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Old 08-24-2010, 06:56 PM   #1
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Help Needed with Open Ground


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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Old 08-24-2010, 07:05 PM   #2
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Help Needed with Open Ground


By the way - the test button on the GFCI is working, so it is 'protected'. Only problem with it (and it's a big problem to me) is the open ground situation.

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Old 08-24-2010, 07:22 PM   #3
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Help Needed with Open Ground


neutral should be tied to ground at the breaker box... so you should be able to do a resistance check and read 0-ohm from neutral to ground.
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Old 08-24-2010, 07:28 PM   #4
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Help Needed with Open Ground


Thanks johnnyboy, but I'm not understanding. What exactly should I do with that information?
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Old 08-24-2010, 07:56 PM   #5
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Help Needed with Open Ground


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Originally Posted by mark2741 View Post
Thanks johnnyboy, but I'm not understanding. What exactly should I do with that information?
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.
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Old 08-24-2010, 08:51 PM   #6
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Help Needed with Open Ground


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.
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Old 08-24-2010, 09:43 PM   #7
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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.
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

Last edited by mark2741; 08-24-2010 at 09:45 PM. Reason: add voltage readings
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Old 08-24-2010, 10:41 PM   #8
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Help Needed with Open Ground


If the GFCI is the last receptacle on the circuit, perhaps the problem is with the ground wire connection upstream somewhere.

An open ground in a GFCI is not a problem for most purposes, but it should be labeled "no equipment ground."

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Old 08-25-2010, 08:24 AM   #9
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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.
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Last edited by AllanJ; 08-25-2010 at 08:32 AM.
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Old 08-25-2010, 08:40 AM   #10
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Help Needed with Open Ground


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.
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Old 08-25-2010, 06:42 PM   #11
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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.
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Old 08-26-2010, 06:59 AM   #12
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Help Needed with Open Ground


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.
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Old 08-26-2010, 08:05 AM   #13
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Help Needed with Open Ground


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Originally Posted by mark2741 View Post
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.
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.

Last edited by a7ecorsair; 08-26-2010 at 08:09 AM.
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Old 08-26-2010, 09:17 AM   #14
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Help Needed with Open Ground


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 ??
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Old 08-26-2010, 09:30 AM   #15
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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 ??
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.

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