UMC charging at 120V with no ground. Would this work?

[F14Scott]

First, the backstory. Skip to the bottom for the actual question.

My AWD came with the 14-50, and I actually used it on my first road trip. We did an AirB&B over Memorial Day weekend, and I arrived there, after 15 minutes at the enroute Supercharger, at about 30% SOC, expecting to use the front door 120V outlet to trickle up for errands and the drive home.

But, the house was wired in the 1950s, and its 120V outlets were two wires only: hot and neutral but no ground. Without a ground on 120V, UMC no worky, I learned.

Fortunately, there was an RV campground about 200 yards down the road, so I gave the owner $10 to let me charge for a few hours on a 14-50. Worked perfectly: 32 amps and 30 MRPH.

The question:

If I bought a 3 prong adapter and then used a wire with two alligator clips to connect the tap on the adapter to something grounded (a metal pipe, the breaker box ground, etc.), would that work and be safe?

I'm pretty sure it would work, and my rationale is that if the ground failed or was faulted to a) the UMC would shut down the flow, and/or b) a breaker would trip. But, there are smarter electrical minds here than mine. What say you?

Pics:

 

[paulk]

It would work aside from the alligator clip thing. The little tab is supposed to have a screw going through it into it that is in the outlet box, which in old home is grounded via the armored wiring.

A ground wire can be a gauge lower than the supply wire, so at the smallest maybe 16 gauge solid copper. That reel looks like it’s stranded wire, which has higher resistance, and is likely thinner gauge. Also, clips aren’t reliable.

Of course, you want to know if it would work, even if it’s not a good idea. It might, and it probably wouldn’t be a fire hazard, but if you have no other choice I’d crank down the amps as low as possible to minimize risk.

 

[F14Scott]

Yeah, I tried the screw, but it didn't work, and, it not being my own house, I didn't want to mess with it.

I figured that, if the Tesla computer detected any ground, it would begin working. From what I understand, it doesn't use the ground, only detects that it is there. So, I thought, even if I had a tiny wire, it would enable the system, and if something went wrong and the whole load dumped to the tiny wire, the UMC would shut down. Come to think of it, I could include a fuse into my tiny ground wire for added safety.

 

[Lloyd]

If the wiring in the house is that old, I would not press it. You are likely to cause other problems.

 

[compu85]

Let's pull back a minute here....

First of all, don't put a fuse on the ground wire.

The ground is there so that if something on the AC side faults to the body it will trip the breaker, rather than zap the *sugar* out of you. Granted, the GFCI in the mobile connector should catch this, but why take the risk?

You want to install a proper ground. When an EVSE is connected to the car, the car body is connected to earth ground.

-J

 

[F14Scott]

Let's pull back a minute here....

First of all, don't put a fuse on the ground wire.

The ground is there so that if something on the AC side faults to the body it will trip the breaker, rather than zap the *sugar* out of you. Granted, the GFCI in the mobile connector should catch this, but why take the risk?

You want to install a proper ground. When an EVSE is connected to the car, the car body is connected to earth ground.

-J

Clearly, my designs to jury rig the system are not going well. I'll just stick to outlets that work. Glad I asked. Thanks, all.

 

[eprosenx]

First, the backstory. Skip to the bottom for the actual question.

My AWD came with the 14-50, and I actually used it on my first road trip. We did an AirB&B over Memorial Day weekend, and I arrived there, after 15 minutes at the enroute Supercharger, at about 30% SOC, expecting to use the front door 120V outlet to trickle up for errands and the drive home.

But, the house was wired in the 1950s, and its 120V outlets were two wires only: hot and neutral but no ground. Without a ground on 120V, UMC no worky, I learned.

Fortunately, there was an RV campground about 200 yards down the road, so I gave the owner $10 to let me charge for a few hours on a 14-50. Worked perfectly: 32 amps and 30 MRPH.

The question:

If I bought a 3 prong adapter and then used a wire with two alligator clips to connect the tap on the adapter to something grounded (a metal pipe, the breaker box ground, etc.), would that work and be safe?

I'm pretty sure it would work, and my rationale is that if the ground failed or was faulted to a) the UMC would shut down the flow, and/or b) a breaker would trip. But, there are smarter electrical minds here than mine. What say you?

Hrm, this is an interesting thought experiment. I will separate this into two parts:

1. How do you convince the Mobile Connector that the ground is valid?

The Mobile Connector is looking for voltage potential between one of the hot conductors (really in 120v, the only Hot conductor since the other is supposed to be neutral). I have read one thread where apparently Tesla support had explained how the Wall Connector injects DC into the ground or something in order to test to see if the voltage potential between the ground and the hot is "floating" or not. I am not sure how the Mobile Connector works exactly since it is different as it will accept both "two hots" type feeds, OR "one hot and one neutral".

2. How do you make this as safe as possible?

Man, I would not want to mess with wiring that old in general. Now, with that being said, one key would be to get a solid ground connection. Going just to a water pipe or an independent ground rod is a BAD idea. So the thing with the "ground" is that it provides (at least) a couple of functions. Yes, they do want it actually connected to earth ground, but perhaps the most important thing is that it is bonded to the neutral in a 120/240v split phase setup. This means that if a hot shorts to the ground it should flow enough current to instantly blow a breaker. If you have a poor ground (like a separate ground rod, etc...) the resistance may be too high to actually blow the breaker and open the circuit. Now maybe a poor ground would still be good enough for the GFCI in the UMC to trip (if the fault was downstream of the UMC), but if the fault was upstream of the UMC you don't get that GFCI protection.

