Nuisance Tripping

[ROMSTER]

I have read several posts about similar issues and want to get some thoughts on the problem I have.

Downstairs 13a socket ring is wired through a brand new RCCB and fuse board. The RCCB keeps randomly tripping (has done since it was installed) and recently we returned from a holiday to find freezer defrosted etc and boiler off. Thats rather spurred me into action

The RCCB also trips when using an iron on that circuit - so we can 'force' it to trip.

However, it also trips when there is no incremental load on the circuit - only fridge/freezer and boiler were on the circuit when we went on holiday so no 'event' to make it trip - unless perhaps boiler or fridge coming on at certain times of day overloads things

It sometimes goes for a week without tripping - sometimes every few days and there is no pattern.

Could we have a faulty/over sensitive RCCB unit? Or is there something else that might be causing a live leak in the system - and how do you check this. The whole circuit was approved by a NICEIC contractor when it was put in

As you can imagine resetting clocks and all that nonsense is getting very boring

 

[ColJack]

culprits to check..

outside lights / sockets / JB's / cabling.. if cable or boxes are damaged then water / damp can get in and cause leakage..

watery items... such as washing machines / dishwashers etc.. same reason as above..

IT / AV equipment... many of these have some sort of filtering which strips the AC of any distortion and passes it to earth as a few mA of leakage.. it all adds up..

anything with a heating element.. immersion heater, cooker etc..


also, what method of "disconnection" did you use whilst on holiday?

unlpugging everything still leaves things like lights and such attatched, as well as outdoor cabling / sockets etc..

switching off the breaker doesn't isolate the neutrals so any circuit could be at fault when the fridge kicked in and drew more than about 5A....

 

[ROMSTER]

Thanks for response.

Question : is it actually feasible to locate the cause of a problem like this - and if so what should I be asking an electrician to see if they are competent? Especially since the installation was tested by someone who should know better soon after it was wired up.

To clarify on points:

1) the tripping happens randomly - but can anyone confirm will it only be caused by circuits that are protected by the RCCB - this will narrow things down a bit to those circuits [I'll try turning off outdoor lights etc as per posting]

2) there are actually 2 13a socket circuits downstairs (1 for kitchen and 1 for everything else). We can force a trip by plugging the iron into either one [before anyone states the obvious its a brand new iron as I thought the old one was causing the problem - the new one causes the trip as well]. This suggests the problem is not limited to a particular socket or circuit on these 13a circuits - rather the iron tips the RCCB over the edge

If the RCCB is only impacted by circuits wired through it I may be able to disconnect appliances etc and use the iron to blast the system and see if I can make it trip - that will allow me to isolate a circuit and maybe an appliance

 

[sparkyspike]

Did you receive an installation certificate when the new RCCB was installed? If so, it's unlikely to be a fault with the RCCB itself as it would have been tested up to 15mA and trip times would have been measured.

It's usually the case that small earth leaks, which Col Jack has listed, are all contributing to a total of more than 15mA which is tripping the device. Once you are certain that all appliances are disconnected (you need to disconnect the neutrals as well as the live conductors) then you can query the operation of the RCCB. It's hardly ever the RCCB, although they can vary in sensitivity.

You can ascertain which circuit the earth faults are on, by, with the MCBs open, removing the neutrals from the CU.

You can test using your iron, but this will only give you an idea of where the leak is. It may be that by seperating the circuits, you can't get the RCCB to trip at all. This is where you need an electrician to a) test the correct operation of the RCCB and b) test the circuits and appliances for earth faults.

 

[ColJack]

simply turning the lights off will not be enough unless they are on double pole switches..

generally yes, it should be only those circuits protected by the RCCB, however, if someone has put the neutral from a circuit in the wrong hole then it should be tripping as soon as you plug something in..


your first port of call should be to unplug everything and then try the iron... if it still trips, this will then count out all the appliances with plugs..
if it doesn't trip, then plug stuff back in one by one untill it does.. then remove and insert different things in different order to make sure it's not just cumulative..

if it does trip then the next bit is to call in the sparky.. he should first visually check the wiring in the CU to make sure there are no stray neutrals in the wrong holes and such..
next is to test the RCCB to make sure that it's not faulty..

that proven he should then start disconnecting the circuits one by one from live and neutral and repeating your "forced trip" to see when it stops it tripping..

this will narrow down the circuit causing the problem..

finding it once narrowed down, well that's a trade secret..

 

[ROMSTER]

Thanks all - investigation time will now begin!