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Old 02-11-2009, 10:19 AM   #1
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Breaker tripped after power outage. What's up?


Last night the power at our house went our or blipped enough to kill the power - Microwave was flashing 00:00 this morning.

At some point during the night the breaker on just one circuit switched off. The circuit is, I admit, taxed to the max, load-wise. The circuit has several surge protected appliances connected to it (computer, TV/Audio, and a fish tank - I know, I know...).

What happened? Did the breaker trip when the power came back on? Could this indicate a problem with the breaker itself?

Thanks for your thoughts. I am going to run some new romex and give the computer (and dining room) its own branch circuit on the 21st. So, I'm not really looking to troubleshoot, just curious about what happened and would love to hear some thoughts.

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Old 02-11-2009, 10:35 AM   #2
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Breaker tripped after power outage. What's up?


The breaker couldn't stand the high inrush current when the power returned and everything came on all at once, rather than the loads being turned on sequentially like a person would do (and so the load on the breaker is ramped up slowly).
The breaker can handle the steady-state current.

The switchmode power supply in a computer has very high inrush current, as do fridge and HVAC compressors. Less so for TVs and microwaves, I think.

Likely there is no problem.
I guess you could duplicate the effect by turning off the breaker for a minute or so and then trying to turn it back on. It shouldn't allow you to because it will see the same high inrush current, again.

PoCo has the same problem after a widespread blackout. Everybody's fridge has warmed up and is just waiting for the power to return so they all can pull an enormous cumulative startup current, and then PoCo's breakers will all trip (again).

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Old 02-11-2009, 10:53 AM   #3
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Breaker tripped after power outage. What's up?


Also surge protectors work by shorting the wires if the voltage is too high. If there was a voltage surge, your surge protectors may have activated and this may have tripped the breaker (a good thing!).
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Old 02-11-2009, 03:01 PM   #4
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Breaker tripped after power outage. What's up?


Maybe a voltage surge occurred?
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Old 02-11-2009, 05:25 PM   #5
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Breaker tripped after power outage. What's up?


It is good thing, circuit breaker tripped. That is why it is there, in order to protect your equipment connected to thet circuit
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Old 02-11-2009, 05:45 PM   #6
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Breaker tripped after power outage. What's up?


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Originally Posted by mpj111 View Post
It is good thing, circuit breaker tripped. That is why it is there, in order to protect your equipment connected to thet circuit

Actually the breaker was designed for circuit protection, but it also aids in protecting equipment in a way.
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Old 02-11-2009, 05:51 PM   #7
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Breaker tripped after power outage. What's up?


Was everything on when this happened?
If the load wasn't near Max it should not have tripped
Could just be the surge
I have a dedicated circuit for my fish tank - pretty big tank
I don't want my breaker kicking out due to something plugged into another outlet. It doesn't take long for fish to die without water circulation/air
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Old 02-11-2009, 08:37 PM   #8
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Breaker tripped after power outage. What's up?


Wasn't a GFCI breaker, was it? Those will often trip when power returns.
If you have computer equipment on the branch, using surge protection, you may have indeed received a surge on the line, and the equipment caused a momentarily very high current when the power returned. I would check all of your surge equipment carefully. After activation, they may need to be replaced. Usually, there is a green (or other color) LED that is lit when protection is good. If the light is out, replace the device.

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Old 02-12-2009, 09:57 AM   #9
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Breaker tripped after power outage. What's up?


Thanks for the input.

Not a GFCI breaker, just a regular one. I'm betting when the power came back on everything drawing at once might be over current for the circuit.

Under what mechanism would a surge protector trip a breaker?

I WILL check all the surge protectors - I've had one fail after a surge before. Is there any way to test ones that do not have the indicator light?
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Old 02-12-2009, 11:03 AM   #10
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Breaker tripped after power outage. What's up?


Breakers trip in milliseconds, electronic stuff dies in microseconds, surge protectors work in nanoseconds.
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Old 02-12-2009, 11:35 AM   #11
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Breaker tripped after power outage. What's up?


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...Under what mechanism would a surge protector trip a breaker?...

Surge protectors use a device called a Metal Oxide Varistor or MOV.

When a voltage reaches a certain level, these devices "turn on" or short the two connections. These will typically short all connections in the event of a surge. Hot to neutral, hot to ground, neutral to ground.

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http://en.wikipedia.org/wiki/Varistor
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Old 02-12-2009, 11:45 AM   #12
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Breaker tripped after power outage. What's up?


Quote:
Originally Posted by Billy_Bob View Post
Surge protectors use a device called a Metal Oxide Varistor or MOV.

When a voltage reaches a certain level, these devices "turn on" or short the two connections. These will typically short all connections in the event of a surge. Hot to neutral, hot to ground, neutral to ground.

More...
http://en.wikipedia.org/wiki/Varistor
The only time a surge protector should cause the breaker to trip is if it destroys itself in the process of protecting the load. While MOV's usually just open up and smoke a bit when they are destroyed, they can also cause a short, which would trip the breaker.

As for the surge protectors without indicator lights: Replace them with newer models that do have the indicators, since there is absolutely no way to know whether the device is still protecting your equipment if it does not have an indicator.

That said, I took apart a single-outlet surge unit that I used for my microwave when the indicator LED went out.
What I found was a MOV, and the LED, which was connected through a resistor, but without a diode across the line. The diode burned out, but there is no way of knowing whether the MOV is still working. In any case, the device needs to be replaced.

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Old 02-12-2009, 12:04 PM   #13
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Breaker tripped after power outage. What's up?


Most surge suppressors have thermal fuses before and after the varistor. These will open the circuit when the temperature reaches dangerous conditions. Some units will use these fuses to cut power to your equipment in the case of a prolonged overvoltage.
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Old 02-12-2009, 05:42 PM   #14
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Breaker tripped after power outage. What's up?


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Most surge suppressors have thermal fuses before and after the varistor. These will open the circuit when the temperature reaches dangerous conditions. Some units will use these fuses to cut power to your equipment in the case of a prolonged overvoltage.
Those would be the more expensive ones. The ones without the indicator lights just have a circuit breaker, but I doubt it would trip before the branch breaker trips.
It might be interesting to open up one of the expensive Radio Shack strips I have. If I can do it without damaging the device, I might.

FW
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Old 02-12-2009, 07:56 PM   #15
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Breaker tripped after power outage. What's up?


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Originally Posted by KE2KB View Post
Those would be the more expensive ones. The ones without the indicator lights just have a circuit breaker, but I doubt it would trip before the branch breaker trips.
It might be interesting to open up one of the expensive Radio Shack strips I have. If I can do it without damaging the device, I might.

FW

I cant take apart any of mine...no way to. I use hospital grade receptacle tvss's. I need two more...it has taken 1 1/2 weeks for the company to get them in stock.

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