Low leg / High Leg

[dcg9381]

So eventually, I'm going to have to figure this out:

I got called to "help" a neighbor during the last "It's about to freeze". They have a well house. The complain was that the GFCI "outlet" wasn't working and they couldn't run a heater on the pump house... They were on "electrician" #3 and up against the freeze.

I went out there, sitting along side were 2-3 "old GFCI" outlets that had been replaced. I tested the existing one, it was fine. No problems. Traced everything internally on the pump house. Everything connected right, wired right, proper breaker size. No faults.

Only "code" fault I can see is that the "out building" does not have it's own ground. But it's on a 4-wire feed. No GFCI fault.

So I probed L1/N and L2/N.
L1/N was 109V.
L2/N was 141V.
L1/L2 ~240V.


Ballistically I determined that their little electric heater did not like 141V. It would not turn on.
I have not probed the main on the house... But they worked around by running an extension from the house, so I assume that's OK.. I could also "swap" the legs and run this on the 109V leg.

Any guesses on it if it's not the main?

 

[rlitman]

Are you getting those voltages with any load on, or no load? Either way that's indicative of a "loose neutral". Knowing where the load is may help you to isolate where the problem is.

 

[dcg9381]

Are you getting those voltages with any load on, or no load? Either way that's indicative of a "loose neutral". Knowing where the load is may help you to isolate where the problem is.

No load. I walked traced it up to the sub-panel in the "building". Well pump wasn't running nor was the accessory pump. There WAS a pump controller that was on, but that's it.... So it doesn't feel like one side was being pulled down to me.

 

[LXCam]

Did you check line to ground? Also check neutral to ground.

I’m with rlitman that it looks like a neutral issue.

 

[Wrench97]

I'd check the house side of the "pump controller" first to verify if it does or does not have the same voltages on each leg.

 

[mm08822]

May be worth while starting at the beginning of the feeder. Your call based on condition/impression of the entire premises.

Turn off the cbs in the pump house.
Inspect/check sub-panel terminations
Read voltages:
L1/N
L2/N
L1/L2
N-Grd

Add a load on L1 only (heater, light, etc.)
Read 4 voltages

Add a load on L2 only (heater, light, etc.)
Read 4 voltages

With both loads on, read 4 voltages.

 

[dcg9381]

Did you check line to ground? Also check neutral to ground.

No. Expand on what results mean on different measurements.

I'd check the house side of the "pump controller" first to verify if it does or does not have the same voltages on each leg.

I can shut all the draws off easily. The pump controller is 240V out, if I recall right and shutting EVERYTHING down off the sub, I still had these odd high/low readings. The pump controller is L1/L2/ground.

May be worth while starting at the beginning of the feeder. Your call based on condition/impression of the entire premises.

1970 premises if that tells you anything. But a feed from the main directly doesn't upset the heater. I was "remiss" not to go upstream, but I'm doing this for free and was busy trying to get my place ready for a freeze.

I mean it was wired in the 1970s, so it *****. I'm OK with "it *****", but I'm not getting on the dock that has a non-GFI feed.

I'll definitely check the main and the breaker output to the "pump house".

I only get these calls when they want it done "right now" or it's critical.....

 

[wyliesdiesels]

So eventually, I'm going to have to figure this out:

I got called to "help" a neighbor during the last "It's about to freeze". They have a well house. The complain was that the GFCI "outlet" wasn't working and they couldn't run a heater on the pump house... They were on "electrician" #3 and up against the freeze.

I went out there, sitting along side were 2-3 "old GFCI" outlets that had been replaced. I tested the existing one, it was fine. No problems. Traced everything internally on the pump house. Everything connected right, wired right, proper breaker size. No faults.

Only "code" fault I can see is that the "out building" does not have it's own ground. But it's on a 4-wire feed. No GFCI fault.

by "ground" do you mean grounding electrodes? if not, then what else do you mean by this since you state it has a 4-wire feed which should be hot hot neutral EGC (ground).

So I probed L1/N and L2/N.
L1/N was 109V.
L2/N was 141V.
L1/L2 ~240V.


Ballistically I determined that their little electric heater did not like 141V. It would not turn on.
I have not probed the main on the house... But they worked around by running an extension from the house, so I assume that's OK.. I could also "swap" the legs and run this on the 109V leg.

Any guesses on it if it's not the main?

I agree with others on bad neutral BUT.... L1 to N and L2 to N should add up to the same voltage as L1 to L2.... something is amiss here

 

[wyliesdiesels]

No. Expand on what results mean on different measurements.

Neutral is bonded at first means of disconnect/main service panel. so metering from neutral to ground (EGC) should show 0v and continuity. If you get voltage it means you have a compromised neutral and or ground (EGC)....

 

[Bert_]

You 100% have a neutral problem. The next logical step is to check voltage wherever the pump house is power from. Could be a bad connection, could be a wire in the ground. Need to finish troubleshooting

 

[BurtEggley]

I would go back to the main panel and see what you have there. The neutral issue could even be a POCO problem. Sounds very much like the neutral and ground have about 15V - 16V potential.

That said, we've had situations here where a leg on the transformer down the street went out. The POCO came in and put some kind of temporary transformer on it for a couple days to feed the homes. One one or two occasions over the last 35 years, the two legs in were not always balanced but never that far apart. We saw some channel the other day on Youtube where a guy was called to a house to do electrical work. He got there and went to the panel. On the side of the house the POCO had set up some kind of a transformer with wheels they rolled up, maybe about like a suitcase to carry on a plane. They had it wired from and then back into the panel. Guy who was called out just said call me when the POCO is done. He didn't want to trouble shoot the problem until they had normal power. I seem to recall he did a quick test with a VOM and got goofy readings like in this thread.

