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Help Needed with Open Ground

10K views 35 replies 11 participants last post by  Jim Port 
#1 ·
Bought a new (used actually, built in 1959) house. Most of the electrical has been upgraded throughout the house over the past 10 to 20 years.

When the inspector came through he said that a large number of receptacles in the house were testing as having reverse polarity. I got a credit back at settlement and then proceeded to troubleshoot myself when I moved in. All of those receptacles (about 9 of them) were simply wired reverse, so it was a relatively easy fix. In the one hallway bathroom, there was a GFCI that was testing 'reverse polarity' (using one of those little gfci testers you buy for $10 at HD). Since it was the wrong color (an old tan one, while everything else was new and white), I replaced it with a new gfci. The reverse polarity went away, but now the tester is saying there is an 'open ground' on the circuit.

At first, I took my multimeter and measured all of the receptacles on the entire circuit (5 of them, including the gfci in the bathroom). This particular 15a circuit powers both this small hall bathroom and two small bedrooms. I measured ~120v, as expected, when measuring from HOT to Ground in each receptacle. And, as expected, I measured 0v when measuring from neutral to ground. That tells me that those receptacles are wired correctly (I think). A friend told me I needed to physically check each receptacle/fixture on the same circuit as the gfci, so I did. They were all wired correctly. Keep in mind that this gfci is not protecting any other receptacles. It's the only receptacle in that bathroom.

Left is a few light fixtures and a ceiling fan. Those too are all grounded properly.

I'm not very knowledgeable on electrical work but I know how to use a meter and hook up receptacles, switches, etc. I'm not sure what else to do. Could it be that I bought a bad GFCI? My lack of experience makes me doubt that I just simply have bad luck! But I double-checked the gfci to make sure I wired it up correctly. I followed the directions (line vs load), and it's grounded both at the box and the gfci itself. I did measure the voltage from hot to ground in the gfci too and it is measuring 0, so it's not my cheap tester. It definitely is not grounding properly.

I'm assuming that, since everything else IS grounding properly when measured, that it wouldn't be a junction box in the attic (if there is one - I didn't see any but it's possible as I haven't been up there much since moving in). Same for the circuit breaker/panel itself. I had my brother look at it when I first moved in (he's a commercial electrician) and he said the ground wire was hooked up at the panel, and to check all the receptacles/fixtures for a loose ground wire. No luck.

Any ideas?
 
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#5 ·
So far, you've measured 0 VOLTS between neutral and ground. This doesn't actually tell you anything. You can measure 0 VOLTS between the Neutral and free space.

What you need to test is that there is acutally 0 OHMS between the neutral and the ground. This means that the neutral and ground are connected to each other at the main disconnect.

If you measure significant resistance between the ground and the neutral, it means that something is awry somewhere. If the house was built in 1959, it probably doesn't have grounded wire everywhere. SO, if someone extended a circuit to provide the GFCI you're testing.... there could be a ground wire from the GFCI to the original outlet, but no ground provided to the original outlet.

Not sure if that makes sense or not. Hope it did.
 
#6 ·
After verifying that you get 120 volts hot to neutral, you can verify that the ground is connected by getting 120 volts from hot to ground.

This is an alternative to getting continuity or getting zero ohms between neutral and ground.

When using your meter on the ohms setting, be sure the power is off in the circuit being measured.
 
#7 · (Edited)
Thanks everyone. As I said - I did measure all of the receptacles in the circuit, one by one, between hot and ground. I got the expected ~120v for each. That tells me that the electricity is flowing from hot to ground, so there has to be flow to ground, right? Wouldn't measuring the resistance from neutral to ground would just be a duplication of this confirmation, right?

Each outlet is operating as one would expect, per the measurements:

Hot to ground = ~120v
Neutral to Hot = ~120v
Neutral to Ground = 0v
 
#9 · (Edited)
Under normal conditions current should not actually be flowing between hot and ground. A situation where current is flowing where it should not be is called a fault.

But a surer test of the quality of the ground connection back to the panel is to connect a 100 watt incandescent light between hot and ground for a few seconds or minutes. (Probably most easily done using short jumper wires with alligator clips on the ends.) Measure the voltage while the light is lit, you should get almost the same 120 volts. Significantly less voltage when the light is switched on means you do have a problem in the overall ground connection (aka bonding) back to the panel (or possibly in the hot connection). (Hardly anyone bothers to conduct this quality test using many amperes.) The sheath of BX cable and as few similar spiral flexible conduits is nowadays not considered an adequate ground. More modern prewired flexible cables may have a straight metal strip or ground wire going through.

