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Chevy Volt charger is ground faulting but tests on Duplex seem fine.

Chevy Volt charger is ground faulting but tests on Duplex seem fine.

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  #1  
Old 11-04-12, 09:32 PM
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Chevy Volt charger is ground faulting but tests on Duplex seem fine.

Hello,

I have a new 120 V AC charger for a Chevy Volt that has been engineered to sense good ground before it allows usage. The electrical problem is that there seems to be voltage between neutral and ground on the circuit I want to use in my garage. It is not enough to fault the charger immediately but is enough to fault it about 15 minutes of use.

Multimeter test show when there is no load on the duplex there is 121 V AC between Hot and Neutral. Also 121 V AC between Hot and Ground. A few millivolts exist between Neutral and Ground.

However, when I plug in the charger, I now have 121 V AC between Hot and Neutral. 112 V AC between Hot and Ground, and 9 Volts AC between Neutral and Ground.

Same device plugged into another part of my house shows 121 between Hot and Neutral, 121 between Hot and Ground, and does NOT show voltage between Neutral and Ground. So my thought is I have a bad duplex and need to change it. I decided to use a GFI as the replacement since the location could become wet. However, even with this new GFI I still see the voltage discrepancies in my garage but only with the charger plugged in.

I am not sure what to do know since my no load voltages seem fine and I have changed duplexes, Hot and Neutral wire feeds, and new ground to the box.

Not sure what to do next but I am pretty sure that this difference in voltage potential on the Neutral - Ground is causing my charger to fault.

Thanks.

P
 
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  #2  
Old 11-04-12, 09:42 PM
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However, when I plug in the charger, I now have 121 V AC between Hot and Neutral. 112 V AC between Hot and Ground, and 9 Volts AC between Neutral and Ground.
You should never read voltage between neutral and ground. Both should be at the same potential. You have a problem with the ground to that outlet. Changing the receptacle will not correct the problem.
 
  #3  
Old 11-05-12, 03:45 AM
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Agreed. I am chasing my tail though since I have proper balenced potential voltage between hot/ground, hot/neutral and no voltage between neutral /ground until I plug in a device. How do you chase down a grounding issue when it doesn't show up until after the load is applied?

Thanks.
 
  #4  
Old 11-05-12, 04:22 AM
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Sometimes it is best to just start from scratch rather the try to find an elusive problem. A lot less frustrating and much quicker. Assuming this is an attached garage I would run a new dedicated circuit. Under current code it would have to be GFCI protected in a garage.
 
  #5  
Old 11-05-12, 04:43 AM
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If you are using a digital multi-meter stray voltage could affect it.

One of these may help:

Click image:

Image courtesy of homedepot.com
 
  #6  
Old 11-05-12, 06:10 AM
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Hello Ray and Greg,

Yes, I have a dedicated 20 amp line to the duplex. I also used the wiring tester you show after I completed all my connections. I always do. Yet the tester shows normal, correct wiring.

I have tested both a regular duplex and a GFCI. With no load, both show proper voltage ratios from ground to hot to neutral. Both show proper test lights using the wiring tester. With the charger attached, both show 9 volts on neutral to ground.

Still scratching my head.
 
  #7  
Old 11-05-12, 06:50 AM
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Preform the ground to neutral with an analog multimeter and a load such as a lamp or heater plugged in. I suspect a breakdown of the cable insulation under load is the problem. No load you don't see it. I suggested just running a new circuit in my previous reply since it is unlikely you can find or fix a problem with the cable.
 
  #8  
Old 11-05-12, 06:51 AM
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Sounds like you've got a floating ground. Double check its connection in the panel.
 
  #9  
Old 11-05-12, 07:13 AM
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Hi Ray and Astuff,

Yes, I checked the connection at the panel and it shows proper voltage ratios.

Just for the hell of it, there are two dead lines in the quad box from an old 3 way switch. Since they are no longer used, I decided to try them as "new feeds" to the duplex. I still have the problem. It seems unlikely to have multple bad lines. Hmmm.

The problem is troubling for sure and I have spent waaaaaay too much time troubleshooting. Interesting comment about the load/no load and insulation breakdown. I have never had to put a "sensitive" electronic component on this line in the past so I never saw the problem. Saws, drills, sanders, etc must be much more forgiving of this condition even though it is not safe.

I think I am forced to pull new #12 lines.

I'll update the list later today. Thanks for the suggestions!

Paul
 
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Old 11-05-12, 07:19 AM
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Please understand no guarantee I am correct. Actually I would have suspected the charger if you hadn't written:
Same device plugged into another part of my house shows 121 between Hot and Neutral, 121 between Hot and Ground, and does NOT show voltage between Neutral and Ground.
 
  #11  
Old 11-05-12, 07:36 AM
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Since you are in "IL" you don't happen to be in Chicago and have this in conduit that is used for the EGC?
 
  #12  
Old 11-05-12, 07:45 AM
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Hi Ray,

Yup. Me too which is why I did the test. In fact, I am running a 12 gauge extension cord from inside the house to the charger in the garage for overnight charging of the car. Works fine on the inside the house circuit.

And yes Astuff, I am in Cook County, IL ...not Chicago and the conduit is the ground. In fact, the conduit is buried in the slab of the garage floor from an addition done years before I owned the house.

Paul
 
  #13  
Old 11-05-12, 07:51 AM
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Then the conduit is broken some where. May be just not tightened enough but difficult to find. Just run a 12 gauge green back to the panel. You will need to bond to the box.
 
  #14  
Old 11-05-12, 07:57 AM
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Great idea!

I think I'll test that theory external to the pipe before I pull more wire. Should be easy enough to do.

Thanks.

Paul
 
  #15  
Old 11-05-12, 05:45 PM
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Hello again,

With the duplex removed from the box, I ran a ground directly to the duplex terminal. I energized the circuit and measured something different.

First, at the load center breaker I see 120 V AC from hot to neutral.
At the duplex I read 111 V AC across hot to neutral and 6 V AC across the new ground to neutral with no load.

it seems that there is something going on inside the pipe that must be corrected. I think I am back to Ray's suggestion of pulling all new wire and probably a dedicated ground while I'm at it just to cover all the bases.

thanks for all the ideas.

Paul
 
  #16  
Old 11-05-12, 06:32 PM
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when I plug in the charger, I now have 121 V AC between Hot and Neutral. 112 V AC between Hot and Ground,
This one statement tells me you have a ground problem.
 
  #17  
Old 11-06-12, 03:36 PM
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Hello again.

Success!!

I pulled all new ground, neutral and hot back to the load center. Why not. I then methodically tested each point in the installation looking for voltage leaks. Good to go.

Final test was to plug in the charger and see if it faulted. All green lights!

Thanks very much for your advice. It took a while to sort out but such is the DIY project.

Regards,

Paul
 
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