Question about voltage in U.S. house built in 1890

[niemand]

I tested the last grounded receptacle in my dwelling unit, which is the one in the kitchen being used by the refrigerator and the stove. The two outlets on this receptacle (non-GFCI) measured correctly: 122 V from ground to hot, and 0.005 V from ground to neutral.

[bdunham7]

I tested the last grounded receptacle in my dwelling unit, which is the one in the kitchen being used by the refrigerator and the stove. The two outlets on this receptacle (non-GFCI) measured correctly: 122 V from ground to hot, and 0.005 V from ground to neutral.

Did you test that 4-plex outlet with the stuff plugged into the other sockets?  If so, you probably just have a disconnect in the ground somewhere and leakage currents inside the various devices (like the UPS) are working like a voltage divider with the ground pins at the center.  A low-impedance (Low-Z) meter would give you a different result and there probably isn't enough leakage current to zap you too hard. 

[niemand]

...and the voltage that you're seeing from L1 to Ground is just from leakage.

What is "L1"? The hot contact on the outlet?

[niemand]

I tested the last grounded receptacle in my dwelling unit, which is the one in the kitchen being used by the refrigerator and the stove. The two outlets on this receptacle (non-GFCI) measured correctly: 122 V from ground to hot, and 0.005 V from ground to neutral.

Did you test that 4-plex outlet with the stuff plugged into the other sockets?  If so, you probably just have a disconnect in the ground somewhere and leakage currents inside the various devices (like the UPS) are working like a voltage divider with the ground pins at the center.  A low-impedance (Low-Z) meter would give you a different result and there probably isn't enough leakage current to zap you too hard.

Thanks. Not yet. It's got a very heavy desk right beside it, giving me only 4" of space. It's going to take some effort for me to gain adequate access. I don't know anything about a low-impedance meter. My DMM is just a cheap Kaiweets HT118A.

I'm trying to understand your idea that leaky currents inside devices can work like a voltage divider.... What are "ground pins at the center"? What do you mean?

[bdunham7]

I'm trying to understand your idea that leaky currents inside devices can work like a voltage divider.... What are "ground pins at the center"? What do you mean?

 

Here's a schematic of a typical IEC AC inlet filter.  Imagine you have 120VAC across L and N.  What would you expect to measure across L and PE or N and PE?  The capacitors form a voltage divider and if there is no other leakage and the PE is isolated (note that both PE terminals are connected to the case of the filter here) then the voltages across L/PE and N/PE would each be 1/2 of L/N. 

[CaptDon]

Conduit as a ground conductor or current carrying conductor is outlawed in the U.S. for good reason. Apparently in the O.P.'s house the wiring through the walls is mostly two conductor. As a matter of convenience many of the two prong outlets were replaced with grounded outlets but with no actual ground wire available. This is very typical of 'homeowner upgrades' when they have no clue about safety. I personally got thrown to the ground at a public swimming pool. I got out of the pool and went to play the jukebox standing on wet concrete. An inspection was made and it was a grounded outlet connected with no ground. The failure was internal to the jukebox putting the hot conductor directly to the metal frame of the jukebox. The owners of the pool said "We checked and didn't feel any shock although we had complaints". (They were obviously wearing shoes when they 'checked for shock').

[bdunham7]

Conduit as a ground conductor or current carrying conductor is outlawed in the U.S. for good reason.

Do you have a cite for that?  I don't think it is prohibited, at least not in the general case.  It certainly was acceptable and common in the past, no more than a few decades ago.  Receptacles used in metal boxes still have a feature where they 'self ground' to the box without any wires needed, although everyone bonds them with a wire and a clip nowadays.  It is totally plausible that whoever installed the current system in the OP's house didn't use any ground wires at all except for that one large one going to the meter box and that it passed an inspection that way.

[themadhippy]

Conduit as a ground conductor or current carrying conductor is outlawed

many would have you believe thats also the case in the uk.
Out of curiosity how is american conduit joined together,anything ive seem on line seems to be a clamp type arrangement,same for termination into a box? Over here metal conduit is threaded and screwed into a coupler to join lengths ,for boxes we use a brass bush and coupler

[bdunham7]

Out of curiosity how is american conduit joined together,anything ive seem on line seems to be a clamp type arrangement,same for termination into a box? Over here metal conduit is threaded and screwed into a coupler to join lengths ,for boxes we use a brass bush and coupler

There are two types of "conduit", EMT and rigid.  EMT is lighter and uses various devices such as single-screw retainers and compression clamps while rigid has pipe threads and couplers as the basic connection method.

https://www.eaton.com/content/dam/eaton/products/conduit-cable-and-wire-management/crouse-hinds/catalog-pages/crouse-hinds-connectors-couplings-emt-catalog-page.pdf

[niemand]

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.

For ground, I used my neighbor's grounding rod:


Probing the screw at the bottom of the panel...

...I got less than 0.5 V and a duty cycle of 300 Hz:



Probing the inside of the box...

...I got less than 0.1 V and a duty cycle of 60 Hz:


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.

[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]

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).

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]

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.

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.

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.

[BlownUpCapacitor]

So it looks like just a simple break in the ground connection somewhere in the building. I recommend hiring an electrician to do the job for you if you're uncomfortable doing it yourself. The fix is fairly simple. Just run a new ground line to that socket. Why not use the old one? Well, first of all it's gonna be a pain to get it out, fix it, then run it back. Plus if it's a broken conductor, it may not be in good condition to continue being used as a ground.

