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weird voltage sniffer results


AHI in AR
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I inspected an 80 year old home this afternoon and encountered an odd result with my voltage sniffer. The home had an enclosed rear porch with a 50 year old or so water heater (Clayton Lambert Alumilux, but that's another story), a fuse box, and a clothes washer and dryer.

As I turned on the tester and swung it over to check for voltage at the fusebox housing before opening it, it alerted when I got it within about a foot from the water heater vent. I then checked it near the other metal items in the room. It did the same near the washer, but not the dryer. If I touched either item, it quit alerting. For the record, the washer had braided stainless steel hoses.

The home had a crawlspace door that was locked, so I couldn't get under there. But inside the home, I could see that a lot of the water distribution lines were now cpvc. Those in the laundry room porch were copper. The grounding method appeared likely to be only the water lines as there was no ground rod visible. I could not tell what the water service material was where it entered the crawlspace since I couldn't get under there, so I don't know if the water lines were truly grounded. I have seen more than one home this age with a newer plastic water supply line and the ground wire still clamped to an orphaned copper pipe downstream.

The grounds and neutrals were mixed at various places downstream of the service panel, and there was a lot of amateur wiring. There was also some active knob and tube, although it was hard to see much with 14" of insulation in the attic.

My guess is that there was some voltage on the water lines from the mixed grounds and neutrals. But I didn't get a tingle when I touched the water heater or the washer, nor did I read any voltage when I tested from the hot on the fusebox to the water heater housing or the washer housing.

Any of you electrical geniuses know what's going on?

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Originally posted by Richard Saunders

One reason you need to carry a multi meter. A sniffer will detect any magnetic field and will often "alert" on any ungrounded appliance like a water heater or dryer. I would suspect lack of grounding rather than a short or stray current.

Why would a gas water heater give off a magnetic field? And the washer was the issue, not the dryer.

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I think we can guarantee that the copper piping in the porch has no connectivity to a grounding electrode; even if there was one(?).

If the washing machine was running when you got these results...

Washing machine is not grounded (2-prong receptacle, etc, etc) and you are reading the magnetic field at the washer which is also travelling along the braided SS hoses and the copper lines to the water heater.

If it wasn't running then I would suspect the same as above with the added extra that the washer receptacle has reversed polarity.

In either case, I doubt there is any actual voltage as you were able to "drain" the field by simply touching either appliance. Kind of the same thing you can do with an ungrounded toaster or ceiling fan(try it).

With the fuse box, KT, and amatuer wiring, it sounds like the home is overdue for a new, properly grounded service and new circuit wiring. I'd report it as (further) evidence of the lack of modern grounding and bonding and suggest they get some quotes for complete electrical upgrade. Or summit like dat!

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The washer was not running at the time I was there. I did not check the receptacle since it was floor mounted behind the washer, and I didn't want to scar up the recently painted wood floor moving the washer out 3' to get to the receptacle.

I did tell' em to essentially rewire the whole place if possible since fixing all the above issues and the others I found would be about equivalent to a total re-do anyway. I expected the usual 80 years of wear, poorly done add-ons, rodent gnawed wires and the like. I was just curious about why I could get the sniffer to light up a foot or more from the appliances. Thanks for the replies.

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Originally posted by AHI in AR

. . . My guess is that there was some voltage on the water lines from the mixed grounds and neutrals. But I didn't get a tingle when I touched the water heater or the washer, nor did I read any voltage when I tested from the hot on the fusebox to the water heater housing or the washer housing.

Any of you electrical geniuses know what's going on?

From your description, I agree with Richard & Richard. The appliances weren't grounded and you were simply picking up the electric field that naturally surrounds any energized wire, fixture or appliance. The Richards pretty much explained it but the field that you detected and that they're talking about is the electric field, not the magnetic field.

Here's how it works. Your volt sniffer isn't really a voltage detector. It's more like an electric field detector. Every energized wire, fixture and appliance has an electric field around it. Through the magic of capacitive coupling, you can detect these fields with a volt sniffer.

Unfortunately, electric fields don't only exist around things that are energized with line voltage. They can also exisit around things that are near things that are energized with line voltage. So, sometimes, your detector will seem to be telling you that something is "hot" when it's not.

To make it more complicated, you can dampen or drain the electric field by surrounding the energized thing with a grounded metal shield (a Faraday cage). Once this is done, your volt sniffer can no longer detect the field. So, sometimes, your detector will seem to be telling you that something is not hot when, in fact, it is.

Because of this tendency to give both false positives and false negatives, I place little trust in volt sniffers.

- Jim Katen, Oregon

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Originally posted by Jim Katen

...

The appliances weren't grounded and you were simply picking up the electric field that naturally surrounds any energized wire, fixture or appliance. The Richards pretty much explained it but the field that you detected and that they're talking about is the electric field, not the magnetic field.

...

Thanks Jim. I think in future I'll use the term electromagnetic field (EMF) as that includes both types. My knowledge of how to use electricty safely isn't too bad but I'll be the first to admit I'm weak when it comes to the theory behind the "magical" invisible force.

This is an interesting read...

http://www.who.int/peh-emf/about/WhatisEMF/en/

It helps, but there is much of it that makes my head hurt!

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Originally posted by Richard Moore

Originally posted by Jim Katen

...

The appliances weren't grounded and you were simply picking up the electric field that naturally surrounds any energized wire, fixture or appliance. The Richards pretty much explained it but the field that you detected and that they're talking about is the electric field, not the magnetic field.

...

Thanks Jim. I think in future I'll use the term electromagnetic field (EMF) as that includes both types.

Just remember that there is no EMF if the device isn't running. Only the electric field portion is present. When the device is running, then you've got both electric and magnetic fields present.

This is an interesting read...

http://www.who.int/peh-emf/about/WhatisEMF/en/

It helps, but there is much of it that makes my head hurt!

That's a very clear explanation but I believe that it contains an error in the first paragraph. It says that if current does flow . . . the electric field strength will be constant. In my experience, when current flows, the electric field shrinks, making it harder to detect.

This is interesting stuff, but it can get very confusing.

- Jim Katen, Oregon

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