While we are on the subject of testing, grounds and neutrals should not be tied together (bonded) anywhere except at the main panel. To prove this, if you unhook the neutral from the terminal strip (or bus bar) in the panel (keep power off during this exercise), you should measure no continuity (or nearly infinite ohms) between neutral and ground up at your receptacles on that particular circuit.
 
#10 ·
allan gave a good test. for a meter test, do this.

remove power.
remove gfci and make sure all wires are pulled out and not touching. using the volt function make sure zero voltage is on any wire with respect to a bare wire or metal box. for this test you may want to place your second lead on a nearby outlet "ground" that you have tesed good.
place your meter in ohms function and read from neutral to ground wires, it should be a few ohms. do not put your body in the meter circuit, you can squeeze one test lead and a wire together with one hand, but not both hands.
is there more than one romex coming into box? if so you can determine which romex coming in is the feed by applying power and (CAREFULLY)testing for 120v. the feed is the ground you need to test here.
 
#11 ·
Tim - wish I had read your post before giving up for today : (

I went through all the wiring on the circuit again and still no luck. I did, with the power off, measure resistance between neutral and ground. It came back as 'open'/infinite on my meter. So there is definitely an open in the ground I guess?

Problem is, I have no idea where it could be. The GFCI is not protecting anything. There's only one set of wires coming into that receptacle box and the gfci receptacle is wired correctly. I looked up in the attic to see if there was a junction box up there (as the romex feeding the gfci appears to be coming from the attic), but if there is it's under a ton of blown-in insulation and there is no plywood to make it possible for me to walk around up there to look for it.

I have experienced no problems whatsoever and, as I said before, the gfci trips as expected when the test button is pressed. At this point I give up. I'm just gonna stick the 'no equipment ground' sticker on it and walk away with my tail between my legs : (

I'm bummed I couldn't find the problem.
 
#13 · (Edited)
I have experienced no problems whatsoever and, as I said before, the gfci trips as expected when the test button is pressed. At this point I give up. I'm just gonna stick the 'no equipment ground' sticker on it and walk away with my tail between my legs : (

I'm bummed I couldn't find the problem.
Oh come on, don't give up quite yet.:no:
It looks like you have identified all the devices in the circuit. Have you pulled each one out and checked that all the ground wires are physically connected and that all cables entering a box each have a ground wire.
Remove one of the receptacles that appears to be in the middle and remove it. Turn the breaker on and check which outlets are still live. Hopefully the GFIC and one or two others will be dead. If not, try another combination until your GFIC is dead along with one or two others.
Once you get this narrowed down to two or three, remove those devices. Turn the breaker on and locate the live wires, one pair will be hot. Wire nut it so you know which one it is. Turn the breaker off.
You can now check continuity between those empty boxes by connecting the black and ground out of the same cable and then going to another empty box and measure for continuity from black to ground. Do this with the breaker off.
This will map out the circuit and help narrow down the open ground.
 
#12 ·
mark, there must be a box before this one that loses the ground. depending on one story or two, look in basement or attic in the vacinity. look on the other side of the same wall. i usually turn off the breaker and test everything (lights &receptacles) for operation, what doesn't work is on that branch circuit. then test it out.
 
#14 ·
If your testing 120 volts hot to ground at the gfci you most likely have a good ground. Have you tested from the green screw of the gfci to the ground prong hole for continuity?

Reversed polarity prevents the gfci tester from detecting an open ground... once that is corrected it can then check between hot and ground.

You do have a ground connection to the green screw on the gfci ??
 
#15 ·
Yes.

Here's what I've done so far:

1. Physically pulled out and checked all receptacles, fixtures, and switches on the circuit for proper wiring, including ensuring that all grounds are attached securely. They all are.

2. Tested all receptacles on the circuit with my multimeter. Each of them shows:
Hot to Ground: 120v
Neutral to Ground: 0v
Hot to Neutral: 120v
...as expected.

3. The gfci that is showing open ground measures:
Hot to Ground: 0v
Neutral to Ground: 0v
Hot to Neutral: 120v

4. With power off to the circuit, I tested the gfci again, this time for resistance as suggested:
Ohms between Neutral and Ground: infinite

That tells me there is an open somewhere. I don't remember for sure but I do recall doing something that told me the gfci itself was fine. That said, tonight when I get home I will pull the gfci out of the box and measure voltage from the hot to ground, this time with the probe on the ground screw and not the ground plug in the receptacle. If that measures 0v as expected, then we know it's a good gfci and the problem is in the line somewhere.

