# Circuit Breaker Tripped In The Night - Why?
**URL:** https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734
**Category:** Factual Questions
**Created:** [February 13, 2009, 8:05pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734 "2009-02-13T20:05:51Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Gleena](https://boards.straightdope.com/u/Gleena)
#### Post date: [February 13, 2009, 8:05pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/1 "2009-02-13T20:05:51Z")
Hi,
**Subtitled…do I panic and call my electrician, because this is my house and not a rental?**
Sometime between say 2am and 6:30am the main circuit breaker switch tripped. Things running at the time were one fan, two clock radios (just telling time), fridge, outside light and the residual power two computers draw when “shut down” - I don’t own a microwave, and I think the TV draws a trickle of power, although I can’t remember the last time we had it on.
It was raining and blowing wind.
Also, it shut down the _main_ switch, not a specific circuit as has done once or twice in the past when I plugged in everything I own on top of having the aircon running (aircon was NOT running last night.)
Can an external source (like a power surge) trip your breaker? Does it have to be something inside the house? Given what was on, what could have possibly tripped the whole house circuit?
Should I call my electrican?
Thanks!!
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### Author:  [@ouryL](https://boards.straightdope.com/u/ouryL)
#### Post date: [February 13, 2009, 8:40pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/2 "2009-02-13T20:40:21Z")
[We ALL know the reason!🆒](http://robojapan.blogspot.com/2008/11/ufos-blamed-for-uk-power-outage.html)
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### Author:  [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)
#### Post date: [February 13, 2009, 8:51pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/3 "2009-02-13T20:51:48Z")
You may have water running into your main breaker panel. It could be something else too.
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### Author:  [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)
#### Post date: [February 13, 2009, 9:22pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/4 "2009-02-13T21:22:35Z")
Definitely call an electrician. It takes something pretty dramatic to trip a main breaker - normally an overload on an individual branch circuit will trip only that one 15 or 20 amp breaker.
My money would be that water got into the panel and shorted out the main bus, given the weather you described. If you’re lucky, it just needs to be dried out and the leak found and sealed. However, water damage often is bad enough that the panel will need to be replaced.
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### Author:  [@astro](https://boards.straightdope.com/u/astro)
#### Post date: [February 13, 2009, 10:37pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/5 "2009-02-13T22:37:26Z")
Main breakers tripping is unusual. Get it looked at. An incoming surge can trip a breaker but if its big enough to do that will usually fry lots of other stuff in the house. If nothing is blown it’s probably a panel, breaker or in house issue.
Also bear in mind if the breaker switch itself is old or corroded enough it can trip spontaneously with no overload issues involved.
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### Author:  [@Magiver](https://boards.straightdope.com/u/Magiver)
#### Post date: [February 13, 2009, 10:48pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/6 "2009-02-13T22:48:30Z")
I’ve never personally seen a breaker trip from a spike/loss of electricity but it might be possible. It could be external at the transformer so the first thing I would look at is the voltage reading from BOTH lines coming into the house. Then I would look for something obvious like a water leak or a damaged ground wire.
Unless you know something about electricity and wiring I would call an electrician for peace of mind.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [February 13, 2009, 10:54pm UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/7 "2009-02-13T22:54:51Z")
> [@Magiver](#):
>
> It could be external at the transformer…
No, it couldn’t. Faults upstream from the main breaker will trip power company circuit breakers either at the pole or, in severe cases, at a subdistribution station. If the main breaker has tripped due to an overcurrent fault, then the fault is inside.
Voltage surges and outages never trip thermal circuit breakers, but they can pop ones with a magnetic trip. The vast majority of residential main breakers are thermal only.
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### Author:  [@Magiver](https://boards.straightdope.com/u/Magiver)
#### Post date: [February 14, 2009, 12:39am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/8 "2009-02-14T00:39:24Z")
> [@Q.E.D](#):
>
> No, it couldn’t. Faults upstream from the main breaker will trip power company circuit breakers either at the pole or, in severe cases, at a subdistribution station. If the main breaker has tripped due to an overcurrent fault, then the fault is inside.
