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Once I had a weird electrical event in an apartment building I live in. Suddenly the Residual Current Circuit Breaker with Overload protection (I'm sure it's exactly this kind of device) in the main panel serving my apartment tripped. When I opened the panel it turned out that RCBOs for all the apartments on the same floor also tripped. That looked suspicious and so the next day I inquired with the utility company and they said that dozens of people in several buildings served by the same power substation had the same issue at the same time and the company hotline had an inrush of phone calls.

I don't get it. RCBO should trip when either there's an overload or if there's an imbalance between the phase and the neutral behind the RCBO (between the RCBO and the load). Clearly it's extremely unlikely that dozens of people had either of those at the same time, so I assume that was some external event.

What electrical event could have caused such effect?

W5VO
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sharptooth
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  • The RCBOs were probably tripping due to over-current caused by an over-voltage condition on the supply side. – MikeJ-UK Mar 14 '12 at 12:19
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    @MikeJ-UK: This is highly unlikely. I'd say I consume something like 2 kilowatts maximum which is 10 amps at 220 volts and the RCBO is rated at 50 amps so tripping it would require several times the nominal voltage which is unlikely to go unnoticed. – sharptooth Mar 14 '12 at 13:10
  • a severe over-voltage will destroy fridges before it trips breakers from supply, at least I am told this is what they worry about having happen by my friends at the power company. – Kortuk Apr 14 '12 at 06:23

5 Answers5

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Some RCDs open their contacts when the supplying net shuts off and do not automatically reconnect when the power returns. A brief black-out (say, some 10 ms) may be enough.

Your substation may have experienced such a black-out.

To be sure, you could try to find a data sheet of your particular model or do a test if you are able to safely turn off the net supplying your RCD.

If refrigerators or alarm clocks are connected to such RCDs, such a behavior would be a major annoyance. If machines, stoves or tools are connected, they may remain switched on while unpowered and you may even need this feature to avoid unintentional turn-on once the power to your home returns.

zebonaut
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Brown-outs can cause switched mode power supplies to increase their current consumption. The power supply will attempt to maintain a constant current and voltage on the output side. If the input voltage drops, then the input current will raise to compensate. Many power supplies are designed to run on both 110 V and 220 V supplies, so if you normally have 220 V and everything is running fine, you could have a 70 V brown out and those power supplies will continue providing the required output by drawing over three times the input current.

mccoyn
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    Most of the high power load is unregulated - light bulbs, space heaters, kitchen ovens - and instead will drain less current when voltage sags. The situation you describe can be likely in a datacenter, but I seriously doubt it is likely in an apartment building. – sharptooth Mar 15 '12 at 06:36
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A voltage imbalance between the phases on the supply side would cause current imbalance between the phases on the demand side, which could cause the breakers to trip. Since it happened to a lot of these breakers fed from the same substation, I expect that substation somehow experienced a glitch or short term event in one of the phases. It may be that the condition didn't persist at the substation long enough to trip something there, but some of the faster-reacting local breaker caught the event.

Connor Wolf
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Olin Lathrop
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    Each apartment is typically connected to a single phase, so the breakers are "phase+neutral" dual-pole models. – sharptooth Mar 15 '12 at 06:37
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Somewhere something connected neutral or hot to another source, either they shorted hot to ground or another device powered neutral line, like a lightning bolt could do this building wide, but this will be very dependent on the wiring.

Kortuk
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Maybe specific equipment, e.g. light dimmers, were used in your appartment, that act funny on external events. Together with above "Brown-out" idea, could be an explanation.

Bastiaan
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