Ground pooping out? Add a grounding rod?

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Old 08-30-18, 04:18 PM
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Ground pooping out? Add a grounding rod?

Thanks all for any advice.

I have an electric car that I want to charge off my 110V service in my detached garage. Single run (hot, neutral,ground) from my box ~100ft to my detached garage (main panel to plug - the underground part is ~40ft). The car's charger tests the ground before charging and the outlets out there (tried all 4) all fail the ground test almost every time. I should note that it passed the test once, but I haven't been able to replicate that. I'm assuming that the smallish-gauge grounding wire (14, I think) is the culprit and the impedance is too high, just barely. Can I just add a grounding rod at the garage and wire it to the ground in the junction box out there? No separate panel.
 
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Old 08-30-18, 04:32 PM
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Can I just add a grounding rod at the garage and wire it to the ground in the junction box
No. You must have a low resistance ground path from panel to garage. That requires a wire. Is the garage powered by a cable or conduit. If cable what kind. I
 
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Old 08-30-18, 06:31 PM
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If the ground is #14...... what size are the hot and neutral wires ?
That charger is only testing the ground for safety. They would not be running a high test current thru it. So either the charger is starving for power or that ground is not solid back to the panel.
 
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Old 08-30-18, 06:34 PM
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How many amperes does the car charger use?

At 15 amps 100 feet away using 14 gauge wire, the charger will suffer 6% or about 7-1/2 volts of drop. This is twice what is considered good taste in circuit design.

Your charger may or may not work at 6% drop but if it did it would take much longer than expected to charge the car.

The only way you can control the current draw is if the charger has low, medium and high settings and then you can set it to low and see if the current draw becomes small enough for your system to support.
 
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Old 09-03-18, 07:15 AM
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Thanks all for your comments. The garage had 12 gauge 110V service including a ground wire (presumed 14G, but whatever is standard in a 12/2 cable most likely) going all the way back to the box. An electrician installed the plugs that I'm using, and an outlet tester shows that it is wired correctly including a functioning ground. It's a GFCI receptacle and a test trips the box, so I assume that the ground works somewhat. The car also charged once (it never worked again), drew 12A with no problem and minimal voltage loss. My guess is that the resistance its seeing is too high as it's giving a fault that states "ground loss, the mobile connector detects a loss of ground." I'm a bit surprised, to be honest.

When I talk about adding a grounding rod, I mean supplementing the ground wire going back to the main breaker box with a grounding rod out at the garage, which should substantially reduce the impedance/resistance. There is no breaker box at the garage.

To answer you each directly:
Ray: Yes, there is a ground back to the house, but the fault still seems to be triggered (almost every time, though once it was satisfied and charged). It's a cable, I believe the electrician said it was 12 gauge. An outlet tester shows proper wiring, including ground. I was just guessing that the car's charger wasn't happy with the resistance as it is a long homerun, but there is a ground that is working, at least as evidenced by the outlet tester and the GFCI triggering normally - as well as being able to charge once.

PJmax: 12 gauge hots and whatever ground is standard in that cable (14?)

AllanJ; The hots are 12G, I'm guessing that the neutral is 14G. The car did manage to charge once with minimal voltage loss, it can be set as low as 8 Amps but I don't get the chance to even try as the charger itself rejects the outlet, showing the fault above (ground loss).

Quick question for all: Is there a way to measure the ground resistance?
 

Last edited by summerrain222; 09-03-18 at 08:27 AM.
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Old 09-03-18, 09:01 AM
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12 gauge hots and whatever ground is standard in that cable (14?)
If it is a cable all the wires will be the same size in most cases unless the cable is very old.

My guess is that the resistance its seeing is too high
Resistance of #14 wire is 2.525 ohms and #12 is 1.588 ohms at 1000 feet. So at 100 feet it will be .252 and .1588 respectively. Resistance of the wire is not your issue if the wire is not damaged and connections on each end are good.

The ground has no function of a circuit except safety to carry fault current to trip a breaker or blow a fuse. I believe your issue is likely voltage drop and your charger is very sensitive to it. A ground rod will likely not be any help as the ground has much more resistance then a copper wire.

I would recommend checking both ends of the cable and make your the connections are good and tight. You could try installing a ground rod, but I doubt it will help any. (Stranger things can happen) I would get a 100'+ roll of 12/2 cable and run it to the garage temporarily and see if that fixes the issue.
 
