Would this be a weak Pole Transformer?

[jw]

I was at the tire shop the other day and had to use the restroom. While in the restroom the lights suddenly went to half brightness, and I heard their air compressor kick on in the shop. When I went back in the shop I saw the compressor, and it's quite a large beast, with a hefty motor. But that near brownout seemed excessive. It's normal for lights to flicker a little when a large motor kicks on, but these lights went to half brightness as the motor kicked on.

I know it could be wire size inside the building, or the cable from the pole to the building, but I kind of suspect the pole transformer more than the wires. The reason being that I can see the overhead wires from pole to building, and they are very thick. If it was wiring inside the building, it should not affect one 60W bulb run from 120V, when the compressor is run off 220V, which should be a breaker coming right off the mains.

This is a small town in a rural area, so the power company does not really upgrade stuff very often. Yet, this building is fed off of a 3 phase line that serves several other industrial buildings, including a large factory which closed it's doors a few years ago. Since that factory closed, there should be adequate high voltage on the supply side of the transformer, thus it would seem to me that the transformer is inadaquate or weak.....

There is no way to know the cause, since I dont work there or anything, but I'm just curious what others think.

[HeyBub]

Have you ruled out your use of the toilet?

[Ed Pawlowski]

That would be my guess also. I've seen it happen and I've seen it trip overloads too. It is like starting a motor that is jammed solid and cannot turn.

[Art Todesco]

You see stuff very different in rural areas compared to city or suburban areas. I now live in what I would call, a rural area. My house is fed by a single high voltage (5 or 10 KV) line which taps off a main line and comes up the mountain where I live. Along the way there are probably 30 or so houses/farms with transformers tapped off that line. The line then goes underground in my subdivision where only 3 or 4 houses are occupied. The transformer for my house and the neighbor (across the road) is at the roadside. I can actually see my lights blink when his AC/Heat Pump kicks in. And I see lots of other voltage drops which I can't explain. I see larger drop from things in my own house, than I ever saw living 35 miles outside a big city. I see line voltages that are nominally too high. I've actually complained to the power company about high voltage (125-128) which cause an audio amplifier to go into oscillation (probably a bad design). They said it >was< their problem and would fix it immediately. They did, I watched it come down about an hour later. But over the months, it has crept back up, I suspect, due to others upstream on the same feed, complaining about too low voltage. At least now it is only nominally running at about 120.

[RBM]

Any number of possibilities, least likely IMO would be the transformer. The compressor could be fed from a sub panel with an inadequate feeder, which also feeds the lights. A faulty unloader on the compressor could cause it, but only if the machine was wired improperly, as the overloads in it's magnetic starter should trip. Lights dimming would/could be normal when large motors start, but "flickering" is never normal, and is an indication of a loose connection.

[dpb]

On 1/22/2012 11:08 AM, Evan wrote: ...

...

Which _you_ then somehow can magically do... :(

Shoulda' stuck w/ your first conjecture, methinks. Of the responses so far, I'd think the unloader is far the most likely but it's so there's no way to have anything but a guess from afar.

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[Joe]

Given that problem I would ask for a serious discussion of power factor with the power company. IIRC, a prof in some class years ago told us that voltage and current ought to arrive together. Might need a big old PF correction capacitor to balance that long, long line,

Joe

[Evan]

I think that the unloader could be one cause, but so could a fried winding on one of the phases of the motor on the compressor, which would cause the same dramatic load issue as the motor is trying to start with 2/3rds its normal motive power...

But then again who knows, your assumptions are just as much an assumption as mine but most of us here other than the OP have at least some clue at how commercial power systems work...

~~ Evan

[gregz]

Too much unknown information. At the old house I noticed a bunch of times with dimming lights. I think the transformer fed at least 5-6 homes. When the transformer burned out, they added an extra transformer, and things were much better. I have also seen lights increase in brightness, were a load on one leg actually increases the voltage on another leg of a one phase transformer. compressor also might have been for 220 volts, really 240 and was only getting 208 volts.

Greg

[bob haller]

call the power company, they should come and take a free look, since this may be a sign of a safety issue