by ericmark »
Sun Jun 05, 2022 10:36 am
The RCD/RCBO/RCCD or what every other name it is given, was called an ELCB at one time, comes in many flavours, specially when looking at older units.
In the UK we have two types of supply, called TN and TT, with TN the supplier provides an earth, with TT the user has an earth rod, the use of plastic pipes for water and gas means the basic earth rod can not allow enough current to flow to cause a MCB to operate due to an earth fault. So back around the 1980's we started fitting ELCB's the early ones were voltage operated, and it was found they could all too easy be shorted out by accident so the ELCB-v was banned and the ELCB-c was used, this used an imbalance of current in and out to trigger them.
In the main we used 100 mA although one could get 300 mA and even on amp versions, these did trip the supply if there was an earth fault, but it was decided the human body can normally survive a 30 mA shock, so we started fitting 30 mA versions.
However the 30 mA trips far easier and it was soon realised having one trip for all was not going to work with most homes, first we went to using two with a split board, then the RCBO was produced, which is a MCB and RCD combined, so we used RCBO's on essential supplies and RCD's on the rest using what was called a high integrity board, and as the price of the RCBO's dropped we went to all RCBO boards, but with a TT supply they had to be double pole RCBO's.
So over the years the RCD protection has changed, and also the internals of the RCD, today we have types AC, A, F, and B where back 20 years ago we only had type S which was delayed and the no type S would often trip with spikes on the supply.
Today we fit a surge protection device (SPD) to stop these surges, and the modern RCD is not affected as much with spikes and surges, but in my old house where RCD's were fitted around 1992 resetting one could trip the other unless all MCB's switched off first, they tripped much easier than the new ones.
So a boiler which has a spark generator could trip the old type due to the spikes from the spark generator, old boilers had pilot lights. The diodes inside a three port valve can cause DC on the supply which can affect type AC RCD's today we tend to use type A.
You may still have one of the old voltage operated types. So there are so many reasons why yours can trip near impossible to work out remotely, and the earth - neutral fault can be very hard to find, as fault can be in toaster but when kettle is used the RCD trips.
With that last fault unplugging rather than just switching off can help, as switches often don't switch neutral, but often it needs either a clamp-on ammeter with a 0.001 amp resolution on the scale, or an insulation tester to locate faults, since both are expensive and need skill to use, the insulation tester uses 500 volt to test with, in the main not a DIY job, sorry to be bearer of bad news, but likely you need an electrician.
You can try posting pictures of the device which trips, we may be able to at least identify what it is, but seems likely you will need an electrician.
