Insufficient grounding with metal conduit

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Has anyone seen insufficient grounding error message with charging at 120v? I live in an older house and my garage/house is grounded through metal conduit

 

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Strange part is that sometimes it will charge and other times it wont

 

[Originalando]

I am working through some issues with charging via 120v at my apartment as well. Originally I would get occasional grounding errors when the temp outside dropped below 50°F. Now I get additional "unable to charge" errors every time. I know its not my UMC as it works fine at other locations.

Recently I decided to check the outlet terminals and found out there is some serious underlying issues. My hot to neutral show the expected 120v, but my neutral to ground shows 30v and ground to hot shows 90v. After multiple attempts to get my complex to understand there's an issue (more than what the maintenance guy should be dealing with) they finally have an electrician coming out this week.

EDIT: Also, I see you too are in the Chicago area. Metal conduit is code out here, every house/building I have lived in out here uses it as the ground circuit since its cheaper than running the additional ground wire.

 

[Olle]

Yes, the car doesn't like when you have too much resistance between ground and neutral. IEEE recommends <5 Ohms. Here is a good article about this.

The reason is obviously that sitting on isolating rubber tires and without a low resistance ground connection, even a minute leakage current from the charge voltage can make the car dangerous to touch, so you are lucky that the car gives you a warning.

To be safe you should measure your local ground connection. To make the car happy, all you need to do is tighten down your neutral and grounding conductors/conduits from the outlet all the way up to where they bond in the service panel, until you have 0 ohm between them. Theoretically you could still get shocked but the car will charge since it can't know what "real" ground is. I don't condone that as a sole measure though.

Side note: It's pretty common with bad /no ground. Our house had a modern looking electrical system with new panels, outlets and switches throughout. I assumed everything was fine until I discovered we had no ground in places. Turned out the installer had just thrown the grounding conductor of a major sub panel into the service panel without connecting it to anything. Same with our salt water pool pump installers, they left all grounding and bonding conductors hanging inside the boxes, which I discovered after a year. Nobody got electrocuted in the meantime. Phew.
Heard same story from others.
The paradigm among some installers seem to be "ground doesn't do anything so why bother, I get paid the same no matter".

 

[Regaj]

Yes, the car doesn't like when you have too much resistance between ground and neutral. IEEE recommends <5 Ohms. Here is a good article about this.

The reason is obviously that sitting on isolating rubber tires and without a low resistance ground connection, even a minute leakage current from the charge voltage can make the car dangerous to touch, so you are lucky that the car gives you a warning.

To be safe you should measure your local ground connection. To make the car happy, all you need to do is tighten down your neutral and grounding conductors/conduits from the outlet all the way up to where they bond in the service panel, until you have 0 ohm between them. Theoretically you could still get shocked but the car will charge since it can't know what "real" ground is. I don't condone that as a sole measure though.

Unfortunately, establishing a good ground is a bit more complicated than tightening down all connections. And creating a ground system at a residence that is anywhere close to 5 Ohms isn't practical. That spec for <5 Ohms is for things like communications sites, like cell towers, and typically costs thousands of dollars to achieve.

The NEC, the source for the electric code in most of the United States, requires 25 Ohms for grounding systems at residences. Alas, most electricians have neither the equipment nor the experience to perform the Fall of Potential test to determine the resistance of that grounding system they just installed. More importantly - and more worryingly - in very, very few cases will that ground system installation come anywhere near 25 Ohms. Soil resistivity, temperature, moisture and a few other factors all come into play for that.

For context, I sank an eight-foot ground rod at my house last summer which measured 135 Ohms. And Mike Holt, the well-known educator in the electrical industry space, did a test where he sank an eight-foot ground rod to a distance of ten feet... which then measured 265 Ohms. You can reduce your resistance and improve your ground system by installing your ground rod deeper, or by having multiple rods, bonded together. The NEC tacitly acknowledges this reality... the second part of their residential spec is to simply install two ground rods and call it good. No measurement needed.

And sorry, no, measuring for zero Ohms isn't going to be helpful. All circuits have resistance. You can do things to lower it (like sinking that second ground rod), but you can never get it to zero.

Loose connections and incorrect connections are certainly a thing, and should be the first thing that a homeowner looks for when they have a grounding problem, like the OP in this thread. Having a good electrician inspect what you have is certainly recommended, for the vast majority of people, whenever there's any question.

