Electronics > Repair
Question about voltage in U.S. house built in 1890
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ArdWar:
PE getting to half line voltage is almost certainly a ground wiring fault (or that particular socket is not grounded at all), and some appliances connected to the same socket (or same network with faulted ground) are backfeeding the PE.

I'm almost certain with that since the other likely explanation, your utility failed to ground their transformer properly, is fairly unlikely (it *do* happen however, and deliberately done in IT system which isn't usually used for residential).
SeanB:

--- Quote from: ArdWar on May 16, 2024, 03:52:40 am ---PE getting to half line voltage is almost certainly a ground wiring fault (or that particular socket is not grounded at all), and some appliances connected to the same socket (or same network with faulted ground) are backfeeding the PE.

I'm almost certain with that since the other likely explanation, your utility failed to ground their transformer properly, is fairly unlikely (it *do* happen however, and deliberately done in IT system which isn't usually used for residential).

--- End quote ---

Hard to do in the USA, as the pole pigs ( house supply transformers) almost always have the neutral connection not isolated from the case, and a ground wire for both the incoming and outgoing supplies, along with ground bonds at each service point. Thus even if the transformer has lost ground, it will be completed via all the other houses, which can make for some hot ground cables on them, and a large neutral earth drop.

Here the house got upgraded to 3 wire outlets but was not rewired, and the only solution is to keep the meter, and replace all the rest with new. If it is rented the landlord is responsible to provide a safe electrical supply, and if it is owned by OP then the seller was responsible to have the house upgraded to comply to the minimum modern scec before transfer.
CaptDon:
It looks like my statement of EMT being disallowed as a ground conductor by NEC rules is wrong. It seems EMT is allowed with certain parameters like "Tight fittings" or "Steel Couplers" etc. My information (which I sadly accepted as being an NEC rule) came from and is because of the fact that local municipalities and fire ordinances are allowed to be applied over and above the NEC codes. Generally speaking, no one in their right mind would allow installing a 20 amp receptacle in a steel box 30 feet away from a main panel including 3 10ft pieces of EMT and 4 couplings and being fed with 12/2 and using the conduit and couplings as the sole source of grounding as being reliably safe over the long term that a house may last! Local codes (which I state as sensible) mandate a ground conductor of 'Not less than one AWG size smaller than the current carrying conductors' or as we all do, just wire the receptacle with 12/2 CU with 12 CU ground NM-B run inside the conduit. NEC section 250.118 and related also 310.
CatalinaWOW:
My only comment is that while previous posts have stated that poor ground bonding is uncommon or rare, I have found it in more than a quarter of the places I have lived, only one of which was built prior to 1950.

The only way to know is through measurement, and don't be too surprised at what you find.
tooki:

--- Quote from: niemand on May 16, 2024, 02:24:00 am ---
--- Quote from: BlownUpCapacitor on May 14, 2024, 06:20:02 pm ---Use a DMM to measure the potential of those boxes to ground. Should be near zero or under 10v. I wouldn't go touching those boxes if they are at an elevated voltage.

--- End quote ---
For ground, I used my neighbor's grounding rod:
(Attachment Link)

Probing the screw at the bottom of the panel...
(Attachment Link)
...I got less than 0.5 V and a duty cycle of 300 Hz:
(Attachment Link)


Probing the inside of the box...
(Attachment Link)
...I got less than 0.1 V and a duty cycle of 60 Hz:
(Attachment Link)

Compare with probing the plumbing pipe in the bathroom using the ground from the GFCI outlet (like I did yesterday in my reply #17):
I got 0.005 V and a duty cycle of 60 Hz.

--- End quote ---
FYI, Hz is the frequency. Duty cycle is a completely different thing (expressed in %) that applies mostly to square waves.

300Hz is noise of some type. The line frequency in USA is 60Hz and won’t vary to any meaningful degree, so it’s not something that has any diagnostic value in household mains wiring.
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