Odd voltages...

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daddyray

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I have a house with quite a bit of what I think is BX. All but one outlet have been upgraded to 3 prong, and all but the one read normal voltages (120v H-N, 120V H-G, 0V N-G).
In preparing to replace the last one (end of run), I noticed odd voltages:
120V H-N, 66V H-G, 41V N-G).
Noting a nearby heating duct (which I guessed to be grounded), I checked hot to the duct @ 120V, N-duct @ 0V, and G-Duct @ 41 V!

Going further, using an extension cord to an outlet I knew to be fed with 12-2 Romex, I read the following:
Continuity between (known)outlet ground and duct, with 0V (would seem to indicate the duct was a good ground);
Using the extension I got the following:

Known outlet BX Outlet
H-----------------245V-----------------------H (shows separate legs)
G-----------------121V-----------------------H
H-----------------145V-----------------------G
G----------------- 0V-----------------------N
G----------------- 40V-----------------------G
N------------------ 40V-----------------------G
H-----------------120V-----------------------G

All this says to my pea brain that I have about 40V on the BX outlet's ground (tho the H-G of 145V {known to BX} is odd). Any ideas?

I installed a GFCI (w/no ground), which seems to function normally.
So, should I worry about the "hot" ground? (Its a metal box, of course, so at least the cover screws will remain "hot"...)
Can I run a separate ground to the service (a new run is out of the question)? If so, can that be via the grounding cable to the grounding electrode, which happens to be outside the wall where the suspect outlet lives?

Thanks for bearing with me...
David
 
L

Lxnxjxhx

Guest
odd voltages

odd voltages

Put a low wattage bulb (7-1/2 watts or so) across the meter leads. Voltages due to capacitance between conductors which are incapable of supporting any load should go to zero.
 
480sparky

480sparky

Senior Member
Location
Iowegia
Either that, or you not seeing the little 'm' next to the big 'V'.

Big difference between the two. First you see this:

LCD1.jpg


Then you see this:

LCD2.jpg
 
D

daddyray

Member
odd voltages...

odd voltages...

I'm using a Fluke 87, and no, not looking at mv.
Would ghost voltage explain the 65V H-G? (It might explain N-G, but what about H-G. Should't H-G read 120V?)
Thanks again,
David
(Who thinks he knows what he doesn't know...)
 
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big john

Senior Member
Location
Portland, ME
If for some reason there isn't a solid ground in place, you'd get floating voltages like you described. Try putting a Wiggy in series, or a small lamp like someone suggested. See if the problem goes away.

If this is a really old house, maybe the armor on the BX is corroded to the point where it's a really poor bond, or the armor has come loose from a junction box somewhere?

See if the problem disappears when you measure at the next box upstream.

-John
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
Remove the line to the recep in question, remove it from the recep directly before it. Check the resistance between conductors. If you own a megger, give it a whirl, the recep in question is already removed, correct?
 
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daddyray

Member
odd voltages, cont...

odd voltages, cont...

Due to the construction of the house, and previous remodels, even finding a jbox or upstream recept. would be a challenge. If it is a loose ground, can I solve it by running a separate EGC back to the box (which I could easily do outside the wall, since the service is on the same wall on the other end of the house)? Maybe replace the metal box with plastic, to completely sever the loose ground?
Too hinky?
Not sure what a wiggy is...quick search came up insulation tester. Not sure how that would apply.
Thanks for bearing with me!
David
 
76nemo

76nemo

Senior Member
Location
Ogdensburg, NY
daddyray said:
Due to the construction of the house, and previous remodels, even finding a jbox or upstream recept. would be a challenge. If it is a loose ground, can I solve it by running a separate EGC back to the box (which I could easily do outside the wall, since the service is on the same wall on the other end of the house)? Maybe replace the metal box with plastic, to completely sever the loose ground?
Too hinky?
Not sure what a wiggy is...quick search came up insulation tester. Not sure how that would apply.
Thanks for bearing with me!
David
Click to expand...

I'm not confident with your problem, you'd have to isolate it for any of us to answer that. A seperate grounding conductor back to the panel:confused: Never heard of "hinky", and this forum probably wouldn't allow my alternative adjective:grin:
A plastic box won't solve anything. You can find the previous feed, think like the installer, that's vague, don't anyone give me grief. I am also not promoting working anything hot, so this could be a pain if not. Find your feed and go from there.

A "Wiggy" is a solenoid tester. Other posters are suggesting testing with low-Z inputs to rule out stray voltage.

Your turn,.......
 
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