120V, 49V, 51V on outlet test and hot ground

[WSP]

Hi folks,

Just ran into an alarming situation on our home wiring that has probably been a death trap in our house for years. I found the ground wires (in this case metal sheathing on old metal wrapped 2 wire cable) to read "hot" on an inductance meter. So the housing of our ceiling lights, the screws on outlet and switch plates, and everything else reads hot. I got a 'tingle' while holding a tool and touching one of the metal cables in the basement.

So I tested the outlets on this circuit and found that they read hot on the NEUTRAL side of the outlet, and the grounded metal, as described previously. And the LAST outlet at the end of the branch (I think ) reads hot on both neutral and hot sides (and the ground).

Multimeter readings at two of the outlets show ~120V across neutral-hot, around 49V from the actual neutral to ground, and 51V from actual hot to ground. If I reverse the probes on the actual hot-ground reading it drops to like 35V.

All appliances behave completely normally on all these outlets, but I remember now the ceiling fixture in the living room would often burn out CFL bulbs—seemingly long before they should have died.

Can anyone tell me what those crazy readings are all about? I've seen in another forum someone with a 70/50 V split in a situation that I didn't completely understand, but I seem to be losing 10V somewhere in the circuit as my readings don't add up to 120...

Any insight is greatly appreciated. Last ditch effort to make this safe or I fear the bill once an electrician comes in and tries to navigate all of the back story of this old house! I may just have someone out anyway to double-check me on all of this, but I'd least like to know what is going on.

 

[Reach4]

There should be an earth ground connected to the breaker box. This should connect to both the "ground" terminal bus and the neutral terminal bus. That needs some work.

I think there should also be a ground connection at the power company's equipment too. If the transformer services more than one house, each should have a ground grounding the neutral wire. I think for you to see what you are seeing, there is more than one failure.

I would contact the electric utility, and report what you see. They can fix their stuff, and have the other houses on that transformer fix their grounds. You may call an electrician to fix yours. But letting the power utility know first will be more likely to get other things fixed also. Plus they normally don't charge, so by the time you get your electrician in, things will have been diagnosed. I am not an electrician or other pro.

 

[Sponsor]

 

[WSP]

There should be an earth ground connected to the breaker box. This should connect to both the "ground" terminal bus and the neutral terminal bus. That needs some work.

I think there should also be a ground connection at the power company's equipment too. If the transformer services more than one house, each should have a ground grounding the neutral wire. I think for you to see what you are seeing, there is more than one failure.

I would contact the electric utility, and report what you see. They can fix their stuff, and have the other houses on that transformer fix their grounds. You may call an electrician to fix yours. But letting the power utility know first will be more likely to get other things fixed also. Plus they normally don't charge, so by the time you get your electrician in, things will have been diagnosed. I am not an electrician or other pro.

It is only the one circuit in the house that has this problem, actually. All modern/later circuits are fine.

 

[WSP]

So here's something new I just discovered. There is another circuit in the house that only has a few things on it, but it ALSO has hot ground. So I turned off the circuit breaker for THAT circuit and suddenly the first one is perfectly fine. The ground is not energized, and the readings are all normal again (even the hot is hot and neutral is neutral). So I think I'm dealing with some kind of cross-connection between these circuits. Anyone have any idea what the problem might be exactly?

If I turn off what I thought as the offending circuit, and leave on the newly discovered problem circuit, the ground of one fixture on the original suspect circuit is still energized, AND the ground of the new suspect is hot, too. But all outlets on the old suspect are totally dead. And the readings on the new suspect in this case are 120/120/0 as normal.

So one further thought, is that there are two light fixtures on these suspect circuits that are wired to two switches. One functions in a typical 3-way configuration, but it's wired the old way where even when the light is off, the hot wire is still energized. The other one is wired strangely. There is a dependence on one switch being on, for the other switch to work as off/on, but the limiting switch can always turn it off/on.

I'm wondering if maybe bad wiring for the light switch behaviors is causing all of this??

 

[Reach4]

I would measure the voltage from the neutral line in the box to an earth ground. I know how to probe around in there safely. A metal water pipe would often be a good earth ground. As a meter reference, the ground does not have to be a really good low impedance ground.

If you are not confident that you can safely pull the cover of the breaker box to access the lines there, what voltage do you read from the ground (third terminal) of outlets to an earth ground?

