Nema 6-20

[mknox]

also not to code but isn't ground effectively the same as neutral in this case? (e.g. connect the neutral pin to ground to satisfy the detection that might happen with a 14-50)

I would strongly advise against that. The ground conductor is usually bare and of a lesser gauge than the load-carrying conductors. While Neutral and Ground are bonded together in the service entrance panel, you could possibly end up with a unintended ground voltages at utilization points due to the natural resistance in the wire (if current ends up flowing back on the ground). We're already out on a limb with a 50 amp NEMA 6-50 on a 20 amp circuit.

 

[FlasherZ]

also not to code but isn't ground effectively the same as neutral in this case? (e.g. connect the neutral pin to ground to satisfy the detection that might happen with a 14-50)

It's a bad idea. The only place that ground == neutral is the bonding done in the service panel; everything else should be held separate, to keep ground conductors from becoming current-carrying conductors.

- - - Updated - - -

We're already out on a limb with a 50 amp NEMA 6-50 on a 20 amp circuit.

Oh, we're not out on a limb, we're jumping up and down on a 1" twig 50 feet from the ground.

While it may *seem* ok since the smaller wire is still protected by a smaller breaker, breaker failure is not unheard of (search for Federal-Pacific Panel Damage or Zinsco Panel Damage). Plugging another device into that socket -- or, let's say the Model S forgets the right charge level to use -- might cause a charge to either a) run for a short while, heating everything up before tripping the circuit breaker or b) draw the circuit's capacity without the 20% built-in safety level or c) worse. The NEMA 6-50 is really the only option you have short of re-engineering the circuit or adding something new, but it's still a really bad idea...

 

[cinergi]

Understood that that normally that's true. I was wondering whether, in this case, the ground would be at risk of carrying current if the car only connects to the hots (e.g. doesn't have a way to pull 120 from a 240).

 

[doug]

As far as I've heard it cares about all four wires.

You sure? The neutral on the Roadster UMC wasn't connected to anything.

 

[FlasherZ]

Understood that that normally that's true. I was wondering whether, in this case, the ground would be at risk of carrying current if the car only connects to the hots (e.g. doesn't have a way to pull 120 from a 240).

From what I understand, during normal cases the car only draws across the hot-hot of a 240V circuit and does not utilize the neutral (although may use voltage-sense circuitry to make sure wiring is correct), so yes - the only potential ground return is a failure. But the NEC assumes stupidity... So you have to guarantee that no other device -- potentially wanting to use that neutral pin -- would ever be plugged in there. That's a big risk, even if things are labeled - labels do fall off.

True story - as part of a partnership I once bought a property from the family of a man who had passed away. Apparently, the man had no NEMA 6 outlets and plugs around, so he wired a single NEMA 5-20 outlet with 240V and simply changed the plug on the appliance. Now, he obviously knew his secret and perhaps his family did... but imagine my surprise when, while cleaning things up, we plugged a shop-vac into that outlet. Result: 240 VAC 1, shop-vac 0. Now consider the confusion - most electronics nowadays can deal with 240VAC input, but imagine trying to troubleshoot (for a non-techie) when electronics work but motors and light bulbs all tend to explode.

The NEMA 6-50 outlet is a pretty bad hack and I can't recommend it, and anything else at this point IMHO should be considered life-threatening considering the size of circuits we're talking about.

 

[Cottonwood]

The NEMA 6-50 outlet is a pretty bad hack and I can't recommend it, and anything else at this point IMHO should be considered life-threatening considering the size of circuits we're talking about.

Take a look at what Tesla offers, Charging Adapters. The NEMA 10-30 is probably the best choice. Its not too far off on current (30 vs 20 Amps), uses the same 3 wires, and even if the breaker fails (pretty rare), you are only at 1.44x the rated power in the wire (24^2/20^2, what a 30 Amp device should draw vs the protected wire size).

BTW, older dryers that use the 10-30, assume that neutral=ground and power 120V lights, etc by taking one hot against ground. The modern neutral is connected to ground in one place practice is safe to the nth degree, but plenty of houses were wired with 10-30 for the dryer and 10-50 for the range, and nothing burnt down. I have charged my Roadster many times from 10-50 range outlets and 10-30 dryer outlers and been very happy...

 

[FlasherZ]

BTW, older dryers that use the 10-30, assume that neutral=ground and power 120V lights, etc by taking one hot against ground. The modern neutral is connected to ground in one place practice is safe to the nth degree, but plenty of houses were wired with 10-30 for the dryer and 10-50 for the range, and nothing burnt down.

True, the NEC revised to adopt single-ground to guard against double-failure and strange effects from potential differences between grounds in some cases. It was considered safe for many years, but is no longer. And FWIW, while many *didn't* burn down, there are some that created some really strange interactions and/or shocks. Do you want to risk it?

 

[strider]

Anyone know what the cost of the plug adapters for the UMC cost?

The Roadster ones are $100.

 

[Cottonwood]

True, the NEC revised to adopt single-ground to guard against double-failure and strange effects from potential differences between grounds in some cases. It was considered safe for many years, but is no longer. And FWIW, while many *didn't* burn down, there are some that created some really strange interactions and/or shocks. Do you want to risk it?

