House wiring issue

[Hondaman]

Okay, this is complicated. My house (built in 1964) is mostly wired with 12-gauge copper, 2-wires. But the outlets are 3-prong, and the ground prong on the receptacles is not hooked up to anything. There is about 10-12 volts between hot and the ground prong. Why?

One room of the house has outlets that are protected by a GFCI in the circuit breaker box. When I place a voltmeter between hot and ground, there is about 50 volts AC. When I hook up the third (ground) wire (never hooked up before), I finally have 120 volts between hot and ground, like I should have.

Any idea what is going on here? This is confusing.

[ben7]

Re: House wiring issue

Your meter could be picking up stray voltage?

[redwire]

Re: House wiring issue

What I've seen happen is old 2-prong outlets get replaced by 3-prong, but the wiring is left alone and the box is not actually grounded.
Your digital multimeter is sensitive, so it can give a reading on an ungrounded (floating) box. There is tiny capacitance and leakage current in the framing, all you need is 1-5uA to give you misleading readings.

I had to add ground wires on outlets, or sometimes there is actually a ground conductor inside, it's just been cut off so you can't see it. I thought it was around the mid 1950's when house wiring went 3-wire in North America?

[rhomanski]

Re: House wiring issue

I didn't move into new houses all that often, but what I saw was polarized plugs came first. Around the late seventies and then in the eighties the three prong came along.

I did in one case put a three prong outlet in an apartment once without hooking up a ground to the third prong. Only because it was an apartment. I wouldn't in my own house. I would go ahead and do it the right way. It's just apartment owners won't do it and would get upset if you tear up things to run new wires.

[redwire]

Re: House wiring issue

Apartment buildings follow different Building Code than houses - apt's must have wiring in metal conduit, which ends up grounding the boxes.

[budm]

Re: House wiring issue

I was helping my friend to find out if his outlet ground is connected to anything, I looked at the outlet box, they use 2-wire (Hot and Neutral), the metal outlet box has a copper wire attached to the box, the other end is attached to the Cold water pipe, so when you mount the outlet to the box, the ground on the outlet is grounded to the outlet mounting screws.
There is one outlet that shows open ground, so I looked the pipe where the ground wire was attached to, I saw one section of the pipe was fitted with PVC pipe, so the ground is broken. They do not allow to use Cold water pipe for grounding any more, they run the 3-wire to get the ground back to the panel. Not good to depend on the pipe for grounding, the house was built in the 60's.

[Hondaman]

Re: House wiring issue

The computer room is the one protected by the GFCI in the breaker box (I just moved in, but it is going to be my computer room). The third wire was just hanging there, inside the box on all four outlets. I hooked up the third (bare copper) wire up to the outlet or to the box. Now two of the outlets work correctly, and two do not work at all.

I rotated the four outlets to be "right side up". That's all I did, I swear. Why did power stop getting to two of the outlets? I have no explanation.

I thought the GFCI in the breaker box was a "whole house surge supressor". No, it is not. When I get the brick on the chimney examined and repaired, I'll definitely ask about lightning protection. I want this house to last (built 1964, it's a pretty solid house).

I'll call the professional electrician in the next week or two, and keep you posted. This is now beyond my skill level.

[Hondaman]

Re: House wiring issue

Oops, double post.

[japlytic]

Re: House wiring issue

I've read about some older buildings in the US may not be wired correctly, particularly with respect to the ground wire - also, I have read that someone had to run their seminar with the audience in their socks because the computers were sensitive to power disruption because the venue did not have proper grounding of the mains outlets.
So this is why some UPS units (especially US ones) have included a Site Wiring Fault indicator.