RCD Keeps Trippin!!!!

TPES · Sep 12, 2008

Hi All

Ive had a problem as the tittle says.

I have done a mains change from a very old Wylex board (4 way) to a 10 way hager board.
When i'd completed the change i had no problems at all.

8 hrs later i'd had a call from the customer saying all his electric had gone out!!

I got round to the customers house within 30mins.
The fault was as i had assumed the ring main was tripping the RCD. Its an old house with only 1 ring covering the whole house. Instantly as you flick up the breaker the rcd trips straight away.

The house has NOT been tested as of yet.
The customer had not switched any appliance on to cause the trip.
I had unpluged every appliance in the house and tried the RCD again..Nothing!
The board had been on and working fine for 8hrs no problem.
There was continuity through live, netural and earth.

To give the customer power again for tonight i had to put the ring onto the main switch side.

Im guessing there is some fault with the wiring of the ring main that only the RCD would pick up on and trip.

Is there any common cause for this? something i could check before removing every socket in the house?

Help appreciated.

sparkyork · Sep 12, 2008

firstly i think it should of been tested first for your --- is on the line otherwise!

could it be a dicky rcd? if not then has it been raining heavily on the job in question, theres more than likely alot of junction boxes here n there

id also drop the neautrals out and pop them back in to see which circuits are giving you problems

rich e roo

TPES · Sep 12, 2008

I agree, A test is needed ASAP. Which will be done in beginning of the week.
I’m just very curious to know the fault my self for future reference and if possible to prevent this happening again.

"there’s more than likely a lot of junction boxes here n there"

If this is the case and they are terminated correctly could this still be a cause for the fault?

Andy M · Sep 12, 2008

Why not call out an electrician?

TPES · Sep 12, 2008

Yes again your right, it does need testing. I know this.

tony.towa · Sep 13, 2008

From the fact that you cannot reset the RCD it would appear that you have a fault on the circuit (i know that sounds obvious). Being a new board the chances of the device being faulty is slight. When you get back there disconnect the lives, neutrals and earths for the circuit. Put the lives into one connector block, the neutrals into another and the earths into a third. Make sure no appliances are plugged in to any sockets. Check the resistance between live/neutral, live/earth and neutral/earth. Realistically you should show open circuit between them. If you do not get open circuit then, remove the cables from the blocks and seperate them, you can then start checking resistance from the sockets. If you are lucky enough to know the cable route then start at the half way point of the circuit, disconnect the socket and test the individual cable resistance. If you know the route then one cable will most probably show open circuit, the other will give you the resistance (short circuit), you then just keep halving the circuit and you will locate the fault. If you do not know the route then it is one socket at a time.
A word from someone who had a similar problem once. When you remove the socket covers check the state of the insulation on the conductors back to the outer covering. A slight nick in the neutral, touching the metal back box when the socket is in place will give you an earth fault when the socket is in place but not when the socket is removed.
The part that does not make sense to me is that the board was on for eight hours without a problem and the customer said they did not switch anything on, yet you had to unplug items from the sockets.
I know that at times we are all in a hurry but if testing had been done at the time of installation a fault of this nature is likely to have shown up and the state and effectiveness of the rcd would have been proved. Also, assuming that all your test results were ok differences when you test the defective circuit would have shown up.

By not testing at the time of installation you are unable to prove that the installation was correct when you left it and leave yourself wide open to "being responsible" for any fault that is caused by the customer between the time of installation and testing.

greekislandlover · Sep 13, 2008

One further note - when resetting the RCD, turn off all breakers. Turn on the rcd and press the test button. Reset the RCD and then turn on the breakers one by one, giving each circuit a few seconds before turning on the next.

Even if there isn't a fault on the circuit, with the entire house coming online all at once they will sometimes flip off. If there is a fault, at least you have some clues as to what circuit it's on if you turn on one by one.

marty1234 · Sep 13, 2008

when you say you unpluged everthing in the house remember things like tv amp in loft ,back gas boiler spur , have a good think if it possible everthing is unpluged before you start an other thought make sh central heating timer has nothing to do with this just in case the timer had come on 8h after you left and was on when you got back to look at this job .