>
> Voltage surges and outages never trip thermal circuit breakers, but they can pop ones with a magnetic trip. The vast majority of residential main breakers are thermal only.
You probably know more than I, but if the voltage is low, won’t that create a draw against the demanded load? I had problems with low voltage when I lived in a trailer court and it caused a lot of damage to appliances in the park. Can’t remember if it tripped any mains. What would a water heater do to a breaker if the voltage drops?
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### Author:  [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)
#### Post date: [February 14, 2009, 1:25am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/9 "2009-02-14T01:25:36Z")
> [@Magiver](#):
>
> What would a water heater do to a breaker if the voltage drops?
In simple terms, the water heater presents a resistance to the incoming power, if the voltage drops it will merely draw less current. Circuit breakers trip for overload (too much current over a time span) or short circuit (way more current over a much shorter time span). There are devices to detect undervoltage conditions but a typical house wouldn’t be equipped with that type of protection.
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### Author:  [@cornflakes](https://boards.straightdope.com/u/cornflakes)
#### Post date: [February 14, 2009, 2:49am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/10 "2009-02-14T02:49:15Z")
This may be a dumb question, but what brand of panel is it? I don’t know about Australian electrical stuff, but the USA had a problem with Federal Pacific panels and breakers (Of course then, the problem was that the panels fell apart and that the breakers wouldn’t trip, not that the breakers tripped all the time…)
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### Author:  [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)
#### Post date: [February 14, 2009, 2:59am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/11 "2009-02-14T02:59:32Z")
If you trip one of those breakers you have a real big problem. [Some interesting reading on FPE panels.](http://www.inspect-ny.com/fpe/fpepanel.htm)
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### Author:  [@Gleena](https://boards.straightdope.com/u/Gleena)
#### Post date: [February 14, 2009, 3:23am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/12 "2009-02-14T03:23:07Z")
> [@cornflakes](#):
>
> This may be a dumb question, but what brand of panel is it? I don’t know about Australian electrical stuff, but the USA had a problem with Federal Pacific panels and breakers (Of course then, the problem was that the panels fell apart and that the breakers wouldn’t trip, not that the breakers tripped all the time…)
I don’t know, I’ll have a look.
I will call the electrician, as the panel is undercover (under a balcony on the house) and is probably not wet. I mentioned the weather thinking it might have come from the electricity coming into the house, and the weather might have caused a power surge or something. It’s brand new, I had the last one replaced as it didn’t have proper fuses or breakers, but the old ceramic things you had to replace the wire in if the fuse blew. Ugh.
It’s been on all day since with a bigger load and no problems, I checked and it doesn’t feel warm or anything.
Thanks for the advice, I’ll call the sparky on Monday.
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### Author:  [@Gleena](https://boards.straightdope.com/u/Gleena)
#### Post date: [February 14, 2009, 3:24am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/13 "2009-02-14T03:24:11Z")
> [@HongKongFooey](#):
>
> In simple terms, the water heater presents a resistance to the incoming power, if the voltage drops it will merely draw less current. Circuit breakers trip for overload (too much current over a time span) or short circuit (way more current over a much shorter time span). There are devices to detect undervoltage conditions but a typical house wouldn’t be equipped with that type of protection.
It’s a gas water heater, though, so that couldn’t be it anyway.
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### Author:  [@Magiver](https://boards.straightdope.com/u/Magiver)
#### Post date: [February 14, 2009, 3:43am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/14 "2009-02-14T03:43:14Z")
> [@HongKongFooey](#):
>
> In simple terms, the water heater presents a resistance to the incoming power, if the voltage drops it will merely draw less current. Circuit breakers trip for overload (too much current over a time span) or short circuit (way more current over a much shorter time span). There are devices to detect undervoltage conditions but a typical house wouldn’t be equipped with that type of protection.
There is a relationship between load, voltage and wire size. As the voltage goes down, the required wire size for a given load goes up. It would be like adding a larger load to an existing circuit. If you’ve ever dropped a 20 amp load on a 15 amp circuit it will trip it easily. In this situation, it would still only trip the circuit it’s on, not the main. That’s been my experience with wiring boxes up and distributing loads.