 

[wyliesdiesels]

I would go back to the main panel and see what you have there. The neutral issue could even be a POCO problem. Sounds very much like the neutral and ground have about 15V - 16V potential.

That said, we've had situations here where a leg on the transformer down the street went out. The POCO came in and put some kind of temporary transformer on it for a couple days to feed the homes. One one or two occasions over the last 35 years, the two legs in were not always balanced but never that far apart. We saw some channel the other day on Youtube where a guy was called to a house to do electrical work. He got there and went to the panel. On the side of the house the POCO had set up some kind of a transformer with wheels they rolled up, maybe about like a suitcase to carry on a plane. They had it wired from and then back into the panel. Guy who was called out just said call me when the POCO is done. He didn't want to trouble shoot the problem until they had normal power. I seem to recall he did a quick test with a VOM and got goofy readings like in this thread.

its a 1:1 transformer that takes whatever feed is working from the pole (either 2 hots or 1 hot and neutral) and generates a 3-wire MWBC split phase circuit so the electrical system in the home can function properly.

 

[LopezBart]

Note that if you have a very unbalanced 120V load on a long run of 240/120, the voltage drop will be the same value on the neutral leg as on the hot leg - e.g. the hot leg will drop, and the neutral will go up wrt ground.

 

[rlitman]

...I agree with others on bad neutral BUT.... L1 to N and L2 to N should add up to the same voltage as L1 to L2.... something is amiss here

I agree that 109 + 141 does not add up to 240, but unless there were two meters measuring both at the same time, I'd say this is close enough. The loose neutral problem here exists somewhere between the circuit that was measured and the transformer (at the pole?). With a loose connection, the resistance will vary quite a bit (arcing heats it up raising the resistance, but the arcs themselves lower it), and any change in the load (someone turning on or off lights anywhere downstream of the problem) will change the voltage across the loose connection as the current changes. So I'd expect the numbers to jump around a bit.

Anyway, a loose neutral is a dangerous condition that should be found and corrected ASAP!

 

[dcg9381]

I agree that 109 + 141 does not add up to 240, but unless there were two meters measuring both at the same time, I'd say this is close enough.

Yea, there is some variation out here in voltage to the mains. I don't remember what the tolerences were, but at my place it runs a little hot, maybe 248V or so. I had an issue last year where my inverter was detecting over-voltage at the main and it took a while to get the POC to accept that it really was a problem. I had to log WHEN it happened.

Anyway, a loose neutral is a dangerous condition that should be found and corrected ASAP!

Got it.. I'll get my *** back out there and do a little more testing.

 

[rlitman]

...Got it.. I'll get my *** back out there and do a little more testing.

Good. Start at the main panel and check the L-N neutral voltages there. If the problem is seen on the main lugs, then it could be in the meter pan (still the customer's problem) or the service connection or transformer (the power company's problem).

I would go back to the main panel and see what you have there. The neutral issue could even be a POCO problem. Sounds very much like the neutral and ground have about 15V - 16V potential.

That said, we've had situations here where a leg on the transformer down the street went out. The POCO came in and put some kind of temporary transformer on it for a couple days to feed the homes. One one or two occasions over the last 35 years, the two legs in were not always balanced but never that far apart. We saw some channel the other day on Youtube where a guy was called to a house to do electrical work. He got there and went to the panel. On the side of the house the POCO had set up some kind of a transformer with wheels they rolled up, maybe about like a suitcase to carry on a plane. They had it wired from and then back into the panel. Guy who was called out just said call me when the POCO is done. He didn't want to trouble shoot the problem until they had normal power. I seem to recall he did a quick test with a VOM and got goofy readings like in this thread.

I know someone who had a bad connection on one leg of an underground service. The generator ATS wouldn't switch back to utility, and after diagnosing, I suggested calling the utility. The power company dropped off one of these to get her going until the ground could defrost and they could make the permanent fix. https://bridgeportmagnetics.com/temporary-power-restoration/
It's an autotransformer that can make up for a missing leg or even missing neutral. A real neat solution to an otherwise difficult problem.

 

[Shiftless]

Anyway, a loose neutral is a dangerous condition that should be found and corrected ASAP!

Agreed

 

[Codyboy]

Good. Start at the main panel and check the L-N neutral voltages there. If the problem is seen on the main lugs, then it could be in the meter pan (still the customer's problem) or the service connection or transformer (the power company's problem).


I know someone who had a bad connection on one leg of an underground service. The generator ATS wouldn't switch back to utility, and after diagnosing, I suggested calling the utility. The power company dropped off one of these to get her going until the ground could defrost and they could make the permanent fix. https://bridgeportmagnetics.com/temporary-power-restoration/
It's an autotransformer that can make up for a missing leg or even missing neutral. A real neat solution to an otherwise difficult problem.

I was unable to open that link but my SIL says they use something at pacific power that sounds similar for bad urd drops. Supposed to give full service until repairs can be made.

Here in Houston at the POCO i retired from, we would just run a temporary bypass in flexible conduit . It just layed on top of the ground.

 

[LopezBart]

Many years ago we lived in San Jose; as I was leaving for work, the construction crew across the street fired up a big Skilsaw and our lights got brighter as it started. I asked Barbie to call the power company and tell them we had a loose neutral connection on the pole. She commented later that they were quite puzzled how we knew this, but they came out that day and fixed it.

The subdivision dated from the late 1920s; poles were pretty old as well.