The GFCI is at the end of the circuit. That is what is so perplexing about this. It doesn't feed or protect anything else. Everything that I can get to appears wired correctly. I'm assuming now that the open ground is in a junction box in the attic, and there's no reasonable way for me to get to that because, as I said before, if it's up there it's underneath blown-in insultation and I have no plywood up there to get to it easily.

The GFCI looks like it is fed from a light fixture that sits over top of a medicine cabinet, about 2 feet above it.
 
#16 ·
The GFCI looks like it is fed from a light fixture that sits over top of a medicine cabinet, about 2 feet above it
.

Good place to check if it is on the same Circuit.

I understand better now what you have going on. I thought you were getting 120 volts to ground at the gfci. Think of the ground and neutral as parallel paths back to the panel neutral bar where they are then joined. The neutral is a current carrying wire for completing the circuit for 120 volt loads. The ground wire (EGC) is a bonding path to connect all metal together so in the event of a ground fault it will conduct fault current back to the transformer and cause a breaker to trip out. Like the diagrams I have at the end of this post.

It does sound like you have an open ground. But a gfci will protect you from electrocution but not shock. Which means if you have a ground fault and no equipment ground or an open equipment ground the leakage current out to your body if you come in contact with the fault will cause the gfci to trip...you may feel a slight shock before it trips. If the ground is present then the fault current travels the ground back to the panel and then to the transformer causing the circuit breaker to trip and clearing the fault. until that is corrected the breaker will not reset.

Anyway you are just going to have to divide and conquer till you find the open.
 

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#17 ·
Thanks Stubby.

I'll keep at it. Now that I've gone through all the reachable spots (receptacles. light fixtures, switches) and checked that they were all wired correctly, it's time to just as you said - divide/isolate.

I'm gonna start tonight with pulling the gfci out from the wall and measuring the voltage from the ground screw to hot (that way I'll know for sure it's not just a bad gfci (if it is, I'll be p*ssed!!)). While that's out, I'm going to turn the circuit breaker off, pull the light fixture that I *think* feeds the gfci, and measure the resistance from ground there to the ground on the gfci. That will tell me if the ground is connected between them. Then go from there.

I had given up, but now that all of the likely/probable situations are confirmed fine, it's just a matter of isolating with my meter using the resistance measurements, correct? Just measuring from one ground point to the next, right?

I never had any electrical training but back when I was in the Navy I went through some electronics schools. I did very poorly in them - just enough to fake my way through (I was young and didn't have much interest). So I know enough not to get myself killed/injured, and how to use test equipment safely - that's about it : ) Working with electronic circuits I always used an oscope to trace things out. Much easier when you can see the entire circuit (soldered to a board/boards) than trying ti visualize things through walls! : (

I'll post my results.
 
#18 ·
I never had any electrical training but back when I was in the Navy I went through some electronics schools. I did very poorly in them - just enough to fake my way through (I was young and didn't have much interest). So I know enough not to get myself killed/injured, and how to use test equipment safely - that's about it : ) Working with electronic circuits I always used an oscope to trace things out. Much easier when you can see the entire circuit (soldered to a board/boards) than trying ti visualize things through walls! : (

I'll post my results.
Oh, another Navy guy:thumbup: What school/rating did you get your electronics in?
 
#20 · (Edited)
Update:

I turned off the circuit breaker and pulled the GFCI again. Measured voltage between the ground screw and the hot and got 0 volts, so I know it's not the GFCI itself at fault. Also did some measurements between the ground wire connected to the GFCI and some grounds in the two fixtures in that bathroom (a light fixture and a rocker switch). Infinite ohms. Those two fixtures are not connected directly to the GFCI (though they are on the same circuit).

I am pretty certain, based on the romex connected to the gfci coming from the direction of the ceiling, that the open ground is either hidden behind the bathroom wall and in the romex wire sheathing itself (very doubtful), or is in a junction box in the attic which is only about 5 feet above where the GFCI is located (in a 2nd floor center-hall bathroom). As I said before - that attic has blown in insulation and no flooring. I looked up there with my flashlight and I don't see anything - no electrical wiring at all, so my guess is that the junction box is buried somewhere under that insulation, above the bathroom.

I'm not optimistic. I may just wait until the fall/winter, when it's not boiling hot in that attic, and see about trying to get a narrowed piece of plywood up there. The two attic accesses are too small to fit two large sheets of plywood up there in order to alternate 'sliding' them one at a time towards where the junction might be.

