Weird Voltages

J

JPMPMP

Member
Location
WA state
Occupation
Electrician
Hello, I’m an electrician, and this issue has been perplexing me.

So I went to this old lady’s house and she has one of those old pushmatic panels. I tested voltage at the panel at the main lugs and I got 240v between phases and 120v between each hot and neutral with all of the breakers turned off.

As soon as turn on one of the breakers I’ll get 220v between one of the hots and neutral, and if my memory serves me correctly like 20ish v on the other hot to neutral, still getting 240ish v between phases.

When I turned that breaker off, I started turning breakers on, one by one and I was getting normal voltages (240 between phases, 120v between each hot and neutral), until I turned on like 3 breakers (each were 1p, 15a) that each distorted the voltage readings until I was getting 115v one hot to neutral and like 124v (again if my memory serves me correctly) on the other hot to neutral still getting 240ish v between hots.

I know it’s probably a loose neutral (I suspect at the meter), and my question pertains to pinpointing it and the why part. How is it possible to have normal voltages between phases and then when I turn on a breaker it makes all my voltages wonky at the panel? The breaker I turned on that gave me the 220v from 1 leg to neutral and 20v the other leg to neutral at the panel was feeding kitchen and bathroom outlets. I would think if there was a loose neutral in the outlet itself that it would show at the outlet but not mess with the hot to neutral voltages at the panel. And then the other 1p - 15a breakers that progressively showed messed up readings at the panel (with the kitchen circuit turned off) perplex me as to how that’s happening.

Any help in better in pin pointing, diagnosing and troubleshooting is much appreciated.

Thanks in advance.
 
Welcome to the forum.

JPMPMP said:
I know it’s probably a loose neutral (I suspect at the meter), and my question pertains to pinpointing it and the why part. How is it possible to have normal voltages between phases and then when I turn on a breaker it makes all my voltages wonky at the panel?
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Definitely bad neutral.

Not all breakers are heavily loaded, like the refrigerator would cause.
 
Thanks for the responses and information everyone!

The 2 or 3 other times that I’ve had a loose/floating neutral issue were basically from a tree falling on or damaging the service drop conductors somehow, and I remember having messed up voltages at the panel on the neutral, breakers on or not. So to see these readings was a bit strange.

Also most, if not everything was unplugged or removed from the residence. So there weren’t any significant loads running when I was testing.

So the recommendation should be to let the utility know there’s a floating neutral? I’m only diagnosing for a friend at church (not doing any of the repairs) and my only goal was to let her know what to expect and what the next steps are with the utility and electrical contractor she hires. Again thanks so much everyone.
 
Also, it's quite common for a POCO lineman to come out, pull the meter (thereby disabling all loads) check their L-L and L-N voltages and declare it's "all good on their side" and leave. Without current flowing across the problem (bad crimp, corroded underground lateral), a loose neutral is accidentally hidden. You must have current flowing thru a weak connection in order to have voltage drop across it.

There needs to a be a good sized L-N load, preferably only one one "side" of the service to showcase a weak neutral. Hair dryers and old toasters work well. A good experienced Lineman will have a device on the truck called "The Beast", which can load one side of the service. But not everybody has one, or knows how to use them. They just see an unloaded 120-120-240 and close the ticket.

If you are loading one side to demonstrate the problem - it's best to have all other loads off. As others have pointed out, big neutral swings cause under voltages on one side of the service and overvoltages on the other. Your appliances can get grumpy.
 
MD Automation said:
Also, it's quite common for a POCO lineman to come out, pull the meter (thereby disabling all loads) check their L-L and L-N voltages and declare it's "all good on their side" and leave. Without current flowing across the problem (bad crimp, corroded underground lateral), a loose neutral is accidentally hidden. You must have current flowing thru a weak connection in order to have voltage drop across it.
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Yep. I had that happen, and told the customer to have the POCO return and test with the main ON.

They did, and they did, and the POCO repaired the underground aluminum neutral the same day.
 
zooby said:
Yes...welcome to the forum. Just be sure to always describe your customers by their age , weight , and any physical disabilities. That helps!
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It certainly can help paint the picture. An old lady could be prone to forget details about events necessary for troubleshooting. Are you offended?
 
JPMPMP said:
How is it possible to have normal voltages between phases and then when I turn on a breaker it makes all my voltages wonky at the panel?
Click to expand...
No voltage drop when there is no current flow. Not talking about the somewhat negligible drop in conductors in normal operation but with no real loads inserted into the mix there is no voltage across any loads. Hoping you have some understanding of Ohm's law and how it works in series and parallel situations, take this example here:
1744409076331.png


In normal operation there is 120 volts across each load and they draw the watts mentioned and have resistance mentioned. Ignore for the moment the fact that the resistance across the LED lamp probably is not as linear as it would be across a pure resistance but the end numbers will still be fairly representative on why you will have a pretty higher than usual voltage across that lamp if the neutral in the circuit above were to be opened for whatever reason.

You ultimately put the two loads in a series circuit with 240 volts applied when the neutral is lost.

Details of what you end up with are:

heater plus lamp in series is 2885 + 9.6 = 2894.6 ohms
240 volts / 2894.6 ohms = .083 amps will flow in the loads when in series with 240 volts applied
(assumes resistance will remain constant)

voltage dropped across heater = .083 amps x 9.6 ohms = about .8 volts
voltage dropped across lamp = 240 - .8 = 239.2

239.2 volts x .083 amps = almost 20 watts will be dissipated by that normally 5 watt lamp,
assuming it can even handle that sort of energy

So in this case that lamp is going to see nearly all of the 240 volts, and will be drawing nearly 4 times it's normal watts. It is going to burn something out in very short time. The heater being a pretty low resistance sees very little voltage across it and doesn't even put out enough heat that you would likely even feel it, again assuming the lamp in series remains intact long enough to even allow that current to flow for any reasonable enough time to develop any significant heat in the heater.

When you have the whole house to deal with, all of "A phase" is in parallel with one another all of "B phase" is in parallel with one another, but both are in series with each other. Which ever one has the higher overall resistance is what will have a higher voltage across it. The closer the two resistances are to being equal the more "normal" operation will be as voltages will both be close to 120 volts. But every time a load turns on or off you throw the balance off from what it was and resulting voltages will shift but will always add up to the 240 that is applied.
 
zbang said:
So can a young man, or really just about anyone, myself included.


Not really, more sad that you'd try to justify the wording or that you didn't understand why that bit was irrelevant.
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I'm not justifying anything because nothing wrong was said. I'm not sure it is irrelevant. I'm not sure you are the arbiter of what is or isn't relevant. Are there any situations in your mind where such a description is warranted?
 
LarryFine said:
Yes, but it's easy to ask if any lights were brighter or dimmer than usual.
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But don't immediately jump to conclusion that the neutral is bad. It is probably one of the first things to verify though.

An open ungrounded conductor can fool you as well with lights that are brighter or dimmer than usual, but along with it comes non working straight 240 volt loads.
 
kwired said:
But don't immediately jump to conclusion that the neutral is bad. It is probably one of the first things to verify though.

An open ungrounded conductor can fool you as well with lights that are brighter or dimmer than usual, but along with it comes non working straight 240 volt loads.
Click to expand...
Yeah, the old "the lights work when the oven is on" mystery.
 
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