sub main breaker tripped by 20+ sub sub breakers

[winayetun]

I have been living in this house for five years. From time to time, the sub main breaker (bottom-right in pic1, the RCCB breaker that is tripped in the photo) for the ground floor would be tripped. This happens during the raining season (June to October). In the dry season, there is no problem. I have identified five breakers that are at fault. When I turned them off, the sub main breaker would be tripped at most once a week. I could live with that. This season is particularly bad. More sub sub breakers are tripping the sub main breaker. This morning, the sub main breaker was tripped at around 1 am and about every 20 - 30 minutes after that. There had been two times when I flipped down all the sub sub breakers with red label (the bottom two rows) but still couldn't flip up the sub main breaker. I then played with the the breakers with yellow label and found they could also trip the sub main breaker. At that moment, I realised they were also controlled by the sub main breaker.

Thinking the sub main breaker was no good anymore (about 20 years old), I purchased a new one (the one in pic1) the first thing in the morning. It did not help at all. I have to flip down more than 20 breakers to keep the MCCB up. Now, most of the circuits are off. There is basically no power on the ground floor.

I called up an electrician friend and told him the situation. The first thing he said was "That's impossible." I said: "I thought so too but it's happening."

Any theory, however remote it might be, that could possibly explain this situation?

 

[James]

This is far from impossible.
I presume the new breaker you have fitted is the shiny white one at the bottom of the picture near the middle?

Is that an rcd? Looks like it.

It is probably not being tripped by overcurrent but by a fault to earth somewhere

It could be a faulty appliance or a damaged cable.
But my best guess is a neutral to earth fault somewhere that gets worse when the weather is wet.

It is going to need the skills of an electrician with patience and an insulation tester to track down the fault or faults.
Sadly this sounds like a job that is out of the scope of your electrician friend who says it’s “impossible “ unless there was a miss communication and they were not aware it was an rcd that was tripping.

 

[winayetun]

This is far from impossible.
I presume the new breaker you have fitted is the shiny white one at the bottom of the picture near the middle?

Is that an rcd? Looks like it.

It is probably not being tripped by overcurrent but by a fault to earth somewhere

It could be a faulty appliance or a damaged cable.
But my best guess is a neutral to earth fault somewhere that gets worse when the weather is wet.

It is going to need the skills of an electrician with patience and an insulation tester to track down the fault or faults.
Sadly this sounds like a job that is out of the scope of your electrician friend who says it’s “impossible “ unless there was a miss communication and they were not aware it was an rcd that was tripping.

Thanks for the reply. Yes. That's the new one, no red label. It's an RCD and I didn't mention that to my electrician friend.

I think the RCD is tripped by ground fault too. Overloading should trip the sub sub breaker.

I have also suspected ground fault ever since the tripping problem started few years back. However, I cannot explain why more than 10 breakers join the "rebellion" overnight. Surely one faulty appliance would not cause other breakers to cause tripping, would it? I mean if an appliance on breaker A has ground fault, would it cause breaker B to trip the sub main breaker? If not, how come so many circuits all have developed ground fault overnight?

The breakers with yellow label had never had any problem before and suddenly, overnight, half of them are causing the RCD to trip. How could this be? Overnight?

 

[James]

Neutral to earth faults can trip an rcd even when the breaker to the appliance or circuit with the fault is turned off.

This requires some proper fault finding it can’t be done by elimination of circuits by turning off breakers.

 

[winayetun]

Thanks for the reply. OK, that's beyond my limited knowledge on electricity, breakers, and circuits but let me guess. All the neutral wires are connected to one bus, all the grounding wires to another. If there is a neutral to ground fault, it seems more than one breaker could trip the RCD because the current from a good circuit eventually ends up in the neutral bus and from there it could find its way to cross to the faulty grounding wire and trip the RCD. Is this correct? If this is correct, it seems all breaker would trip the RCD, not just the five I turned off before.

 

[James]

Thanks for the reply. OK, that's beyond my limited knowledge on electricity, breakers, and circuits but let me guess. All the neutral wires are connected to one bus, all the grounding wires to another. If there is a neutral to ground fault, it seems more than one breaker could trip the RCD because the current from a good circuit eventually ends up in the neutral bus and from there it could find its way to cross to the faulty grounding wire and trip the RCD. Is this correct? If this is correct, it seems all breaker would trip the RCD, not just the five I turned off before.

Yes, you are pretty close there. Any load on any circuit can increase the voltage on the neutral line and if some leaks back to ground then it causes an imbalance that is seen as a fault by the rcd.