RCD Tripping Randomly in Consumer Unit

Hi all,

Over the last 6 months I have had random trips of the RCD in my consumer unit. It is now going out sometimes twice a day or sometimes not for weeks at a time. It does not appear to be related ta any specific loop as I have left each one off for different lengths of time. Could it be a faulty RCD or can anyone suggest an easy way to approach finding the offending Cable, Appliance, Plug.... or is there a test tool that I can get to help with this?

Many thanks for any advice.
Gareth

The only test tool is an RCD tester - they cost a lot, though every Part P tester and a lot of other pro's will have one. A serviceable RCD trips when it detects an imbalance between the current flowing through the phase and neutral conductors - normally suggesting an earth leak. It is just possible you have a problem that is affecting 2 ccts eg, mechanical damage to 2 adjacent cables somewere in the house, so just switching one off will not isolate the fault.

I can only see 2 options open to you.
1. Replace the RCD to see if a new serviceable one exhibits the same problem (they do go faulty on occassions).
2. Get someone in to check the RCD.

If the existing RCD is OK, or a new one still trips, you will have to get someone in who can properly check the system (esp the insulation).

Keep in mind that if this RCD is tripping due to a fault then you must take action to sort it out as it is all there is between you and a potentially very dangerous situation.

Don't forget that an RCD will trip on an earth fault on either live or neutral so turning off the cb on a particular circuit will only isolate the phase part of the circuit. So if the intermittent fault is on a neutral leg the RCD will still trip (tricky little b*ggrs, eh?)

You need someone (as said above) with the right test gear to run ramp test on your RCD and perhaps carry out insulation resistance tests on the wiring.

Might be a mouse gnawing a cable under the floorboards; might be a water drip in the roof, under the floor or on an outside lamp (does it happen on wet days?)

There is also a chance that you have several small leakages (Washing machine, immersion heater; central heating pump; kettle; tea urn - usually the "watery" appliances) that add up to very near the tripping current. Tru actually pulling the plug out on any of these, or turning off their DP switch, instead of just flicking the MCB, as it could be a neutral/earth fault that the MCB will not isolate.

Intermittent faults are difficult to trace, you can have a look round, but I think you are going to need a pro.

(as Taylor says)

Yeah, three reasons:

1. Faulty RCD

2. Faulty Wiring

3. Faulty Appliance.

The trouble with your scenario is that the fault is intermittent, therefore very difficult to trace.

If it were a permanent fault, it would be much easier to trace.

As has been said you need to check your RCD: that it is tripping within the correct timeframe and not below 50% of its rated current. I usually smell a rat at much less than 18mA.

Sometimes, appliances leak small currents to earth. If these build up (ie more than one appliance is leaking or one appliance leaks more) to approaching the level where the RCD will trip, then it will.

If your RCD is OK (make sure the guy testing it checks it in isolation from the circuitry), then it is an appliance or wiring. As I aid earlier, if the fault were permanent, this would be easy to trace, as you could quickly eliminate appliances by disconnecting them, and using an IR tester, could identify which circuit were faulty.

The best places to start are things using water: Kettles, boilers, showers, WM's DW's, steam irons, imm htrs etc...

Lost one, won one

F in 'ell!! Same time 'n' all.....

Guy's thank you all very much. I am going to try a new RCD and if it continues call in the man who can (i.e expensive tester guy).

Will update you all with the final outcome.

Appreciate your time in responding, has helped me define my course of action.

Thanks,
Gareth