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
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