Poor grounding can be much more serious than a car that won't charge.

 

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I used one of those plugs to check if grounding/hot/neutral are correct.

Interesting that I’m finding that when I open/close the garage door the light for ground goes from bright to dim. I was seeing lower voltage warnings at 12 amps when opening the garage but lowered amps and have not seen problems since.

With the Tesla plugged in I am often seen the ground light completely go off and on but it’s random. Sometimes flashes, sometimes always on, sometimes always off. At one point I did see the ground/neutral switched light come on but that was just for a short period.

I got shocked from the light switch out there in the summer. I had an electrician come out and look at it and all he did was changing the light switch. He said it was old and close to the conduit but that he didn’t sound like it was 100% what caused it.

I can have the electrician out again at some point but trying to save some $ after my Tesla purchase. My biggest concern is safety. It’s seems like the Tesla is smart enough to stop charging if there is an issue. That doesn’t bother me. I just want to make sure it’s safe.

I work from home so mainly drive it on the weekend. It’s just sitting in the garage at about 70-80% charge. I’m happy to just leave it there until the weekend but I know people recommend keeping it plugged in when not used, especially since the weather is getting cold in Chicago.

 

[davewill]

I used one of those plugs to check if grounding/hot/neutral are correct.

Interesting that I’m finding that when I open/close the garage door the light for ground goes from bright to dim. I was seeing lower voltage warnings at 12 amps when opening the garage but lowered amps and have not seen problems since.

With the Tesla plugged in I am often seen the ground light completely go off and on but it’s random. Sometimes flashes, sometimes always on, sometimes always off. At one point I did see the ground/neutral switched light come on but that was just for a short period.

I got shocked from the light switch out there in the summer. I had an electrician come out and look at it and all he did was changing the light switch. He said it was old and close to the conduit but that he didn’t sound like it was 100% what caused it.

I can have the electrician out again at some point but trying to save some $ after my Tesla purchase. My biggest concern is safety. It’s seems like the Tesla is smart enough to stop charging if there is an issue. That doesn’t bother me. I just want to make sure it’s safe.

I work from home so mainly drive it on the weekend. It’s just sitting in the garage at about 70-80% charge. I’m happy to just leave it there until the weekend but I know people recommend keeping it plugged in when not used, especially since the weather is getting cold in Chicago.

Are those garage plugs on a subpanel? Your description makes me think perhaps neutral and ground have been bonded together somewhere they shouldn't be, like in the subpanel. I suppose it could be in one of the electical boxes as well. Ground and neutral should only be connected together at the main service panel. If it's done anywhere else, it can cause the ground to have return voltages on it. Another way this can happen is inside an appliance either because of a broken/worn wire, or because someone tried to repair or replace a power cord and wired it wrong. It also happens if a homeowner installs a light fixture incorrectly.

 

[Olle]

I think we are saying the same thing even though you wrote "unfortunately" "sorry" "no" as response to my post.

Unfortunately, establishing a good ground is a bit more complicated than tightening down all connections.

I don't think you read this part:

Theoretically you could still get shocked but the car will charge since it can't know what "real" ground is. I don't condone that as a sole measure

And sorry, no, measuring for zero Ohms isn't going to be helpful. All circuits have resistance. You can do things to lower it (like sinking that second ground rod), but you can never get it to zero.

Correct, you can't get absolute zero. You should get 0 but probably not 0.1 if we are thinking in significant digits, where 0 means <.5 and 0.1 means <.05 and so on.

for OPs outlet, say 12AWG and 200 Ft roundtrip that would give 200/1000*1.588=0.32 Ohms.

My house btw after reconnection of sub panel ground in service panel.

 

[Regaj]

@Olle, you can't test the quality of a ground system with a multimeter. If it were that simple, Fluke would never sell any of those multi-thousand dollar meters that were included in that earlier link of yours.

Not that testing individual outlets isn't important - that's in fact what I recommend the OP do. Post haste. Probably using a different electrician, because he's got something seriously amiss out in his garage.

 

[Olle]

@Olle, you can't test the quality of a ground system with a multimeter.

I know. We are not testing ground quality in that picture, but testing for resistance of neutral and grounding conductors since there was no continuity before the repair of our service panel.

This measurement could be a good start if you have the symptoms that OP's system has. Ground quality doesn't help if you don't have sufficient conductivity to your receptacles.