Thread: Voltage on grounding cable

Hi guys, could someone tell me what concern I should have over finding a couple of volts on the grounding cable attached by the water meter? Thanks Brian

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Volts or amps?

Yes, either way.

If amps, there should be none if everything is okay.

If volts, that means current (amps) is flowing, creating a voltage drop across that conductor - you are measuring that voltage drop, see above statement.

Between what 2 points did you measure the voltage?

Thank you for responding, yes around 1 volt twice lately in older homes. I'm fairly new at this and am not sure how common this is and is it something I should suggest they have an electrician deal with. Thanks again. I'm getting this from my clamp on meter

Brian,

Instead of measuring voltage (which tells you almost nothing without knowing a lot of factors you have no way of knowing), measure current instead.

Use your clamp on ammeter (get one if you do not have one) and measure the current in the grounding conductor. That way you will know precisely what you are measuring, and have a better handle on what that measurement actually means.

Measuring 1 volt does not tell you anything because you do not know the resistance, only that there is 'some current flow because there is some resistance'.

Measuring 1 amp tells you that there is 1 amp flowing through the conductor which *is intended* to have no current flowing through it.

If you are just measuring voltage and do not have, and do not want to get, a clamp on ammeter, then I would stop measuring the voltage, because it is telling you so little, and is telling you nothing that you can determine anything else from, or determine what it means or how bad it is.

So ... ... use a clamp on ammeter (get one if you do not already have one).

Thank you, much appreciated!

Originally Posted by Jerry Peck

Measuring 1 amp tells you that there is 1 amp flowing through the conductor which *is intended* to have no current flowing through it.

Brian,

For comparison purposes, I just went out and measured the current flowing through my grounding electrode conductor where it exists the meter can and enters the conduit protecting it where it goes down the wall and into the ground (just enough space between the meter can and the conduit to get my clamp-on ammeter in there) ... I measured 0.00 amps.

Not bad for a "conductor which *is intended* to have no current flowing through it".

Here,s exactly whats going on, sorry I didn't have my meter with me earlier so I was being vague. Using a Sperry DSA-500 combination volt-ammeter I've gotten gotten readings at the grounding conductor at the water meter, of close to an amp. I said volts earlier, sorry, even in my own house (50 yrs. old) I'm getting .32 when I have the meter clamped around the conductor. I have the meter set on the 40 amp AC setting. This meter is only 6 months old and seems like a fairly decent tool. Thanks

By the way this conductor is coming from the service panel to the piping.

Originally Posted by Brian Robertson

I've gotten gotten readings at the grounding conductor at the water meter, of close to an amp.

Originally Posted by Brian Robertson

By the way this conductor is coming from the service panel to the piping.

Question: Is that conductor "bonding" that water pipe to ground at the panel, or, is that conductor "grounding" the system to that water pipe?

By measuring 1 amp current flow, you are showing that there is a 1 amp ground-fault someplace, or a total of 1 amp of ground-faults in several places.

Depending on what that conductor does (see question above) could give an indication of where (and what) the cause it: service equipment and upstream, or, downstream of the service equipment.

If there is 1 amp on the conductor which is serving as the grounding electrode conductor, and that water pipe is the grounding electrode, then you may simply have a bad neutral connection forcing some current to go through the grounding electrode system back to the transformer (or as complicated as having a bad neutral, especially if underground, nicks in the insulation allow corrosion to start, which eats away at the neutral conductor).

Electrical current not only takes 'the path of least resistance', it 'takes all paths' available to it. If the 'path of least resistance' (the neutral) is a low impedance path as it should be, then you may not be able to measure the current flowing on the grounding electrode system and through earth, because its resistance is much much greater.

If there is 1 amp on the conductor that bonds the pipe to ground, then you have 1 amp flowing on that pipe ... from somewhere. Use your voltage sniffer to check for 'live' plumbing fixtures, you may find one, and somewhere around there may be a conductor being crushed against a pipe, causing electrical leakage to the pipe. Or maybe just a damaged wire with the insulation cracked, missing, etc.

I remember that I would occasionally find energized cast iron drain piping in crawlspaces under older homes, something, somewhere, was energizing it. Besides, isn't a cast iron drain system an "interior metal water piping system"? Thus, it requires bonding to ground.

I agree with Jerry P. there is something wrong. One of the most common faults is at the water heater, if electric. Try turning appliances off one at a time while monitoring the current on the ground conductor.

Thank you, I really appreciate the response, but of course I have another question . It is a GEC from the panel so you state it could be just a "bad neutral connection somewhere". It is overhead service and all seems well to the panel. So I'm not sure what examples of a bad neutral connection are that would cause that current to flow. Could you give me a couple examples of what this might be. Thanks again Brian

Vern, thank you, I was reading Jerry's post and replying, I will try the appliance shutoff thing. Now would I just need to shut them off or unplug as well? I love this site!!!

Originally Posted by Brian Robertson

I will try the appliance shutoff thing. Now would I just need to shut them off or unplug as well?

Brian,

In most cases, just shut turn them off (if there is a bad neutral/neutral connection problem). In this case, no need to address 240 volt appliances, they do not cause problems when there is a bad neutral.

However, if you are looking for ground faults, disconnect/unplug them. In this case, you can have ground faults in 240 volt appliances.

Here are two examples of bad neutrals: 1) neutral conductor making poor connection in neutral terminal causing high resistance - usually you can see evidence of this at the terminal or in the insulation of that neutral near that terminal; 2) overhead service neutral/hot leaking through to each other, causing the conductor to corrode, causing higher resistance.

If you increase the resistance in the neutral conductor, it become closer to the resistance of the earth ground back to the transformer. If the neutral conductor resistance increases enough (so the resistance of both paths are the same) the same amount of current will flow through the ground path as through the neutral path.

Increase the resistance of the neutral conductor to its maximum (cut it) and all of the neutral current will through the ground conductor, but that creates its own problems because it is now a higher resistance path back to the transformer, among other problems. Which is why it is "not intended to" have current on it.

Hi Jerry, Ok, I have a lot better idea of what's going on and what I might be looking for. Thanks again for the answers and your time.

This is my record so far on a water line. The problem with finding this condition is that most likely it will not be corrected. I just did a re-inspection for this condition last week. The electrician, ComEd and the village inspector were all at the home on repeated visits and came to the conclusion all was corrected. I still found 4 amps.

I have talked to many people about amperage on water lines and have come to the conclusion that most electricians and inspectors do not understand what is going on and that incorrect info is rampant.

Eric,

That, 11 amps, is A LOT.

The first thing, and simplest thing, to do is to monitor the ammeter while flipping breakers off. With each breaker that makes a difference, put a piece of painter tape next to it and write down the difference it made.

There may be a multitude of problems on several circuits, or just one circuit, in which case the correction is easy - trace that one circuit out and find and fix the problem.

If all breakers effect the reading, I would start looking at what is common to all circuits, such as the neutral and its connections.

Don't forget, older ranges and dryers had the neutral serving as the grounding conductor.

ONE amp? That's not much .... especially considering the resolution of the meter. You're in a position where you're trying to measure ounces with a gallon jug.

More to the point, there may not be a problem at all. Electricity takes ALL paths, so some current will travel through the ground rod, the water piping, and every other ground, as well as taking the PoCo neutral back to the transformer.

To trace down the problem requires more time, and expertise, than even the ordinary sparky. It could be a utility problem, a problem with a neighbors' house, etc ..... or no problem at all. Though it might be a clue that you inspect the service drop for squirrels nibbling on the bare neutral.