The neutrals (white wires) and ground (green or bare or yellow+green) are connected together inside of the main breaker box.

 

[Jadnashua]

Older wiring can get brittle when it ages. It might be fine until you move it, and then insulation cracks off. That can create all sorts of safety problems. Are the receptacles 3-prong? Is there an actual ground wire in the cable, or does the system use the BX sheathing as ground, and maybe a short wire screwed to the metal box to get ground to the receptacle? Older BX cannot be relied on for a good ground...the newer stuff has a ground lead in it.

A high impedance multimeter can 'see' voltages that have no current capacity, and can be misleading. But, if you feel a tingle when touching anything that is supposed to be grounded...you have a real safety issue. Under the right set of conditions, it could kill you.

I'd approach this problem by starting at the source (breaker box), and tracing things to the first electrical box. Disconnect things there, and see if you get normal readings. If you do, reconnect things, and move to the next box in the chain...remove the outlet (feed-through) and test again. If it's still good, the problem is further down the line. Keep doing that until you find a point where you have a problem when the feed-through is disconnected...then, the problem is between the last point where it was good and the box you are working on.

There are some fairly inexpensive circuit tracers that put a signal on the line, and then you can 'listen' for it with a receiver to help you trace the wiring.

 

[WSP]

Reach4, the neutral bar in the box is directly connected to a gigantic, new ground cable running right across the water meter and into ground, so no worries there.

Jim, this is indeed pretty old BX on both of the suspect circuits.

So the latest here is a bit puzzling, but it brings into scope something I'd not previously considered, since we're talking about the BX as ground possibly not working well. I had just removed some obsoleted wiring from a box in the attic that is on one of the suspect circuits, and I believe in doing so I must have removed the good grounding on that circuit somehow. On a hunch, I directly grounded that box in the attic to a good ground, and the "hot" inductance meter reading on the ground of both circuits went away. Immediately, the strange 120/49/51 readings stayed the same, but after leaving that ground attached overnight, today the reading on all outlets is also normal (though reversed on a few) at 121/120/1. So I am now wondering if having that ground disconnected/weak slowly builds up some kind of charge on the ground of both circuits and throws the meter readings out of whack. And then after the ground is properly working, slowly over time the charge dissipates and readings are "right" again. Ever seen this kind of lag effect in readings?

 

[Reach4]

I suggest you wire one probe of your meter to a good ground, and measure the voltage at the ground lines and neutrals at the outlets.

Your lag effect thing is not a thing.

 

[WSP]

Your lag effect thing is not a thing.

It may not be a thing, but that is consistently how it is behaving. It takes like 20-30secs after reconnecting/disconnecting that ground for the 'hot' reading off the inductance meter to return to the ground wiring of the suspect circuits. It clearly reads not energized for that 20-30 second gap.

The voltage from the outlet's neutral to a copper radiator pipe next to it is 0.1V. From neutral to the outlet's own ground wire is 1.0V.

 

[Reach4]

Try the measurement again when you get a 120/49/51 reading.

 

[WSP]

Try the measurement again when you get a 120/49/51 reading.

Will try if I get the 120/49/51 again. Further info: There is a .8-9V reading from outlet ground to copper pipe—that's there regardless of "hot" ground or not. Also, the voltage read from the "hot" light fixture casing to a good ground is about 1.6-1.7V. And that voltage drops to 0, when I put the ground 'bridge' back in place and the light fixture no longer reads "hot". And further info, I have decided I am simply wrong about the 20 sec gap business. It very much seemed to be a thing. But now it doesn't.

So I am starting to think the inductance meter is picking up this 1.7V and saying "hot!", because of that. And that the voltage drop is due to the difference in resistance between the metal sheathing of the old circuit's ground, and the solid copper of a proper new ground. I am feeling those weird readings I was getting may have been a fluke?

Questions that come to mind, though, are: why is this 1.7V potential in the circuit in the first place? Neutral touching the metal cladding somewhere due to deteriorated insulation, and passing that little V that reads in neutral-ground into the ground? I know there is also a little current passed with that 1.7V because I felt a little shock—that's how I discovered this problem... It feels like the same shock that is common in live music venues when instrument on stage is plugged into and outlet that's different from the PA, and you get a pretty good shock at the mic. I feel like in those situations the path to safety was just to run the stage and PA both to rock-solid grounds.