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### Author:  [@Magiver](https://boards.straightdope.com/u/Magiver)
#### Post date: [February 14, 2009, 3:45am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/15 "2009-02-14T03:45:08Z")
> [@Gleena](#):
>
> It’s a gas water heater, though, so that couldn’t be it anyway.
I can’t think of anything that would trip the main except a major short or a partial loss of the ground. Its possible you have an ex-mouse in the breaker box but you’d smell that. You said you weren’t running the air. is there a chance it tried to kick on? I had a central unit grenade on me and it may have taken out the main come to think about it. It was a dead short situation which took out a hard fuse with it so once the breaker was switched back on there was nothing to trip it.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [February 14, 2009, 4:06am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/16 "2009-02-14T04:06:32Z")
> [@Magiver](#):
>
> There is a relationship between load, voltage and wire size. As the voltage goes down, the required wire size for a given load goes up. It would be like adding a larger load to an existing circuit.
No, it doesn’t work this way. For a given device, the load impedance is more-or-less constant. Current drawn is equal to the applied voltage divided by the load impedance. Thus, if the supply voltage drops, the load current drops proportionally. Appliances designed for use on 240 V lines need less current (and therefore thinner wires) than their 120 V cousins because their loads have double the impedance.
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### Author:  [@Magiver](https://boards.straightdope.com/u/Magiver)
#### Post date: [February 14, 2009, 4:25am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/17 "2009-02-14T04:25:03Z")
> [@Q.E.D](#):
>
> No, it doesn’t work this way. For a given device, the load impedance is more-or-less constant. Current drawn is equal to the applied voltage divided by the load impedance. Thus, if the supply voltage drops, the load current drops proportionally. Appliances designed for use on 240 V lines need less current (and therefore thinner wires) than their 120 V cousins because their loads have double the impedance.
I’m not arguing here, but what happens when you drop something with a heavy load such as car starter on a 6 volt battery assuming the wire for the 12 volt system is the same. Doesn’t it create more heat from undersized wiring?
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [February 14, 2009, 4:31am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/18 "2009-02-14T04:31:41Z")
> [@Magiver](#):
>
> I’m not arguing here, but what happens when you drop something with a heavy load such as car starter on a 6 volt battery assuming the wire for the 12 volt system is the same. Doesn’t it create more heat from undersized wiring?
Well, certain types of heavy-duty motors are kind of a special case. If you heavily undervolt them, they will either turn very slowly or not at all; both of these conditions can cause rotor core saturation, resulting in large current draws. But for normal household loads the I = V/R relationship generally holds.
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### Author:  [@Gbro](https://boards.straightdope.com/u/Gbro)
#### Post date: [February 14, 2009, 5:16am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/19 "2009-02-14T05:16:30Z")
I would look to the fridge as a possible cause, although that should trip a circuit not the main.
You posted,
> [@](#):
>
> It was raining and blowing wind.
If the fridge was running and you had a temporary power outage that reset itself as our systems do. the fridge compressor would be loaded and not start as it needs several minuets to bleed the pressure off. Most refrigerators will just cycle the overload until they bleed down but who knows ??
There is a test that can be done but I would leave that to an electrician.
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### Author:  [@Gleena](https://boards.straightdope.com/u/Gleena)
#### Post date: [February 14, 2009, 5:19am UTC](https://boards.straightdope.com/t/circuit-breaker-tripped-in-the-night-why/485734/20 "2009-02-14T05:19:44Z")
> [@Magiver](#):
>
> I can’t think of anything that would trip the main except a major short or a partial loss of the ground. Its possible you have an ex-mouse in the breaker box but you’d smell that. You said you weren’t running the air. is there a chance it tried to kick on? I had a central unit grenade on me and it may have taken out the main come to think about it. It was a dead short situation which took out a hard fuse with it so once the breaker was switched back on there was nothing to trip it.
No, that’s why I’m confused - it’s a split system in each main room, none of them were on and none of them are on a timer or thermostat.
No dead rats (more likely than mice here).
Only the main breaker tripped, non of the…er…sub breakers? Individual circuits. I’m a bit stupid about this stuff, sorry.
I’m really stumped, though, as there’s no obvious cause.
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