I'm guessing there is no other way to isolate this than to physically try to slide my fat a** across the joists of that hot attic?
 
#21 · (Edited)
when checking upstream junctions for your ground integrity, don't assume that wires in a wire nut are connected electrically. they need to be checked. fyi there should not be any junction boxes behind wall coverings.

the gfci functions by watching for current to take a path other than the standard neutral return path.
 
#22 ·
Thanks Tim.

I just wish I could get to the next point upstream : (

That's the problem at this point. I am pretty certain that that's where the problem is, but I can't get to it. And due to it likely being buried under lots of blown-in insulation, on the opposite side of where the small attic access is, I am not even positive it's up there. I'm just assuming it is.
 
#23 ·
If you could get access to a toner, commonly called a fox and hound, you could place a tone over the ground and trace it behind the drywall. When the tone stops you have your open.

Gardner-Bender has a wire tracer for about $40 that I have used. IIRC it was called the lan tracker.
 
#24 ·
Thanks Jim - I was wondering about this. I used tone/signal generators when I was in those Naval schools : ) In fact, I thought about how useful that would be in this application, so I looked at some tone generators at HD the other day and wondered why they couldn't be used in electrical wiring. They were all labeled for use with telephone and cat 5 wire and they made no mention of being used for residential wiring so I was hesitant to plunk down the cash for one. They had one for $30 to $40. I think I might give it a try and return it if it doesn't work.

If I recall correctly, it's simply a matter of cutting the power to the circuit, inserting the signal (if I recall correctly, the ones I saw had alligator clip probes, so I guess I'd have to pull the gfci yet again!), then trace out with the sniffer/listener device?
 
#25 ·
Yes, the power needs to be off when testing. You can clip the alligator clips to the ends of the wires. Since I do this more often I made up a cord cap with short lengths of wire sticking out to make it easy to clip on to.

Funny that you said you used to work around the Aegis system. In another life I used to draw the illustrations in the tech manuals.
 
#26 ·
An update....no good news....

Yesterday I bought a tone and probe kit (a Fluke Pro3000 for $69 from HD). Cut power, hooked up the tone generator to the hot/neutral that were previously hooked up to the gfci, did a quick test to trace where the wire went behind the wall once it leaves the gfci box. It goes up then to the wall to the left, with the signal still strong at the ceiling. So I figure it's definitely in the attic.

Fortunately, after thinking before that there was no way back there to that spot in the attic, I remembered that there are 2 attic accesses (there was an extension added to this house many years ago). The extension attic is floored and lighted, and a previous owner broke through the drywall to get to the main attic. So today I was able to rig an extension light through, and there were a number of thin boards for me to crawl/slide over to the vicinity of where the wires would have come through the ceiling and presumably up to the attic. I placed the tone probe everywhere I thought and couldn't get a signal anywhere. I dug around a lot but there's so much blown-in insulation, which is then over top of regular bat insulation, and a lot of the wiring is under that I think. I eventually found a junction box that was under insulation, waved my tone probe over top of the wires going into it and got a *very* slight signal. But by that time the walls were closing in on me and, with it being at least 120 degrees up there, and no one home other than me (in case I wind up killing myself with electricity), I gave up. The signal was SO much slighter than the signal I was getting while probing through the wall down in the bathroom where the GFCI is, that I doubt that's it. But it's the only signal I could get.

I may try again tomorrow morning, when it's not so hot up in the attic. But I'm not hopeful. I'm seriously considering just leaving the open ground.
 
#30 ·
Thanks oleguy. That makes sense, but I just assumed that since the hot and neutral would be in the same cable/sheathing as the ground, it would work just as well. I was tracing it back to the junction before the GFCI, which is up in the attic I believe, underneath insulation.
 
#28 · (Edited)
Good grounds are called upon to carry current.
You can expect the voltage on ground to rise up to 3 vac or so when passing 10 A through it. Measuring voltage is half the story.

You can check this ground impedance with a hair dryer or toaster or
buy Ideal's 65-165 tester. Just reading the instruction manual for this thing is an education unto itself.

I don't have a financial interest in Ideal's products.
 
#29 ·
??

I'm not sure I'm following you. I know I definitely have an open ground in the circuit. I am 99% sure it is in the junction/connection that is just before this GFCI. I am 99% sure that this junction/connection is somewhere in my attic, underneath insulation.

How would measuring impedance help me find the open ground?
 
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