Phantom Trips

[Wesley1970]

This is a question sparks have probably been asked a thousand times, but it is the first time I have asked it.

For some time now our house has been the victim of random power trips. It happens at any time of the day (morning, day, during the night), and it doesn't seem to be isolated to any individual circuit in the house. I have tried unplugging things, plugging things in etc etc, but cannot find what the cause is.

When the trips occur it is normally just the main circuit breaker that trips, rarely do any individual RCDs trip off, however, it does occasionally retrip when I switch the RCDs on individually during the reset.

I can't figure out what is causing it, and have run out of ideas of what to check. I am guessing here, that it is some kind of earth fault, but I have limited knowledge of how to go about testing for earthing faults without putting myself in the earth. I am guessing it is time to get a clever spark Sparky in to do some testing, but I am not even sure what they should be testing. Could it be a defective or outdated consumer unit? Could it be a wiring fault?

I am truly going a bit crazy trying to find the phantom trip cause.

Any advice would be apprciated.

 

[Doc Hudson]

Welcome to the forum.  It sounds like you have a perfectly functional consumer unit doing exactly what it was designed to do, protect you & your property from electrical danger.  What you refer to as RCDs I think are MCB's  and what you call the main circuit breaker is an RCD.  RCD's must remove the power in less than half a second if they detect a fault as small as 30ma passing to earth, as that is sufficient to kill and adult.  You need the RCD verified first of all, then a whole list of cable tests with various meters to get a better understanding of what may or may not be going on.  The incoming supply & earthing arrangements would also need checking. I would guess the biggest problem you have is a poor design of fuse box with just a single RCD protecting multiple circuits. Which does not comply with regulations about minimising inconvenience in the event of a fault.  Best solution is employ a competent electrician with the proper test gear to start getting some facts established.  Where about are you? we may have a forum member near who could assist? 

Doc  H.

 

[Wesley1970]

Thanks for the reply.

Sorry about the confusion with the device names. It is the main circuit breaker that goes, so the RCD. I was wondering if it could be the incoming supply problem. I will have to get someone in to do some trouble shooting. Also, I was thinking that the fuse box may need modernising, because it is very inconvenient having the whole board go each time.

I am in Horchurch, Essex. RM12 post code area.

 

[Murdoch]

Before you call a spark, I recommend you keep a log of when it trips ... this often assists in the process and can save time and money.

 

[Doc Hudson]

Thanks for the reply.

Sorry about the confusion with the device names. It is the main circuit breaker that goes, so the RCD. I was wondering if it could be the incoming supply problem. I will have to get someone in to do some trouble shooting. Also, I was thinking that the fuse box may need modernising, because it is very inconvenient having the whole board go each time.

I am in Horchurch, Essex. RM12 post code area.

You have an arrangement of fuse box that is common in a lot of properties, they were installed with that configuration due to the higher costs of RCD's compared to MCB's. It is not unsafe or dangerous, but it is not the best functional configuration due to the type of problems you are now getting. Whilst its not impossible for an external event to trip an RCD, its a more likely that your problems are 99.99% due to something on your property, connected to the fuse box, either cable or appliance or mixture of both. There could be multiple issues combined, creating sufficient earth leakage fault current, not just a single fault.

If you are seriously considering getting  your fuse box replaced, then the circuit testing that accompanies a new fuse box would cover the investigative testing of all the circuit cables required to try and identify your fault. You would still have some unknows regarding appliances, but assuming no cable faults are found during testing, you could eliminate the fuse box and all of the circuit wiring out of the equation. A full RCD board would help eliminate the confusion over which circuit has cause an RCD to trip. Some installers sell and fit cheaper dual RCD boards, but this is false economy as you can still lose half the power to the property if one RCD trips. Combined RCD and MCB's are called RCBO's 

An example of a 6 circuit full RCBO fuse box, with capacity to add four more circuits, can be seen with Screwfix part number 1460X https://www.screwfix.com/p/british-general-12-module-6-way-populated-main-switch-consumer-unit/1460x  This may or may not be any good for your particular application, but it gives a very rough idea what is available to overcome the inconvenience of intermittent earth faults, disconnecting power, when only single or double RCD board is involved.   

Doc H.   

 

[binky]

random tripping at all times of day is usually a fridge or freezer - they're the only applinces that turn on an off on there own.  RCDs tend to find faulty appliances. However, I would recommend updating the board to RCBOs - it makes a big difference to reliability and can save early replacement of appliances.

 

[Murdoch]

Up front RCD boards are the nightmares waiting to happen closely followed by dual RCD fuseboards.

RCBO boards are far better, as you would only lose 1 circuit in the event of a fault.

You may simply be experiencing accumulating leakage across all your circuits ...

Ask your friends for recommendations for sparks and get some quotes for a new board  - but be warned, no spark is going to give a fixed price to locate and fix a problem you describe.

My recent RCD investigations have concluded that:

a cat peed in an extension lead

a grand daughter turned on a redundant cable to an old pond - the cable end was exposed

a leaking radiator was letting water into a junction box

a weeping motorised value was the culprit

a laptop transformer needed to go in the bin

a chippie had put a nail into a cable

a washing machine had internal faults

....... all these had up front or dual RCD boards, meaning the customer lost all or half their circuits ..