I wonder if someone could help with ideas for a strange problem that seems like it started during a recent windstorm, but maybe not.

Just about every nine minutes, the incandescent lights, seemingly all over the house and not just one circuit, will briefly dim. This is followed by a subtle flicker that goes on for maybe about 40 seconds before everything returning to normal.

The house is very quiet, without AC, and we tried unplugging any possible culprits with a compressor, such as every refrigerator and freezer. Didn't affect it. Not on any floor can we hear anything come on to explain this nine-minute cycle.

Late at night when the human electrical load is very light, this still happens just as it does during the day.

I read that tightening up any loosened screws in the panel box can sometimes help with strange flickering behaviour like this, but I don't know if that situation matches up to a regular nine-minute cycle like this.

Does this suggest anything we could look into further? Thank you!

 

Welcome to the forums.

It's very strange that it occurs every nine minutes.
Intermittent problems don't usually follow a timetable.
What do you have for heating ?

In many locations..... several homes share a common power transformer which means that it is possible to see lights flickering if your neighbor had a problem. It would be good to check with your neighbors to see if they are experiencing the same issue.

 

Do you know if your house shares it's power transformer with any other houses or is it dedicated to only your home? If your power lines are above ground you can look at the big can on the pole and see if the wires from it lead only to your house or if they go to a couple houses.

 

Oh, this was extremely helpful, thank you!

We followed the transformer wires which serves several houses. One set goes to the neighbor's standalone shop across the street. He has a large air compressor in there that is leaking air very audibly. Sure enough, about every nine minutes the compressor fires up, right on cue to dim the lights at ours. Again, thank you very much! So helpful, we didn't even have to involve the power company!

 

Not exactly on topic but if you are trying to trace the utility pole wiring, it is sometimes tricky.

Occasionally, as more pole transformers are added to meet increasing demand/load, a house might be served by a transformer that is not the closest. A stretch of pole wiring might run almost up to a transformer and be cut off and capped off, being re-fed by a transformer elsewhere. Or a stretch of wiring might be cut halfway between poles with both sets of cut ends capped off. This is sometimes hard to notice, the two halves being rewired to different transformers.

In a grid street network, pole transformer wiring (except ground wires) is not connected to form loops. Thus the uncanny cutting off of wires mentioned above. There is exactly one path from any given house to one pole transformer.

 

I would probably still give the power company a call. Though the obvious solution is to fix the leaky compressor, it seems like something else might be going on too. Even a large compressor shouldn't pull enough power to make your lights dim noticeably and especially not flicker while it's running. It's possible it's just an electrically-noisy motor, but it could also indicate a loose or corroding connection at the pole. Power dips and surges like that aren't all that good for your electronic equipment in the house.

The power company will come out at no charge and take a look. Worst case is they tell you that everything is fine.

 

Allanj -- funny -- I think we did misidentify the transformer in question, but fortunately the compressor was so loud we found it anyway.

Zorfdt -- I think you're right. It doesn't seem quite right, especially with nothing else at all running in his garage. I sent them an email ... hopefully they will come out and look.

 

You might want to file a complaint with the POCO as well. They might come out and find a problem with the transformer or that it is under sized and change it. You don't have to mention your neighbour's compressor.

 

Contacting the POCO proved helpful.

They came quickly, and said they would have given us our own transformer to the house, save the pole is too short to qualify and our neighbour's underground line installation is also somehow in the way. So they're going to upgrade the transformer that feeds us all for now. It's very nice!