OT: Weird Power Problems

Though utilities in my area have been saying to the media that the grids have held up under the stress of today's high temperatures in the East, I know that at least the street adjoining mine has been browned out. My apartment building sits on an a T intersection, however, and there is power to the other street in the intersection.

Now the strange thing is, half the outlets in my apartment have full voltage, while the others are reading about 20 volts. Checked the breakers, but realized there's really no point as if they had tripped I shouldn't be reading anything. They were all fine anyhow. Just now the voltage came up to 50 volts - a compact fluorescent connected to that circuit is trying to come on. The only thing I can conclude is that this building's electrical system has some outlets connected to one power grid, and other outlets connected to a completely different grid. WTF?

Reply to
Bitrex
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It's possible that your building is being fed through multiple transformers (possibly fed from different distribution lines) and that one line is sagging more than others.

Or, it may be a split-phase problem. It's common for buildings to be fed a split phase. The "pole pig" transformer has a 240-volt center-tapped winding on the transformer... the center tap provides the "neutral", and the two ends of the transformer provide two separate 120-volt circuits, 180 degrees out of phase with one another.

The three wires (neutral, and two opposite-phase hot) come to the building. The neutral is then bonded to the electrical safety ground (I believe it's also usually grounded at the transformer), while the two "hot" wires go out to different circuit breakers and feed the individual circuits in the home.

Normally, the two circuits have nearly the same voltage on them (although in opposite phase) and you'll measure 120 volts (or thereabouts) at all of your outlets.

It sounds as if one phase being fed to your building is in trouble, while the other is holding up OK. That strikes me as unusual, and perhaps dangerous... since they're both derived from the same transformer, they should be nearly equal in value.

Significantly unequal voltages could indicate that there's a real problem in the household wiring. Possibly, there's a heat-related problem in the transformer, or in the wiring to the building, which is causing excessive voltage drop in one phase but not in the other... maybe a loose "hot" wire somewhere, with its resistance climbing as the temperature rises?

You can get other weird anomalies in this sort of split-phase system if the neutral wire breaks or comes loose. In this case, you end up with the return current for each phase-circuit having to flow through the other... the currents are forced to be equal... and this means that the voltage across each individual circuit can vary widely and can jump up well above 120 volts. If you see incandescent lights getting *brighter* when an additional load is placed on the other circuit (e.g, when a refrigerator or washing machine starts), worry about this... and call the electric company pronto. Open-neutral faults can result in significant damage to appliances, can burn out light bulbs, possibly start fires, etc.

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Reply to
Dave Platt

It's probably a phase that is out, typically the main transformer feeding the apartment has a bad phase connection or since its connected in a ring with other transformers, one of those has a phase disconnected. I've Seen melted 3kv taps on those things.

LIPA has had a steady increase in outages from this morning, they seem to be fixing them as the night goes on. Usually pole mounted transformers over heat, lights filcker, breakers pop, and life goes on.

Cheers

Reply to
Martin Riddle

This seems the most likely explanation, and if I lived in an apartment complex with many units it would make sense. But it's just a single building with two units, a duplex. My lights started going on and off a while back, and discovered it was my neighbors who were accidentally messing around with the breaker for my side - apparently their half of the duplex is suffering from the same issue. Does it make any sense to wire a single 2 unit duplex from two different distribution lines?

I thought it might be something internal to the building, but the fact that one whole neighboring street seems to be completely out while the next street is fully on, with my dwelling smack in the middle makes me think there is a connection.

Reply to
Bitrex

But wouldn't I read no voltage on the outlets if it were just a phase that was out? I've had a meter on one of the affected outlets since it went down and the voltage has been bouncing around from minute to minute, from 0 volts up to nearly 100 volts. Maybe an intermittent failure?

Reply to
Bitrex

That's possible. It's also possible a 240V device is on and feeding current into the phase that is out. Differing number of 240V devices being on and varying number of 120V loads on the dead phase would account for your readings bouncing all over the place. Art

Reply to
Artemus

It's weird- I've experienced this too. During a sumer of crappy power outages I meassured 0 volts on one leg of split phase power and 26 or something really weird like that on the other. It was so strange I broke out a Simpson panel meter to make sure my DMM wasn't broken.

I wonder if it has something to do with Scott connected transformers.

The wiring in my building is plain split phase 240.

Out in the alley, there are 3 phase high voltage lines, and it's really common to see "light" 3 phase loads delivered with one large polemount transfomer and one small one, instead of three equally sized units around here. I don't recall how things were wired up when I got the weird voltages as there's been multiple transformer fires since then, and the utility seems to have beefed things up.

Now power outages here are an all or nothing event- no strange brownouts.

Reply to
Cydrome Leader

US homes are fed with center-tapped 240VAC. One of your neighborhood lines is disconnected and the 50V you see is a 240V appliance, possibly in another home, driving the disconnected line in reverse.

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Reply to
Kevin McMurtrie

AFAIUI, apartments often use 208VAC 3-phase, which gives you 208 for the kitchen range, clothes dryer etc. and 120VAC for everything else. It does sounds like an open phase.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

As the astute Spehro has said, a lot of (most?) multifamily units of any respectable size, have a three phase feed, with 208/120 three wire feeds to the apartments.

I'd suspect that *IF* the buildings around him have the same problem, your diagnosis is correct.

If it's only in his apartment, then the problem is probably a loose connection on the breaker or feeder to his unit. The internal breaker contacts can go bad too.

He should check with his immediate apartment neighbours and see if they have the same problem.

If more than one unit has the same problem, then there may be a phase loose at the main feed to the building. The terminations can rot if they weren't tightened properly on installation.

Sometimes they go bad because of an extreme number of on/off cycles. The cycling heating on the lug can cause loosening of the conductor, which starts a vicious circle and then failure. It would be a good idea to get Building Superintendents to arrange a 'torque' check on the service feeds every so many years.

mike

Reply to
m II

Bullshit. It depends entirely on the local distribution layout.

No shit, Dip Tracy.

There are several reasons one can find elevated voltages when taking a reading of a presumed "ground conductor" or location in any system. It is flawed logic to assume only one cause.

He should call the apartment landlord and have the electrical system examined by them for proper operation.

He has no business going 'round to other units in a building asking to take meter readings on their various electrical outlets.

You are just full of enlightenment, eh?

They? What... the light switches? What "goes bad"?

Not if it was installed properly to begin with.

Your bent logic is pretty vicious.

Getting the examination to begin with is the right path, then THAT examiner *should* already be doing such a check as part of his examination. Otherwise, he is nothing more than an empty unit paint and carpet idiot that they sent out to do the work of a licensed electrician. Sounds a lot like what you must be a version of.

Reply to
Spurious Response

Yes, you normally get a divided service in your place...

Most likely every one that is using that main line is seeing the same issue.

Reply to
Jamie

Maybe where you live but not here..

Reply to
Jamie

Rural electrification incomplete? No high-rise apartment buildings at all?

Reply to
Spehro Pefhany

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