# Partial power outage..



## GarageBoy (Feb 26, 2006)

Well, right now, I have a partial power outage. Theres power in select rooms of my house, same thing is happening with my neighbors..so I'm typing by RR 2AAA light right now. Anyone guess what could be the cause?


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## kbog (Feb 26, 2006)

Weird. Might be a good idea to unplug electronics to protect from a surge...


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## FLASHLIGHTMAN (Feb 26, 2006)

I would guess that there is a fuse blown at the transformer.

It sounds like to me that you are only getting 1 leg of the 220 that comes into your house. The reason you have select rooms on right now is that your service panel is split (every other breaker) to one side of the 220 that comes in. It takes both legs to get the 220 volts, but if one leg is down, you would still have 110 on the live side. 

I would only guess this is true since your neighbors are experiencing the same thing. If it had been you only, I would say it was in YOUR main panel.

Good luck! At least your computer is still up!


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## Morelite (Feb 26, 2006)

The transformer has a secondary output line dead.


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## Wireman (Feb 26, 2006)

FLASHLIGHTMAN said:


> I would guess that there is a fuse blown at the transformer.
> 
> It sounds like to me that you are only getting 1 leg of the 220 that comes into your house. The reason you have select rooms on right now is that your service panel is split (every other breaker) to one side of the 220 that comes in. It takes both legs to get the 220 volts, but if one leg is down, you would still have 110 on the live side.
> 
> ...


 HEY! That's what I was gonna say!


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## jayflash (Feb 26, 2006)

Luckily for you & your neighbors that the neutral didn't open or you may have zapped some of your equipment.


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## Morelite (Feb 26, 2006)

I would be good to make sure all 220 volt devices like dryers, range, over, well pump, etc is turned off or disconnected. If one of those happens to be "on" it could feed the electricity from the powered leg (side of your panel) to the dead leg and cause a "brownout" effect on the devices connected to the dead side.


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## GarageBoy (Feb 26, 2006)

Thanks! Theres no 220V inside my building, so I'm safe..I think, power is now restored


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## Perel (Feb 26, 2006)

If this happens again, turn off your power at the main breaker immediately. Then call your electric utility's emergency number and report the outage. Don't turn it back on until they've fixed it. Indeed, you are VERY lucky the neutral didn't open. That can and does cause fires.. and if one leg is out, I wouldn't trust the neutral either. If your power is doing something weird, shut it off and report it - that's the safest thing to do.

The symptoms of an actual open neutral are some lights dimmer than usual and others BRIGHTER than usual. If you ever see that, turn the power off IMMEDIATELY!


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## GarageBoy (Feb 27, 2006)

Thanks for the warning!


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## bexteck (Feb 27, 2006)

My EE professor just told us a story the other day where the neutral line fell out of it's clamp in his breaker box because the electrician didn't tighten it down, and that he ended up testing 3V on one side of the house and 237V on the other side, which of course meant one side of the house didn't work and all the electronics which were connected to the other side burned up because they experienced double their rated voltages.

Can someone explain what exactly the neutral line does to keep these two 120V lines at their appropreate voltages?


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## yuandrew (Feb 27, 2006)

I had the same thing happen as well in my house shortly a few years after we moved in. Electrician said it was a bad neutral connection inside the breaker panel. Dad later told me the red wire probably shorted to the neutral

Around 240 volts went to one part of the living room and a very low voltage went to the other part (dim lights in half the house and really bright lights that lasted for a few seconds in the other half). Fried two TVs, a stereo, VHS tape rewinder, my Nintendo, a VCR, Aquarium pump, three fluorescent light ballasts, and popped a few incandescant bulbs.


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## turbodog (Feb 27, 2006)

GarageBoy said:


> Thanks! Theres no 220V inside my building, so I'm safe..I think, power is now restored



So...... you don't have a clothes dryer or an oven/stove?


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## CLHC (Feb 27, 2006)

At least you're prepared with some light right?


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## GarageBoy (Feb 27, 2006)

Again..220 inside my building..
Gas Dryer..Washer/Stove all use 120V


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## GarageBoy (Feb 28, 2006)

Wait, when the neutral blows..doesn't the electricity cease to flow?


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## Navck (Feb 28, 2006)

Not with AC power, it just needs two live wires.


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## Perel (Mar 1, 2006)

Most residential power in the US is provided as single phase 220V with a center tapped neutral. This means that you can draw 220V between the two hot legs, or 110V from one leg to neutral. So long as the neutral is properly connected, it will keep the voltage on each leg approximately correct. (bextech, the neutral carries the *difference* in current between the two hot legs. If the two legs are each drawing the same amount of current, there is no current carried by the neutral. As soon as they fall out of balance, the neutral carries as much current as is needed to keep the two legs in balance. I can dig out the mathematical explanation if you'd like.)

Take away the neutral's connection to the power company's transformer, and you don't have anything holding each leg to 120V. The one that needs more power will actually get LESS, and the one that needs less power will actually get MORE. This is a Very Bad Thing. If this happens, 220V appliances will continue to work fine, because they are drawing hot to hot and not using the neutral. (This is what yuandrew described exactly.)

So why don't we use hot/hot all the time? Because it's more expensive. Center-tapped single phase is a very efficient way to provide 110V service while still having 220V available for heavy loads where the wire size required at 110V would be even more expensive. On ships, for instance, where there is no ground reference to tie neutral to, delta power (hot/hot) is used. That would be two 60V hots together forming a 120V supply, just like the two 110V hots in residential service together form a 220V supply.

One more complication - you're in NYC. Many older apartment buildings actually use commercial three-phase power. With that setup, you have a neutral and THREE hots that are out of phase with each other. You can develop 110V from any one hot to neutral, or 208V between any two hots. The advantage of this system is that it's much more efficient when all three hots are attached to a large motor. For instance, elevators work much better on three-phase power.

Note that I am talking about US/Canada power here. It's done differently other places; the UK, for instance, has a particularly unusual approach.


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