I personally in this situation would be trying to identify the safest receptacle in the house to charge from. It is generally unlikely that NOTHING has been upgraded in the house since the days of two prong receptacles. Is there perhaps a modern receptacle in the kitchen on a 20a circuit with a ground? I would so use an extension cord (of appropriate gauge) over a two prong outlet jerry rigged together with a ground. ;-)

As always, post pictures of the panel! Maybe there is an easy solution... (120v receptacle right next to the main panel?)

 

[F14Scott]

Hrm, this is an interesting thought experiment. I will separate this into two parts:

1. How do you convince the Mobile Connector that the ground is valid?

The Mobile Connector is looking for voltage potential between one of the hot conductors (really in 120v, the only Hot conductor since the other is supposed to be neutral). I have read one thread where apparently Tesla support had explained how the Wall Connector injects DC into the ground or something in order to test to see if the voltage potential between the ground and the hot is "floating" or not. I am not sure how the Mobile Connector works exactly since it is different as it will accept both "two hots" type feeds, OR "one hot and one neutral".

2. How do you make this as safe as possible?

Man, I would not want to mess with wiring that old in general. Now, with that being said, one key would be to get a solid ground connection. Going just to a water pipe or an independent ground rod is a BAD idea. So the thing with the "ground" is that it provides (at least) a couple of functions. Yes, they do want it actually connected to earth ground, but perhaps the most important thing is that it is bonded to the neutral in a 120/240v split phase setup. This means that if a hot shorts to the ground it should flow enough current to instantly blow a breaker. If you have a poor ground (like a separate ground rod, etc...) the resistance may be too high to actually blow the breaker and open the circuit. Now maybe a poor ground would still be good enough for the GFCI in the UMC to trip (if the fault was downstream of the UMC), but if the fault was upstream of the UMC you don't get that GFCI protection.

I personally in this situation would be trying to identify the safest receptacle in the house to charge from. It is generally unlikely that NOTHING has been upgraded in the house since the days of two prong receptacles. Is there perhaps a modern receptacle in the kitchen on a 20a circuit with a ground? I would so use an extension cord (of appropriate gauge) over a two prong outlet jerry rigged together with a ground. ;-)

As always, post pictures of the panel! Maybe there is an easy solution... (120v receptacle right next to the main panel?)

There were, indeed, newer outlets inside the house that were grounded. It had had additions installed on both ends of the original house, both of which contained updated wiring. I even had a 12 gauge extension cord in my kit. But, I had no way of getting the cord outside without providing a mosquito path to inside, and I knew that, even though with 10 guests at the lake house all going in and out, any bite would be blamed on me and the towel-sealed cord through the window. No thank you...

Great info on the function of the ground. Thank you!

When my wife, who arrived a day before I did, couldn't get the car to charge, I threw this in my bag. It told me of the bad ground on all the outlets in the original house. When I related it to the owner, he explained the old wiring. Interestingly, the outlets were 3 prong (despite having no ground), so I'm guessing they had been installed more recently.

I put a bug in his ear to install a 14-50. I think it would be a great AirB&B feature.

 

[eprosenx]

There were, indeed, newer outlets inside the house that were grounded. It had had additions installed on both ends of the original house, both of which contained updated wiring. I even had a 12 gauge extension cord in my kit. But, I had no way of getting the cord outside without providing a mosquito path to inside, and I knew that, even though with 10 guests at the lake house all going in and out, any bite would be blamed on me and the towel-sealed cord through the window. No thank you...

Great info on the function of the ground. Thank you!

When my wife, who arrived a day before I did, couldn't get the car to charge, I threw this in my bag. It told me of the bad ground on all the outlets in the original house. When I related it to the owner, he explained the old wiring. Interestingly, the outlets were 3 prong (despite having no ground), so I'm guessing they had been installed more recently.

I put a bug in his ear to install a 14-50. I think it would be a great AirB&B feature.View attachment 420843

Hrm, yeah, so three prong outlets with the ground not connected to anything is not cool *unless* they are protected by a GFCI. I think I technically this can be allowed in certain circumstances and I think they must be labeled as such.

I thought your comments about the mosquitos being blamed on you were hilarious. I totally get it.

I would love to see a picture of the main breaker panel anyway. That is generally a really fast way to get a sense of how ancient a setup you are dealing with. But yeah, a 240v charging receptacle of any kind is a huge selling point for rentals. As an EV owner or makes a huge difference!

 

[Teskas]

Was in the same situation. This will work 100%. $1.50 adapter that you manually ground. I just stuck the end of the wire into my lawn.

 

[Frank99]

This will work 100%. ... I just stuck the end of the wire into my lawn.

It'll likely "work" in the sense that it'll convince the Mobile Connector that there's a valid ground and allow it to charge your car.
It'll likely not "work" in the sense that, should there be a fault that requires that ground to carry current to keep you (or one of your family) from smoking like an overcooked turkey, the resistance of your "ground" circuit will be too high to effectively save your heinie. I truly hope that situation doesn't occur.