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Old 09-03-18, 10:49 AM
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Charging an electric car on a 120v 20A circuit will take a long time.
Most electric cars use a 30-50A 240v circuit for charging.
 
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Old 09-03-18, 11:20 AM
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Originally Posted by summerrain222
I have an electric car that I want to charge off my 110V service in my detached garage.
Detached garage?
Probably has GFCI breaker or outlets.
-GFCI outlets HATE battery chargers.


Eh, unless that car says "Barbie" or "Tonka" on the hood, it is going to take a LONG time to charge on a 120v 15A circuit that is far away from the breaker box. And I'd expect the circuit to trip easily, as in,
"charger" + "garage door opener"
"charger" + "garage fridge compressor"
"charger" + "power tool"
 
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Old 09-03-18, 10:36 PM
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Thanks for the input all. The charger is very specific about why it is refusing to charge, the problem is identified as ground loss, not voltage drop which has it's own error code. GFCI outlets can be a problem, yes, but as I understand it only by tripping during the ground test that EVs do prior to charging, which hasn't been a problem. The garage is basically a parking spot, no other electricity use out there except for an LED lightbulb. For those concerned about slow EV charging, my commute is 2 miles and I can charge at work, so the blanket understanding that Level 2 charging is needed overlooks many use cases where that is not the case. Level 1 is sufficient for my needs, especially as the only real reason I truly NEED it is battery protection in the dead of winter, otherwise it's just convenience charging.

I guess it's still a mystery exactly what is going on here. I'll try another charger to make sure that's not the problem (they cost $300 so it'll be a pain to find one). I know that the ground isn't severed as the car charged once, that means it was able to pass the grounding test once, I was guessing that if the ground is sketchy but intact the small impedance fluctuations due to weather or pure luck might be the straw that broke the camel's back. I'll be calling an electrician to try to troubleshoot what's wrong with the ground. I like the run-a-fresh-temporary-cable-for-diagnostics idea. Maybe try a temporary non-GFCI to isolate that. I think I might try the new grounding rod idea too. It seems safe, to be sure. Does anyone know if it's code compliant? Thanks all.
 
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Old 09-04-18, 12:51 AM
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I might try the new grounding rod idea too. It seems safe, to be sure. Does anyone know if it's code compliant?
No, as I already wrote in my first post it is not code compliant.
 
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Old 09-04-18, 07:49 AM
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Thanks. I was a little unclear if you meant that it was not code compliant to use a grounding rod at the garage in lieu of a grounding wire back to the box, which is not what I was proposing but I thought you were referring to, vs not code compliant to have both a local rod and a ground wire back to the main panel (like when there's a subpanel at the garage, which is grounded with a grounding rod at the garage as well as a grounding wire back to the main panel).
 
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Old 09-04-18, 11:58 AM
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I guess it's still a mystery exactly what is going on here.
It is apparently a break in the ground line between that receptacle and the panel.
 
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Old 09-04-18, 02:25 PM
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I believe a ground rod at the detached location AND a grounding conductor back the main panel are required:


NEC 2014 - 250.32(A)

Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
 
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Old 09-04-18, 06:35 PM
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A ground rod and wire will likely only cost you $20. Might as well give it a shot.
 
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Old 09-05-18, 08:50 PM
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Exception: A grounding electrode shall not be required where only a
single branch circuit, including a multiwire branch circuit, supplies the
building or structure and the branch circuit includes an equipment
grounding conductor for grounding the normally non–current-carrying
metal parts of equipment.
 
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Old 09-09-18, 03:31 AM
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Thanks, sounds like the second grounding rod is legal, but not required. The electrician gets here tomorrow, always helps to know what I'm asking for beforehand.
 
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Old 09-09-18, 03:34 AM
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"I guess it's still a mystery exactly what is going on here."

"It is apparently a break in the ground line between that receptacle and the panel."

Exactly, I'm confused too. The car charged once, so the ground wire going back to the main circuit breaker has to be intact, but it has otherwise failed every time, showing a "ground loss." The time it worked was after several fails, and the car won't charge without confirming a functioning ground. I don't know what to make of that. I'm just guessing that the impedance is close to the threshold for what the car will accept, hence my interest in a local grounding rod.
 
 

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