However, let's look at the risks. If you put a 10-30 on a wall in the garage, near one of the car bays and label it with current limits and a for car charging only label, its very safe for the Model S, it has such a strange plug on it that few people will even know what it is for, and even if they do wiggle a dryer into a strange corner of the garage, its no worse than a 90's electric dryer install.

I agree that Telsa should make a 6-20 adapter, but until they do, getting a 10-30 adapter, and using a 6-20 to 10-30 cheater cord or putting the 10-30 on the wall are pretty safe options. The cheater cord is closer to code (meets code for the permanent wall install) and the 10-30 on the wall is more convenient (no extra dangling cords; met code until 1996) and may let you charge at a higher current rating, depending on wire in the wall.

From NEMA connector - Wikipedia, the free encyclopedia:

As commonly used, 10–30 and 10–50 plugs have the frame of the appliance grounded through the neutral blade. This was a legal grounding method under the National Electrical Code for electric ranges and electric clothes dryers from the 1947 to the 1996 edition. Since North American dryers and ranges have certain parts (timers, lights, fans, etc.) that run on 120 V, this means that the wire used for grounding is also carrying current. Although this is contrary to modern grounding practice, such installations remain common in the United States and are relatively safe, because the larger conductors used are less likely to be broken than the smaller conductors used in ordinary appliance cords, and the current carried is small.​

 

[FlasherZ]

"Met code until 1996" I think is the key set of words. At one point, knob & tube wiring met code too... and there are plenty of homes still using it... but that doesn't mean it's still 100% safe, and it certainly doesn't mean you should install any new K&T wiring.

As I demonstrated with my 240VAC NEMA 5-15 example, above, it works as long as you're the one who deals with it. If you document it well, you reduce the risk but don't eliminate it, if someone else must deal with it. In some jurisdictions, just installing a new 10-30R or 10-50R is illegal, and you won't be able to sell your house until you remove it (as a non-permit, non-inspected install).

As for safety, at my great grandparents' house you learned pretty quickly not to touch the 1960's era (hot-hot-neutral) ungrounded oven and the stainless steel sink at the same time, since you'd get a "tickle" from it. I can tell you what I've learned over the years -- #1) people don't read labels, #2) electricity kills, and #3) just because it works doesn't mean it's safe.

Here's a final point to consider: if you live in an area where code is mandated / enforced, doing what you suggest may invalidate homeowner's insurance. If your home burns down, regardless of whether the hack caused it, the insurance company may be released from liability because you knowingly violated the currently-adopted version of the NEC in your jurisdiction and/or installed an improvement without permit and/or inspection. At a very minimum you might be forced to spend tens of thousands defending your position in court.

I can't stop anyone from doing it. I can even give my opinion on the best way to jerry-build something in a pinch. In this case, I'll just beg anyone reading this _not_ to engineer something this poorly when you're talking about these levels of current.

 

[dave]

Wow, thank you so much for the lively debate and solutions offered for my electrical issue! I am learning a ton just by reading your responses.

FYI, I'm going to pull off that receptacle to check the wiring here shortly to see if it's possible to bump it up to 30 Amps on the existing wire.

As far as the 10-30 to 6-20 adapter, let me recap to make sure I understand what you're saying. The old dryers that used 10-30 plugs would "create" 120V circuits by using ONE hot wire and the neutral. The danger here is that by using a "cheater" adapter, current would actually be put on the GROUND wire in such a scenario. Am I understanding that correctly? If that is the case, would it even be an issue plugging the Model S into it, since the car would only be using the full 240V on both hot wires, essentially leaving the Ground/Neutral unused? Are there any safety issues with not have a ground at all? I assume it can't be that dangerous, or Tesla wouldn't have made a 10-30 adapter which doesn't have a ground in it.

Thanks again for the education and suggestions!!

 

[doug]

I wouldn't bother with a 10-30. Where else are you going to use that? I'd figure out what current you can comfortably run and put in a NEMA 14-50 regardless. Just label it, be sure the car is dialed down, and don't use it for anything else.

 

[FlasherZ]

As far as the 10-30 to 6-20 adapter, let me recap to make sure I understand what you're saying. The old dryers that used 10-30 plugs would "create" 120V circuits by using ONE hot wire and the neutral. The danger here is that by using a "cheater" adapter, current would actually be put on the GROUND wire in such a scenario.

Not quite. Your first statement is true. A 10-30R or 10-50R is an UNGROUNDED service, meaning there is no separate safety grounding conductor. The neutral is used as that conductor in the case of a 10-30 or 10-50 connection, meaning the return path for 120V current is also shared with chassis ground. If you had a failure of the neutral conductor from the 10-30 or 10-50 back to the panel, it created a situation where the return current flow could return to ground through someone who touched the chassis and a ground at the same time (such as the oven-human-sink connection I spoke of earlier, or a barefoot human on concrete / in water).

If that is the case, would it even be an issue plugging the Model S into it, since the car would only be using the full 240V on both hot wires, essentially leaving the Ground/Neutral unused?

