Cluedo

[Paul-man]

I was awoken at 2:30am by the sound of our burglar alarm going off.
It wasn't armed at the time so I was puzzled.

After frantic entering of the code, to no avail, my wife told me we'd had a "power-cut" - however the lights were on!

I went to the consumer unit, to find all breakers in the "ON" position, however, the RCD "lever" had tripped to "OFF".

After a test and reset of the RCD, followed by entering my code again on the alarm, there was golden silence.

However, there are now two things puzzling me which I hope you detectives can help me with! I'll pose the questions, then give as many extra clues as I can.


A) What tripped the RCD at 02:30 in the morning? Why did all the breakers remain on? I thought that the "offending" circuit would trip?

B) Why did the alarm go off following this power failure? We have had full power failures in the past and the alarm has never gone off as a result? (Perhaps this is one for the alarm forum, but any ideas would be great)


Extra Clues:

Shortly before bed, I burnt a mince pie in the microwave. There was a lot of smoke in the microwave and kitchen and even this morning, the kitchen stinks. The microwave would have been on "standby" at the time.

I set the dishwasher running before bed- I opened it after resetting the alarm. It hadn't finished its cycle, but everything was clean and there was no water- I assume it was in it's "drying" part of the cycle.

No Christmas lights, computers, lamps etc. were left on. The bedroom TV had been left on sleep timer, but should have gone onto standby at about 1:30am. (think it did, but was asleep!)

The broadband router and stereo were on standby. The heating was not on.

 

[electronicsuk]

Why the RCD tripped is anyone's guess. If it doesn't make a habit of it then I wouldn't worry too much.

Your alarm panel, on the other hand, is in need of a new battery. Without it, a power failure to the panel results in the external sounder going off, as it contains (another) battery to prevent it being disabled by someone simply cutting the wire that feeds it.

 

[Paul-man]

Why the RCD tripped is anyone's guess. If it doesn't make a habit of it then I wouldn't worry too much.

Your alarm panel, on the other hand, is in need of a new battery. Without it, a power failure to the panel results in the external sounder going off, as it contains (another) battery to prevent it being disabled by someone simply cutting the wire that feeds it.

Thanks Matthew.
The internal sounder was going off too. (not sure if the external one was or not)
I assume though that it must still be the backup battery in the control panel that is dead?

Paul

 

[mbga9pgf]

Its likely the dishwasher caused the trip. Why didnt your circiut breakers go? Thats not the job of the RCD. The RCD doesnt give overload fault protection, all it does is compare the phase and neutral current and trips when there is a (probably in this case) a 30 milliamp disparity. They are very sensitive.


If it happens again, it will be worth getting your dishwasher

serviced

http://www.howtomendit.com/answers.php?id=41110

Your lights didnt go off as they probably arent on the RCD protected side of your consumer unit. They are designed this way to prevent you having no lights and tripping down the stairs each and every time your RCD trips!

 

[electronicsuk]

Thanks Matthew.
The internal sounder was going off too. (not sure if the external one was or not)
I assume though that it must still be the backup battery in the control panel that is dead?

Paul

It seems odd that the internal sounder would go off too, but then again, there are internal SAB/SCB types available which contain their own siren and backup battery rather than simply being an extension speaker to the panel. Easiest thing to do would be to remove power to the panel while keeping an eye on the LEDs on the front.

 

[ericmark]

Over Christmas the lights around me have flickered a lot and there must be a fault on the DNO's system. This has tripped my RCD about 5 times. Nothing to do with faults in the house. The newer RCD's are better at not tripping but mine are 25 years old. However having had them for 25 years I know in the main they don't trip and although one may get a bout of tripping from time to time they in the main trip once every 6 months when I plug in the RCD tester to test them.

As to alarm they are limited by law to 15 minuets sounding in some areas only strobe light is permitted in outside box. There is a battery in bell/light box and one in alarm the latter normally lead acid and if the battery is faulty as said alarm will sound and of course with no battery back-up you can't disarm it.

Unfortunately they frequency that alarms go off without a break in means in real terms unless wired to a control centre they are useless. And those wired to control centres have a maintenance contract and batteries are changed as to respond costs them money. Also every room has two sensors connected to different zones and two zones have to be activated to get a response. Big problem is insurance companies who still require them to be fitted.

 

[Paul-man]

Thanks all.
I too noticed a lot of flickering at Christmas, but this was at peak times and I'd assumed it was down to high demand.
Our RCD is 20 years old, so not particularly new, so I suppose could be affected? I understand the bit about the lights being on the unprotected side of the board.

Or the dishwasher... I suppose I will play it safe and only put the dishwasher on during the day and when I'm at home. Will see what happens.

 

[JohnD]

I'm not sure about old RCDs getting more sensitive with age. In my experience, old ones are more likely to fail to trip at all (especially if they have not been regularly tested) or to refuse to reset after tripping.