Voltage between breaker box and earth

Question

I recently bought an older (1920) house. The wiring was upgraded ~20 years ago. The breaker box is on the back porch. Circuits run though conduit to the floor of the porch, however the conduit ended there. I've been re running the wires so that conduit goes all the way to the interior of the house.

While doing this I felt a slight tingle (less than a 9v battery on your tongue). When I touched an open blister to the conduit, while lying on my back (sweaty, electrolyte) under the porch. I only felt this when the open blister touched, other parts of my skin did not feel anything. I then put a volt meter on it and read 1v between the conduit and the earth.

There is a grounding wire going to the plumbing. However, the input to the plumbing was at some point changed to Pex, so it no longer has a true grounding path. The meter clearly has a grounding wire going back to the transformer (above ground on a pole that I can visually follow). Is this a problem? Should the breaker box be connected to a grounding stake?

Answer 1

Well, there’s only one source of power there, so if you got shocked at all, it was by 120V.

You still live because the resistances of the available current paths are wildly variable due to all sorts of factors including meteorology. So you got lucky today. Don’t try to get lucky tomorrow; that is to say, don’t count on that high impedance repeating itself.

It sounds like your electrical panel’s Grounding Electrode System relied on a metal water pipe which was improperly changed to plastic without addressing bonding. There might also be other problems with the grounding system or the Neutral-Ground equipotential bond (the connection between N and G in your main panel).

Yes, as George describes, that wire going back to the service pole is neutral, not ground. They are not the same thing. The power company does not supply ground, but they do tie neutral to ground at the pole transformer. This means there are some fault conditions where power will try to return via the earth to that transformer-pole ground. Dirt is an exceedingly poor conductor, so this doesn’t flow a whole lot of current; and since it doesn’t, it creates a voltage gradient along the route. You may have encountered some of that.

Some of your house’s appliances may have a ground fault, but this is not the time to address that; now you want to go over your Grounding Electrode System and your Neutral-Ground equipotential bond with a fine tooth comb to make sure all is in order.

Next, I’d use that voltmeter to make a perfunctory check of all the receptacles in your house (or rather, one per circuit, or rather, one per leg of service if you know what that is. We are looking for voltages that are not 120V, but which add up to 240V-ish. So if one leg is 99V and the other leg is 142V, that’s the red-flag. Further this will change several volts if you turn on a big 120V appliance like a hair dryer or toaster. This would indicate a lost neutral, which means your house is trying to return all imbalance (neutral) current via the Grounding Electrode System. That is easy to fix and it’s almost always in your power company’s bailiwick, so it’s free to you.

Answer 2

Your water pipe would be ok if it had 10’ in contact with earth this is still Legal and code compliant. If you do not have a grounding electrode I would suggest you install a driven rod the easiest way to go 8’ deep and better yet add a second one more than 6’ away from the first. Current code requires a supplemental or 2nd method (2 rods pipes or plates, or 1 ufer + a rod pipe or plate).

If you installed the grounding electrode can you still get shocked with broken skin? YES you can some devices use ground as a return path the amount of current is tiny but when these are present you may not feel it with unbroken dry skin because of your Skin’s resistance. But broken skin has much lower resistance but it is still possible to get a tingle when these devices are used ( normally electronic light controls ).