 

[Reach4]

Questions that come to mind, though, are: why is this 1.7V potential in the circuit in the first place?

If the neutral was carrying 10 amps back to the grounded bus terminal, and if the resistance of the wiring was 0.17 ohms, that would give 1.7 volts. If the resistance of the wiring was 1.7 ohms and the wire carried 1 amp, that would also give 1.7 volts.

I know there is also a little current passed with that 1.7V because I felt a little shock—that's how I discovered this problem... It feels like the same shock that is common in live music venues when instrument on stage is plugged into and outlet that's different from the PA, and you get a pretty good shock at the mic. I feel like in those situations the path to safety was just to run the stage and PA both to rock-solid grounds.

That's unexpected -- that you would feel the 1.7 volts. The threshhold of perception at 60 hz is about 1 ma. To get 1 ma from 1.7 volts would call for body resistance of 17 kilohm. That presumes elsewhere on the body is somewhat grounded. However just because you detected 1.7 volts now, it is not higher another time.

One test of the voltmeter is to ground one probe and to grab the other with your finger. A typical high impedance voltmeter can show surprisingly high voltages that way.

 

[WSP]

If the neutral was carrying 10 amps back to the grounded bus terminal, and if the resistance of the wiring was 0.17 ohms, that would give 1.7 volts. If the resistance of the wiring was 1.7 ohms and the wire carried 1 amp, that would also give 1.7 volts.


That's unexpected -- that you would feel the 1.7 volts. The threshhold of perception at 60 hz is about 1 ma. To get 1 ma from 1.7 volts would call for body resistance of 17 kilohm. That presumes elsewhere on the body is somewhat grounded. However just because you detected 1.7 volts now, it is not higher another time.

One test of the voltmeter is to ground one probe and to grab the other with your finger. A typical high impedance voltmeter can show surprisingly high voltages that way.

I was sweaty at the time, so if my resistance was down to 1000, I'd have been at 1.7mA. People usually get zapped at live shows on their lips, which I guess also decreases resistance. Anyhoo, still wondering how I'm getting any kind of current on the ground at all. Would you expect it was due to some amount of current passing through old insulation? Where the danger could be coming from is what I'm trying to pinpoint I guess at this point.

 

[Bgard]

with the way the three way switches are wired (I have seen that in old houses before) the hot and neutral are reversed at times, which means that the screw shell of light fixtures can be on the hot side at times, I have seen where the screw shell was touching the metal housing that the socket is mounted in. the socket that I am talking about are two pieces, the socket is mounted on a porcelain base and has a porcelain nut, the socket protrudes through the metal fixture and the nut secures it. I have seen the nut come loose and then the shell of the socket can touch the metal fixture if there is not a good ground path the metal parts of the circuit will become energized

 

[Tony Hwang]

Hi folks,

Just ran into an alarming situation on our home wiring that has probably been a death trap in our house for years. I found the ground wires (in this case metal sheathing on old metal wrapped 2 wire cable) to read "hot" on an inductance meter. So the housing of our ceiling lights, the screws on outlet and switch plates, and everything else reads hot. I got a 'tingle' while holding a tool and touching one of the metal cables in the basement.

So I tested the outlets on this circuit and found that they read hot on the NEUTRAL side of the outlet, and the grounded metal, as described previously. And the LAST outlet at the end of the branch (I think ) reads hot on both neutral and hot sides (and the ground).

Multimeter readings at two of the outlets show ~120V across neutral-hot, around 49V from the actual neutral to ground, and 51V from actual hot to ground. If I reverse the probes on the actual hot-ground reading it drops to like 35V.

All appliances behave completely normally on all these outlets, but I remember now the ceiling fixture in the living room would often burn out CFL bulbs—seemingly long before they should have died.

Can anyone tell me what those crazy readings are all about? I've seen in another forum someone with a 70/50 V split in a situation that I didn't completely understand, but I seem to be losing 10V somewhere in the circuit as my readings don't add up to 120...

Any insight is greatly appreciated. Last ditch effort to make this safe or I fear the bill once an electrician comes in and tries to navigate all of the back story of this old house! I may just have someone out anyway to double-check me on all of this, but I'd least like to know what is going on.

Your house might have a floating ground or poor grounding. Really between neutral and ground it should read zero volt. Also use old analog meter
instead of digital multi meter. Digital meter has high Z input terminals which will pick up voltages even from your finger tips. One reason I still
keep old Simpson 260. Any way how old is the house? Has Cu wiring? Do you have some GFCI in the house? Time to investigate starting from main line coming into your house panel. Again please use an analog meter.

