needed.

Several years ago I spent some time thinking about ”extension cord“ options, and discussing with TMC members. I wanted a solution that was lightweight, 70’ to 100’ long, useable with any 120 or 240 V outlet, and did not require manually setting the current on the touch screen [in case I ever forgot to do so]. I ended up with a “J1772” extension from Quick Charge Power. It has a Tesla inlet on one end, and a J1772 plug on the other. QCP made a special 60’ long version at my request [+ 25’ UMC = 85’ total]. It is an expensive solution, but it is both lightweight and capabable of up to 40 Amp charging. It also allows me to use all the Tesla UMC adapters, so no need to select Amps on the touch screen. Another advantage is the entire extension is protected by the UMC ground fault detection, which is not the case with upstream extension cords. The light weight 40 Amp capability is achieved using the same special cable that Tesla used for their Gen1 40 Amp UMC, which has two conductors for each of the hot connections. Two smaller wires are lighter weight and more flexible than one large wire of the same ampacity.

I have only used it a few times, but it is nice to have the “ultimate solution” when needed.

GSP
 
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n2mb_racing

Active Member
Jun 14, 2014
2,281
2,126
durham, NC
I like option 1 the best, since you can charge at up to 24 Amps if needed.

Several years ago I spent some time thinking about ”extension cord“ options, and discussing with TMC members. I wanted a solution that was lightweight, 70’ to 100’ long, useable with any 120 or 240 V outlet, and did not require manually setting the current on the touch screen [in case I ever forgot to do so]. I ended up with a “J1772” extension from Quick Charge Power. It has a Tesla inlet on one end, and a J1772 plug on the other. QCP made a special 60’ long version at my request [+ 25’ UMC = 85’ total]. It is an expensive solution, but it is both lightweight and capabable of up to 40 Amp charging. It also allows me to use all the Tesla UMC adapters, so no need to select Amps on the touch screen. Another advantage is the entire extension is protected by the UMC ground fault detection, which is not the case with upstream extension cords. The light weight 40 Amp capability is achieved using the same special cable that Tesla used for their Gen1 40 Amp UMC, which has two conductors for each of the hot connections. Two smaller wires are lighter weight and more flexible than one large wire of the same ampacity.

I have only used it a few times, but it is nice to have the “ultimate solution” when needed.

GSP
That's quite nice!
 
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Rocky_H

Well-Known Member
Feb 19, 2015
8,620
11,203
Boise, ID
I do have a 30 foot full 14-50 cable, and it is ridiculously heavy and cumbersome because of the extra full sized wire for neutral, which isn't needed.

I think the important priorities for using it a lot would be decent wire gauge, and only having the two full sized conductors for voltage so it doesn't have that extra weight and bulkiness. But that will mean that you would need to get a little pigtail to adapt it to 10-30 on one end or the other, since that does a little hand waving of Neutral remapped to ground.

So I think the best thing for this is a custom EV charging extension cord, which a few places make. I Googled and found one that is basically what I would get in this situation:


It uses 8 gauge wire, so is a little more margin for 30A circuits than using just 10 gauge. It only has the two wires plus ground. The plug on the end is a 14-XX universal that doesn't have a neutral pin, so it can plug directly into either 14-50 or 14-30.

And I personally have cut the L shaped Neutral pin off of my Tesla 14-30 adapter, so I could use it with this cord, which would still enforce the 24A limit.
 
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n2mb_racing

Active Member
Jun 14, 2014
2,281
2,126
durham, NC
Or I could do the sketchiest option, this adapter: https://www.amazon.com/gp/product/B078PHY3ZJ/
and a 120V extension cable and NEMA 5-15 or 5-20 UMC plug.

Totally sketchy, but really no different than a 6-20 extension cable. The UMC doesn't care about the voltage. The plugs only set the current.

Other than the potential for someone else to use the outlet and blow something up that is expecting 120V and gets 240V. 😅
 
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n2mb_racing

Active Member
Jun 14, 2014
2,281
2,126
durham, NC
Yes, true. I did get a 10 gauge 5-20 extension from Amazon called the "Yellow Jacket". That should be able to support 24A, but I would likely turn it down a little anyway because of the extra plug connections.
Even with 10ga, the plugs are only rated for 16A continuous, so I wouldn't exceed that. I've thought about using a cable like that, since I already have one. But, I don't know if the built-in neon light is going to handle 240V when it is designed for 120V. IT might burn out.
 
Oh, heh. That is an interesting point. I haven't tried to use 240V on it yet and hadn't been planning to.
Some quick googling suggests that using a neon lamp with resistor sized for 120V on 240V will just make the neon light much brighter and it will burn out sooner, but other than that, probably not much difference. As long as the resistor is large enough to handle a bit of extra heat, it should be ok. If it is on 24/7, the light may burn out sooner than decades, but I'm not sure if I care. Still probably not a great option, but an interesting one.
 
Update: I bought the 50ft NEMA 10-30 extension. It was $108 before tax. It's actually far cheaper than buying 50ft of 10/3 wire at the hardware store. I'm using it now. It seems to be high quality, no complaints on the cord. It's still quite thick and heavy. It's a bigger jump up from 12/3 than I was expecting.

However, it turned out the outlet was never hooked up! So, I had to finish running the wires into the breaker box. Oddly, they ran 10/4, but installed a new NEMA 10-30 outlet. There may have been an old NEMA 10-30 outlet in that location, but possibly not. Also strange they installed a 20A breaker. No big deal, I'm charging at 16A. I hooked up the ground wire in the panel. If we do end up getting a dryer, I'll swap it for a NEMA 14-30 for safety and swap to a 30A breaker.
 
Also bought this adapter for $13.99 to plug my 10-30 extension into 14-30 outlets. It seems very well made. I can't believe it is this inexpensive.

