Possible loose neutral issue

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dhalleron

dhalleron

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Location
Louisville, KY
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Master Electrician/Senior Fire Alarm Technician
Long story, so pass if you're not in for a long read.

Probably a ton of posts on this but anyways...

My neighbor has a 1950s house with a 60 amp service. Someone replaced the panel with a 100 amp main breaker panel.

Neighbor told me the lights were blinking when the central air came on. They wanted the top half of the service upgraded anyway and I assumed that would fix it. I never actually saw any blinking.

After I upgraded top half of service to 100 amps they said lights still blinked. I did find a loose wirenut on the hot side in one box that caused a living room lamp to blink when I moved the wirenut. Didn't fix the issue.

At the main breaker I measure right at 240 volts and 120 to both neutrals. At the living room lamp I measured 117 volts. When we turned on microwave oven the voltage went up to 119 volts. Didn't check to see if they were on opposite phases or not.

The garage is on it's own 2 pole 30 amp circuit with a sub panel. They tell me lights blink there too but I didn't see it.

I'm thinking since blinking is on different circuits and all connections at panel and meter are tight, it must be a power company issue. Will be calling them tomorrow.

Anything different I should have done? Any magic blinking light troubleshooting techniques I need to be aware of?

Thanks for reading.





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dhalleron said:
Neighbor told me the lights were blinking when the central air came on.

I'm thinking since blinking is on different circuits and all connections at panel and meter are tight, it must be a power company issue. Will be calling them tomorrow.
Click to expand...

The power company is the right way to go. Let them put a load on the service with the "beast".

It doesn't have to be a neutral to cause the lights to blink. One of the hot cables could have a bad splice that heats up because of the AC load.
 
How long is the service drop? If it's a long ways and the wires are minimum for the service, you could just be dealing with voltage drop. Starting surges from motor loads starting are a common source of problems. POCO should be able to tell if that's the problem, or the transformer may have too much load if it's shared between several customers. They should measure voltage at the transformer and at the meter under heavy load to see if there's a voltage loss. That's what a beast is for. Fairly common but often hard to convince the POCO to upgrade the service. We have added transformers and split the customers many times, especially in older areas where the original service was inadequate for the increased load of all the "new-fangled electrical gadgets". Transformer overloading is usually seen as blinking lights when you are not starting anything yourself that would cause it but the neighbor might be.
 
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Other possibilities lie in the compressor itself. Aging/malfunctioning start capacitor. Debris-laden vent fins. Clogged refrigerant line. Over-pressurized refrigerant line.
 
You said it's central AC, so assuming it's 240v, a neutral problem wouldn't cause a load variance between the phases, so voltage shouldn't seesaw between them with 240v loads.

Did the the blinking lights problem exist before the panel was changed? If so then I agree with previous suggestions that the relatively large central air startup load on a system with relatively small service wire is causing the voltage fluctuation.

House dates to the 50's....is any of it aluminum wire?
 
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It may be fixed but time will tell.

I found the main lugs on the existing panel had some corrosion. I cleaned it up and put on some deox.

Customer said no blinking last night or this morning.

There is no aluminum wire that I have seen in this house.

The poco transformer appears to feed about 10 houses and this house is near the end of the run but not last. A neighbor at the same connection point reported no blinking.

Will give it a few days and if it happens again I will call poco.

Thanks for the input. Been doing this a lot of years but only part time the last 25 years or so. Always helps to get other opinions.

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Forgot to mention the lights did blink before the upgrade, I just never saw it.

The AC unit is fairly new on a 25 amp breaker but could still be a problem.

Waiting for now.

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I always tell customers that some amount of flicker upon start-up of A/C or electric heat is normal, as long as there is no other issue from it.
 
dhalleron said:
It may be fixed but time will tell.

I found the main lugs on the existing panel had some corrosion. I cleaned it up and put on some deox.

Customer said no blinking last night or this morning.

There is no aluminum wire that I have seen in this house.

The poco transformer appears to feed about 10 houses and this house is near the end of the run but not last. A neighbor at the same connection point reported no blinking.

Will give it a few days and if it happens again I will call poco.

Thanks for the input. Been doing this a lot of years but only part time the last 25 years or so. Always helps to get other opinions.

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Click to expand...
I'm guessing it is mostly a problem with lights dimming when compressor is starting, and that you are experiencing voltage drop during this starting period because of the length of the run and size of conductor's.

Problem is POCO may come out and check running voltage and say it is within range of what they are required to deliver and won't do anything about it.
 
Did you verify that neutral is not bonded to ground at the subpanel in the garage or anywhere else but the main panel?

As long as that's not the case I would be asking for The Beast too and expect you'll find a weak ground or neutral bond at the meter.


dhalleron said:
Long story, so pass if you're not in for a long read.

Probably a ton of posts on this but anyways...

My neighbor has a 1950s house with a 60 amp service. Someone replaced the panel with a 100 amp main breaker panel.

Neighbor told me the lights were blinking when the central air came on. They wanted the top half of the service upgraded anyway and I assumed that would fix it. I never actually saw any blinking.

After I upgraded top half of service to 100 amps they said lights still blinked. I did find a loose wirenut on the hot side in one box that caused a living room lamp to blink when I moved the wirenut. Didn't fix the issue.

At the main breaker I measure right at 240 volts and 120 to both neutrals. At the living room lamp I measured 117 volts. When we turned on microwave oven the voltage went up to 119 volts. Didn't check to see if they were on opposite phases or not.

The garage is on it's own 2 pole 30 amp circuit with a sub panel. They tell me lights blink there too but I didn't see it.

I'm thinking since blinking is on different circuits and all connections at panel and meter are tight, it must be a power company issue. Will be calling them tomorrow.

Anything different I should have done? Any magic blinking light troubleshooting techniques I need to be aware of?

Thanks for reading.





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Click to expand...
 
Redwood Infrared said:
Did you verify that neutral is not bonded to ground at the subpanel in the garage or anywhere else but the main panel?

As long as that's not the case I would be asking for The Beast too and expect you'll find a weak ground or neutral bond at the meter.
Click to expand...

A poor or missing neutral connection will cause lights to dim and brighten, for as long as a significant 120v load is present. The OP's condition was lights that briefly dimmed when the 240v AC started. 240v loads don't utilize the neutral and do not have any effect if the neutral is weak or missing.
 
Since I cleaned the corrosion I found under the lugs of the main breaker 2 days ago they tell me the blinking and dimming has stopped.

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dhalleron said:
Since I cleaned the corrosion I found under the lugs of the main breaker 2 days ago they tell me the blinking and dimming has stopped.

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Click to expand...

Sounds like "mission accomplished".
 
Sometimes I make things seem harder than they are.

They have honey bees, so for my extra effort I am getting some local honey. I wouldn't take extra money because I should have caught the original problem during the service upgrade.
gadfly56 said:
Sounds like "mission accomplished".
Click to expand...

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