 

[WSP]

There are indeed 3-way switches on both circuits in question. One is wired the 'old code' way where they allowed for one combination of switch positions to have an energized black even though the light isn't on. The other one is pretty wacky. One switch must alway be up/on for the other switch to have any effect. I have no idea how that one is actually wired. I guess it's just single wire loop with two single-pole switches in there. Would there be any other way that could be wired to work with a dependency on the 'first' switch being on?

I feel there must be a ground issue somewhere, but it is only on these two, older circuits. The house is 92 years old, and the metal-clad wiring is probably that old, as it was buried in the horsehair plaster in the basement ceiling. I am pretty concerned about the condition of the insulation on the wires inside the metal wrap.

I am wondering if I could simply ground the part that's funky to the point where no voltage is read on the surfaces of fixtures, and then just put AFCI-GFCI breakers on those two circuits and come away safe. What do you think? Arc protection and GF protection would pretty much cover everything, right? I could flip the polarity of the two outlets I found that read reversed, too...

Right now I just want to come away safe. I'd really like to just go ahead and replace all of this old wire with Romex, but not sure I can afford it and don't really know if I want to get into the walls right now...

 

[WorthFlorida]

FYI... If you all recall the old analog telephones worked at -48v DC . The reason was the human body will start to feel the voltage around 50 volts, hence the little tinkle because it is AC current.

You might be relying too much on what the meter is reading. My way of troubleshooting has always been eliminate and isolate.

Go back to where when you turned off the breaker and the voltage read what looked like to be normal on the other circuit.. On these two circuits, disconnect all appliances, and light bulbs. Turn power on and check your voltage. If it reads wrong, then start opening up all outlets and light fixtures. I would remove (disconnect) all outlets and switches, turn on the power and check voltages again. Then start replacing all outlets first with new ones. check voltages after each one is replaced. Then replace all wall switches with new ones and again check voltages after each switch is replaced. The screw in light bulbs and plug in appliances. One step at a time. If the problem shows itself again then you can leave that part of the circuit disconnected and may have to live with a few dead outlets or light until you can get is all corrected.

When the problem clears and if it comes back you narrowed down the section of wire, switch, outlet or appliance that may have some leakage. This is very simple procedure that I have used for over forty years. You could have a screw form a wall switch or outlet that has cut into the insulation of the wire. The box may not be grounded or has high corrosion thus there is no hard short to trip a breaker. I used to work on paging systems and one time I must have open a dozen wall volume control covers. Sure enough one of them had a 3" long 6-32 machine screw and it wrapped around the speaker wire.

 

[Bgard]

most of the time the wire inside the steel sheath is in surprisingly good condition, it's just where the wires are exposed to air and heat in outlet boxes that the insulation becomes very brittle. if one of the three-way switches is not wired correctly it will always be required to be in the same position for the other one to work, someone my have tried to replace the switch and didn't know how it was wired before they changed it. rewiring is the best option. you can bond the BX cable to the rest of the electrical system, but you also need to be sure that the main service is properly grounded to an earth ground source and the neutral needs to be grounded at the main service entrance panel. arc fault and ground fault breakers and a level of safety but until you get the grounding and reversed polarity situation corrected the gfi's and the arc's may trip as soon as you turn them on.

 

[Jadnashua]

The shell of BX and the screws used to anchor it do not make the best ground once they start to age. A little moisture (humidity is enough) over time, and you can get a high resistance connection. Throw in temperature changes and thermal expansion/contraction, and the connection's resistance can vary.

Having one 3-way switch not function properly is almost always caused by miswiring it. When replacing a switch, you need to carefully watch which screws are travelers, and which is the hot. They aren't always in the same orientation on different switches. IOW, you need to understand their function to get them back on the right terminals.

 

[WSP]

You might be relying too much on what the meter is reading. My way of troubleshooting has always been eliminate and isolate.

You may be right. I don't really want to open and disconnect every outlet, switch, light, but maybe I'm just going to have to. My fear was that pulling on wires in order to get every switch/outlet pulled might cause another problem by breaking up the brittle ends of this old stuff. But may be no choice. If what bgard says is true, maybe if I'm careful I can make it happen with no worse outcome.