As to the best of my knowledge the car only uses 240V (hot to hot), this is correct, although you NEED some type of ground as a safety conductor. Otherwise, you can end up with a safety hazard. Imagine the case where a hot conductor on the charger gets frayed and comes in contact with the body of the car. You plug the charger in and the car is charging fine (because it only uses hot-to-hot). Then you touch the car with bare feet and end up as a path to ground for the potential voltage in the car's body. The grounding conductor is there to safely route electricity, and in this case trip the circuit breaker.

The car will also validate that there is not a ground fault - for safety reasons.

Are there any safety issues with not have a ground at all? I assume it can't be that dangerous, or Tesla wouldn't have made a 10-30 adapter which doesn't have a ground in it.

As mentioned above, yes! You must have some type of a safety ground. The 10-30 and 10-50 outlets gain access to ground reference through the neutral which is bonded at the transformer / service entrance to ground. So while there is safety built into it, it is also used as the return path in some cases.

 

[ElSupreme]

I wouldn't bother with a 10-30. Where else are you going to use that? I'd figure out what current you can comfortably run and put in a NEMA 14-50 regardless. Just label it, be sure the car is dialed down, and don't use it for anything else.

I would put whatever receptacle in the wall that will meet code. Then make up an 'adapter' cord that is about 6" long. The male end should fit your wall. The female end should fit whatever plug you choose for your Model S. You can even tie ground and neutral in a plug if you need/want to. This way your house wiring meets code. You can easily charge (and leave the adapter in place) whenever you want to.

McMaster-Carr

They are highish on price but have a really good website and inventory, and ship FAST!

 

[dave]

it works as long as you're the one who deals with it. If you document it well, you reduce the risk but don't eliminate it, if someone else must deal with it.

Thanks for the advice. I completely agree, and would not put an improper receptacle on the wall.

However, I am considering the adapter cable that would only be used by the Tesla. If I understand correctly, the only danger here is if the circuit-breaker fails and the car attempts to draw too much power due to not being dialed down correctly. Is that right? If I went with a 10-30 adapter, then even in the circuit-breaker failure scenario, the maximum current draw would only be moderately above spec, correct?

 

[mknox]

However, I am considering the adapter cable that would only be used by the Tesla. If I understand correctly, the only danger here is if the circuit-breaker fails and the car attempts to draw too much power due to not being dialed down correctly. Is that right? If I went with a 10-30 adapter, then even in the circuit-breaker failure scenario, the maximum current draw would only be moderately above spec, correct?

Your outlet is a 20 amp NEMA 6-20 which consists of two hot "legs" and a Ground (no Neutral). Tesla supports NEMA 6-50 which also only has two "legs" and Ground, although is rated for 50 amps. A "cheater cord" consisting of a NEMA 6-20 plug and a NEMA 6-50 socket would be a straightforward thing to wire. No utilizing a Ground for a Neutral. (The NEMA 10-30, while rated for lower amperage consists of two hot "legs" and Neutral (with no Ground) Not sure what the car would do with a neutral present, but if there were to be any current on the neutral, it would end up on the ground in your house wiring).

The caveat, and it's a big one, is that you have to dial down the charging rate on the car. In theory, your circuit breaker should trip on overcurrent, but as has been stated, circuit breakers can fail and if you overload that circuit, the wiring in your walls could start a fire.

You could wire 20 amp fuses into the cheater cord (using an approved enclosure) for added safety, but that cheater cord is going to look pretty weird.

 

[dave]

Update... the wiring is labeled AWG 10. I took the receptacle off the wall and there is another wire there that is not being used. (Neutral?)

Would this wiring be capable of any larger draws by replacing the receptacle and breaker?

 

[Lloyd]

You should be able to wire a 30 amp dryer receptacle and corresponding breaker to this. You might find that this is enough. I would charge at 25/24 amps with that setup.

 

[doug]

I would put whatever receptacle in the wall that will meet code. Then make up an 'adapter' cord that is about 6" long. The male end should fit your wall. The female end should fit whatever plug you choose for your Model S. You can even tie ground and neutral in a plug if you need/want to. This way your house wiring meets code. You can easily charge (and leave the adapter in place) whenever you want to.

McMaster-Carr

They are highish on price but have a really good website and inventory, and ship FAST!

This is good advise.

 

[FlasherZ]

Yes, the white is reserved for neutral. That's good news...

If you want to use the existing wiring, your best bet would be to replace that outlet with a NEMA L14-30 (twistlock), the kind that generators usually have on them. Then the only thing you have to do is replace the breaker with a 2-pole 30A breaker and make sure the neutral wire is hooked up in the panel to the neutral bus. You may have clearance problems in that box because a L14-30 receptacle is pretty big, but you can find some single-gang receptacles out there.

Then, you can either use the L14-30 adapter for the UMC (if you want the correct solution), or you could buy an RV conversion cord and use the NEMA 14-50 plug that comes with the UMC:
Camco 55422 Power Grip 12 50 Amp Female to L14-30 Male RV Generator Adapter : Amazon.com : Automotive

This would let you charge at 24A within spec... out-of-spec you could probably push up a bit.