Disclaimer: this is totally an unsafe cord for use with dryers and shouldn't be used for dryers. If you have a 10-30 dryer and a 14-30 outlet, just take the extra 20 minutes and install a new 14-30 cord on the old dryer to make it safe.

However, it should be safe for 240V only devices, like EV charging. Not really up to code, since you will be using the neutral as ground, but I can't see the difference between the two on a dedicated circuit, other than convention.
 
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Also bought this adapter for $13.99 to plug my 10-30 extension into 14-30 outlets. It seems very well made. I can't believe it is this inexpensive.

Disclaimer: this is totally an unsafe cord for use with dryers and shouldn't be used for dryers. If you have a 10-30 dryer and a 14-30 outlet, just take the extra 20 minutes and install a new 14-30 cord on the old dryer to make it safe.

However, it should be safe for 240V only devices, like EV charging. Not really up to code, since you will be using the neutral as ground, but I can't see the difference between the two on a dedicated circuit, other than convention.
A dryer with a 10-30 plug would not be any less safe plugged into this adapter vs. plugged into a "real" 10-30 socket, but rewiring the dryer with a proper 14-30 cord would be the much better choice.

There's really no difference between using this adapter for a dryer vs an EVSE—both are potentially unsafe. Not having a proper ground anywhere you've got 240V is just a bad idea, especially when there might be water around. To wit: Does ClipperCreek Have an EVSE that Plugs into a NEMA 10-30 Outlet?

While the neutral and ground in a modern house are electrically connected (bonded) at the main panel, they should never be connected anywhere else and it is possible for the neutral to become energized if some piece of equipment connected to the neutral malfunctions. That's one reason why 10-30 is no longer allowed for new work.

It would be safest to just go ahead and replace that outlet with a 14-30 since the wires are all there. Of course, that won't help you with your extension cord. Personally, I would be reluctant to use such an extension cord anywhere where water ingress might be possible, especially outside. That would include anywhere where the car itself could potentially get wet or be parked on wet ground.
 
A dryer with a 10-30 plug would not be any less safe plugged into this adapter vs. plugged into a "real" 10-30 socket, but rewiring the dryer with a proper 14-30 cord would be the much better choice.

There's really no difference between using this adapter for a dryer vs an EVSE—both are potentially unsafe. Not having a proper ground anywhere you've got 240V is just a bad idea, especially when there might be water around. To wit: Does ClipperCreek Have an EVSE that Plugs into a NEMA 10-30 Outlet?

While the neutral and ground in a modern house are electrically connected (bonded) at the main panel, they should never be connected anywhere else and it is possible for the neutral to become energized if some piece of equipment connected to the neutral malfunctions. That's one reason why 10-30 is no longer allowed for new work.

It would be safest to just go ahead and replace that outlet with a 14-30 since the wires are all there. Of course, that won't help you with your extension cord. Personally, I would be reluctant to use such an extension cord anywhere where water ingress might be possible, especially outside. That would include anywhere where the car itself could potentially get wet or be parked on wet ground.

It's unsafe with a dryer because dryers have 120V motors and 240V heating elements. So, they intentionally pass current through the neutral. Thus, if the neutral breaks, you get 240V on the body of the dryer and you die.

EV charging never passes current through the neutral or ground. It tests if there is a connection to ground by passing a tiny current to make sure the ground wire is present. And they use the ground wire to keep the car body at ground.

I agree, you should never bond neutral and ground. The adapter doesn't do that. It connects neutral to the 10-30 "third wire", which the Tesla UMC uses as ground. So, technically, I could fix the NEMA 14-30 to 10-30 adapter by connecting the ground wire at the 14-30 to the third pin of the 10-30, and leaving the neutral from the 14-30 disconnected.

But, I still fail to see the house wiring difference between the two. Both wires at a NEMA 14-30 receptacle will be dedicated 10 awg or heavier wires that run back to the main panel, then get bonded together. There's nothing else on the circuit.

Either way, though, you still have a "ground" at the UMC.
 
But, I still fail to see the house wiring difference between the two. Both wires at a NEMA 14-30 receptacle will be dedicated 10 awg or heavier wires that run back to the main panel, then get bonded together. There's nothing else on the circuit.

Either way, though, you still have a "ground" at the UMC.
There is a case where it can make a difference. If the 10-30 is fed from a subpanel, then the neutral can have return voltages on it from the other circuits in the subpanel. I had that case at a previous house and believe it may be why an EVSE (for my LEAF) I plugged into that 10-30 to test blew internal components. After getting it repaired, I never tried it again.

The only way to use that sort of a circuit is to either run a separate ground wire and change to a 14-30, or move the neutral wire to the ground bar in the subpanel, and change to a 6-30 (in which case it can't be used for a dryer). Someone doing the second option should mark both ends of the neutral wire with green tape to identify it as a ground.
 
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There is a case where it can make a difference. If the 10-30 is fed from a subpanel, then the neutral can have return voltages on it from the other circuits in the subpanel. I had that case at a previous house and believe it may be why an EVSE (for my LEAF) I plugged into that 10-30 to test blew internal components. After getting it repaired, I never tried it again.

The only way to use that sort of a circuit is to either run a separate ground wire and change to a 14-30, or move the neutral wire to the ground bar in the subpanel, and change to a 6-30 (in which case it can't be used for a dryer). Someone doing the second option should mark both ends of the neutral wire with green tape to identify it as a ground.

Ahh good point! That is one situation I hadn't thought about.

In that case, the adapter from NEMA 14-30P to 10-30R could be fixed to run hot hot and ground to the UMC (omitting the neutral), and it would be fine. Not good for a dryer, but fine for the UMC, since it never uses the neutral anyway.
 
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