[Stray Electron]

...and the voltage that you're seeing from L1 to Ground is just from leakage.

What is "L1"? The hot contact on the outlet?

  The hot leg. 

     L1, l2, L3 actually apply to multi-phase power systems that have multiple hot legs 120 degrees out of phase with each other.  But I tend to think of U.S. residential power systems simply as a single phase systems or two phase power system with the phases 180 degrees out of phase with each other so I use the term L1 although it's actually N.A.

[Stray Electron]

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.

   Having no, or very low, voltage doesn't necessarily mean that the two points have a good connection. One of them may simply be floating i.e.  not connected.  You would have to put some sort of significant electronic load on the test point to be sure that it actually IS connected to ground.

   BTW your neighbors ground rod looks the way that ground rods should look.  They are required by code to extend above ground and the wire and clamp be clearly visible so that the connection can be verified by an inspector.  Years ago some people did just shove a wire in the ground and sometimes it would ground the system but usually the wire didn't go deep enough in the ground and the ground was very poor so people still got shocked.

[CaptDon]

I am living on a rural street in the states and our power situation seems to be very strange. I see one leg of what appears to be a 4160VAC circuit (2400VAC referenced to ground) and I see absolutely no return line what so ever? Only one single feed line crosses the main road to our road and amazingly it doesn't even have the protective lightning protector ground wire run above it!! There are 5 pole pig transformers on our road (25KVA each) with 3 to 5 houses on each one. I see only a 'home use' style ground rod at the bottom of each pole that has a transformer. I suppose the ground rods at each of our homes as well as the connection to our city iron water pipes (how's the electrolysis on those pipes I wonder) is forming the return? Is this typical of the U.S. power grid?? Seems like a poor way to do a power return and I wonder if it also leads to an early demise of the city water pipes?? Obviously, with only one feeder the whole neighborhood goes dark when a significant tree limb falls onto the feeder which seems to happen about three times each year. There is some sort of a fuse device out at the main road for our neigborhood which also seems to fail at least once each year.

[niemand]

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.

   Having no, or very low, voltage doesn't necessarily mean that the two points have a good connection. One of them may simply be floating i.e.  not connected.  You would have to put some sort of significant electronic load on the test point to be sure that it actually IS connected to ground.
[...]

Is this true even if the meter reads 5 V when I take the probe away from the plumbing pipe?

[Xena E]

I am living on a rural street in the states and our power situation seems to be very strange. I see one leg of what appears to be a 4160VAC circuit (2400VAC referenced to ground) and I see absolutely no return line what so ever? Only one single feed line crosses the main road to our road and amazingly it doesn't even have the protective lightning protector ground wire run above it!! There are 5 pole pig transformers on our road (25KVA each) with 3 to 5 houses on each one. I see only a 'home use' style ground rod at the bottom of each pole that has a transformer. I suppose the ground rods at each of our homes as well as the connection to our city iron water pipes (how's the electrolysis on those pipes I wonder) is forming the return? Is this typical of the U.S. power grid?? Seems like a poor way to do a power return and I wonder if it also leads to an early demise of the city water pipes?? Obviously, with only one feeder the whole neighborhood goes dark when a significant tree limb falls onto the feeder which seems to happen about three times each year. There is some sort of a fuse device out at the main road for our neigborhood which also seems to fail at least once each year.

Visiting some folks in a rural area of MS once it seems that this is, or at least was, a done thing to economise on feed line, I'm talking 10 miles of single feeder going to a settlement of sixteen properties... if this is the case in your location I'm guessing it is a small community?

The neutral return is the dirt!

[kjpye]

SWER (single-wire earth return) lines are widely used across Australia and other countries in less densely populated areas.

[soldar]

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.

A couple years after I bought this house I noticed the computer case giving me the tingles. After much investigating I found out the entire upper floor was not correctly connected to Earth.  Downstairs there is a register box near the ceiling which goes to a register box near the floor upstairs. This is a development with hundreds of identical houses so they prepared the bundles of cables, passed them through and connected them in each register box. Except that they had cut the earth cable just a bit too short so when they pulled the bundle through they pulled the far end into the conduit. Then they connected all the cables correctly except that the earth cable was not showing and was not connected. At first it was a mystery to me how a cable could go into a conduit at one end and not show up at the other end. It took me a while to think of the possibility they had cut the cable too short.

They work fast and often make mistakes.

[soldar]

It is good to know and understand the different types of earthing systems

https://en.wikipedia.org/wiki/Earthing_system

IEC terminology

International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.

The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):

    "T" — Direct connection of a point with earth (Latin: terra)
    "I" — No point is connected with earth (Latin: īnsulātum), except perhaps via a high impedance.

The second letter indicates the connection between earth or network and the electrical device being supplied:

    "T" — Earth connection is by a local direct connection to earth (Latin: terra), usually via a ground rod.
    "N" — the earth connection is supplied by the electricity supply network, either separately to the neutral conductor (TN-S), combined with the neutral conductor (TN-C), or both (TN-C-S). These are discussed below.

[themadhippy]

They work fast and often make mistakes.

biggest mistake was taking short cuts on the test and inspection of the finished job.