House wiring problem

[mike]

Fine, don't believe Wikipedia. Search Google for thousands of incidences of people who have experiences with ghost or phantom voltage using digital meters.

Have a good weekend, David.

[Jack Hammer]

e:

A GFCI senses the difference between the current going to the load and the current leaving the load. If the current is not the same then it assumes the current is going through you. It then turns the current off.

[David Nebenzahl]

On 4/2/2010 11:12 AM mike spake thus:

It's getting *really* annoying hearing this same answer regurgitated every time someone reports a problem involving weird voltages in their home's wiring.

One would think that a DMM (digital multimeter) is a totally unreliable instrument, prone to erroneous measurements due to cosmic rays and pixie dust.

This is not the case. I just measured my unit's voltages with my DMM. Got 122-something volts between hot and ground, and 0.0 between neutral and ground, just like you're supposeta.

The OP has some screwy wiring, perhaps a floating ground, maybe something else.

(This isn't to say that it isn't *possible* for a DMM to misread due to stray capacitance or induced voltages, but it is nowhere near as terrible a problem as you hear here.)

[Stormin Mormon]

In this case, the OP got that voltage from each blade, to ground. So, it's not a ghost voltage. One of those oughta been hot, the other oughta been neutral.

[Stormin Mormon]

I'd suggest to buy a three bulb tester at the store, and see what that reads. Something sounds strange, with that set of readings.

[Stormin Mormon]

We lived, somehow, for years with non polarized two prong sockets. We had some problems, but everyone does.

[David Nebenzahl]

On 4/2/2010 2:45 PM mike spake thus:

Nope, I've got a Harbor Freight el cheapo (think I paid $3 for it). So how is it that I got completely accurate readings of my AC line voltage with it?

Sorry, I don't do Wikipedia (the "encyclopedia" that can be edited by any pimple-faced 7th grader).

[Nate Nagel]

It's not a problem, it's just the way that it works. It makes sense once it's explained.

The OP, I am 99% sure, *has* no ground, so that's why he isn't reading

0V between neutral and ground. His situation is more analogous to sticking one probe in the socket and just holding the other one in the air.

nate

[bud--]

I agree it was probably not the cause.

You can also add separate ground wires. Not necessarily a lot easier.

Time has marched on. AFCIs are now required essentially on all 15/20A

120V circuits that aren't required to have GFCIs.

Couple other options, but still a problem.

[clare]

Grounded Romex was introduced about 1947 . It hit the market in a big way in 1950 and was pretty standard by 1954 and the ground was required by code almost universally by 1962.

[clare]

your digital meter. It will "kill the Phantom"

[clare]

Depends a lot on the meter. With a Fluke or Amprobe meter, not very likely to have a problem, but with a $9.99 (on sale for $4.99) Harbour Fright special and many other cheap chinese DMMs it's almost a given.

[clare]

Just because YOUR cheap meter worked right when you tested YOUR circuit doesn't mean SOME other cheap meters won't misbehave or misread on SOME circuits - but I'd also lean towards it being a floating neutral (did I say floating ground in my first post??? - not sure - but floating NEUTRAL is what I meant to say.

[David Nebenzahl]

On 4/2/2010 4:00 PM Nate Nagel spake thus:

Agreed; the ground pin of his outlet is wired to nothing.

So why didn't that happen to me when I took my measurements? I put one probe in the socket, in the hot side, and the other in the air, and I got 0.0 volts.

Look--I understand the concept of phantom readings, and I know they're a problem under some circumstances. I just don't think they're as ever-present as some folks claim. I certainly have taken many accurate measurements using a DMM (and yes, comparing them to an analog VOM and gotten exactly the same results).

[gfretwell]

The air is not capacitively coupled to the other two current carrying leads the way it is in a receptacle where they are a fraction of an inch apart. Since a floating ground would be equally coupled to each of them the reading he gets makes perfect sense. The other place you see a reading like that is when you have an RF filter and no ground connection (like an ungrounded PC) The baseplate will be at exactly half the line voltage.

[David Nebenzahl]

On 4/2/2010 5:17 PM [e-mail] spake thus:

Didn't you read what I wrote?

I told you I used my cheap-ass HF meter and *didn't* get any phantom readings. So no, not a given.

So far, nobody has been able to offer a plausible explanation.

[Dave]

Hmm. Floating ground I think I understand. Floating neutral? Please tell me, what is this?

Thanks,

Dave

[Dave]

Planning on doing this tomorrow. Thought I had one, but can't find it.

Dave

[Dave]

A GFCI senses the difference between the current going to the load and the current leaving the load. If the current is not the same then it assumes the current is going through you. It then turns the current off.

Aah. Thank you. Much appreciated...

Dave

[Nonny]

Tony, please explain the fire without the abstract talk-around. Could you please explain it? Please explain a floating ground and how it can spark a fire.