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Our power went down yesterday afternoon (December 12). The utility posted a message on their 1-800 number with expected repair time (a few hours later), but no explanation except that ~2000 customers were affected in our suburban area (Northeast USA).
Here's the weird bit -- LED bulbs stayed on, at reduced brightness. I got out a meter and measured 16 VAC in the house. This was enough to make useful light from "dimmable" LED bulbs (happened to be GE brand). After it got dark, we could also see that incandescent bulbs were giving off a faint reddish glow.
16VAC was also enough to keep a Netgear home router/Wi-Fi box going, it must have a switcher in the wall wart that accepts a really wide input voltage range?
Called a friend on the other side of the country who is an EE (with hardware background). He didn't have a good explanation, but suggested that in the process of bringing the grid back up there might be some big voltage swings--recommended unplugging everything we could. Went out to dinner and all was restored when we got home (no damage).
He also told a story from a rural area (near CA-Nevada border) where there was a power failure that upset the normally-balanced split phase -- instead of ~120V on both sides of neutral, the power went to 80V on one side and 160V on the other side of neutral. Equipment on the high voltage side failed due to extended over-voltage, seems that surge suppressors won't deal with this much energy.
Anyone? How does the grid fail-soft?
(Score: 4, Informative) by Anonymous Coward on Tuesday December 15 2015, @06:25AM
___ ________
)( |
)( 120V R 60V
)(_____ _| <--- broken or badly corroded neutral
)( |
)( 120V 3R 180V
___)(_______|
The power company delivers the juice to your neighborhood as single-phase high voltage.
It isn't split-phase until it exits your local step-down transformer.
The usual reason for the voltage in 1 part of your house being hugely different from another part is that the neutral connection at the panel is crappy or missing.
The voltage that appears on each "phase" is then determined by the voltage divider made up of the stuff connected to each "half" of the load.
If one "half" has a whole bunch more stuff connected, that "half" will read a lower voltage.
As others have said, this doesn't appear to be the fault of the power company.
There is likely something odd going on with a neighbor's non-kosher setup.
-- gewg_
(Score: 3, Informative) by Whoever on Tuesday December 15 2015, @07:31AM
It could also be (as happened to my neighbour) a broken neutral cable from the local step-down transformer to the house. In this case, it would be the power company's fault.
(Score: 5, Informative) by LoRdTAW on Tuesday December 15 2015, @01:27PM
It's not always split phase. Some areas will feed you from a 120/208 3 phase Y using two of the three phases. Makes balancing a 3 phase high voltage feeder much easier. If the phases are labeled A, B and C, homes are connected A-B, B-C, C-A to achieve balance. The only downside is appliances expecting 240V will operate at slightly reduced power. But it usually isn't a problem.
And don't expect everything to be uniform, power companies do weird stuff. I live in south Queens a my home is powered by 120/240 true split phase. If you look at the poles, there are three wires that feed every house on the block. But when you get to either corner, you can see that the three wires met up with four wires from a 3 phase setup. This is not kosher and the lines could never be connected. So the hot legs are actually isolated with insulators on each side of the block and only the neutrals are connected. So my block is the only block in the area with true 120/240 split phase fed from a single 100KVA pole transformer. Everyone else has 120/208 off of a 3 phase Y. Why? Who knows. Maybe it was originally supposed to be multiple 120/240 feeders and they canned the idea or upgraded and our block was forgotten.
(Score: 0) by Anonymous Coward on Tuesday December 15 2015, @01:37PM
no explanation except that ~2000 customers were affected
this doesn't appear to be the fault of the power company
Uh how do you get that it is not their fault? They may have done nothing 'wrong' per se but they are quite responsible for it.
(Score: 0) by Anonymous Coward on Tuesday December 15 2015, @09:01PM
Yes, -the outage- was certainly due to the power company's stuff.
As soon as the utility came back up, all the voltages were back to normal, so a flakey neutral isn't indicated--not theirs or OP's.
The mention of 3-phase by LoRdTAW injects the possibility of a lost phase--but I have never been in a place where that is a thing in purely-residential areas[1].
I also don't recall seeing a 3-phase feed under 177V, so I dismissed that possibility.
[1] Requiring an additional sizable transformer yard and additional large wires with no monetary gain from that stuff.
Working from that dataset, my conclusion is that while the power company's feed was dead, logically, the phantom voltage was due to some cause other than the utility.
-- gewg_
(Score: 2) by sjames on Tuesday December 15 2015, @06:15PM
It can be a lot of things depending on the exact setup of the neighborhood wiring. If the power company loses the neutral, suddenly fairly simple circuits effectively become comp[lex and somewhat unpredictable. Much moreso if it's a neighborhood that has a 120/208 wye setup. For example, two lights on seperate phases are suddenly effectively connected in series across the phases instead. Turn one off, both go off. But just to confuse matters, the (disconnected) neutral is bonded to ground, so if one light is off, the other is now powered by 208v but with a high value parallel resistor and capacitor connected in series. Who knows what voltage drop it might see? (it depends on the weather, soil composition, solar activity, etc). Your TV might end up in series with the neighbor's dryer.