rcd tripping randomly

[hogster]

I know only the basics about electrics so excuse my ignorance, for some reason the RCD on our consumer unit has started tripping, all kinds of odd times of the day and night,we've had nothing done to the house electrics recently except changed a couple of bulbs,rang a sparky friend of mine he said, in his experience, fridges and immersions were the main culprit as they tend to turn on and off randomly to maintain temp.
He said I need to plug/unplug stuff to isolate the cause and go from there,but because it's so random that could take forever whilst I unplug individual appliances and wait for something to happen.
The thing is, we can go for days and it doesn't happen,using all appliances in the house as usual,then for no apparent reason(like tonight)just sitting watching the box, the lights started to flicker and bang(not literally), everything went off(sockets)RCD tripped,it resets everytime, no problem, without turning off or unplugging anything ...very annoying, any ideas chaps?

 

[Lectrician]

Lights start to flicker but do not go off with the RCD?

 

[hogster]

That's right, when the RCD trips it only knocks out all the sockets...lights still work ok.
I thought the RCD should protect all the electrics,but it seems not in our case.
What causes RCDs to trip I know it's some kind of earth problem,can it be as simple as a dodgily wired up plug?
In my old house everytime a bulb blew it tripped the MCB,can a dodgy bulb cause the RCD to trip?

 

[Spark123]

Can you get your sparky friend to come and check all the terminals in your consumer unit are tight? (There are live wires in your CU hence use someone who knows what they are doing.)
Do any of your neighbours have a similar problem with the lights flickering?

 

[viewer]

Suspect that a wire has been "pulled" when you changed the bulbs. As the temperature changes the wire moves a fraction and gives short (either L to N r E, or, N to E). You need to check each rose / pendant in turn, but check the one with the last bulb change first.
HTH
V

 

[mikeyd]

Suspect that a wire has been "pulled" when you changed the bulbs. As the temperature changes the wire moves a fraction and gives short (either L to N r E, or, N to E). You need to check each rose / pendant in turn, but check the one with the last bulb change first.
HTH
V

The OP stated his lights stay on when the RCD trips, so the fault is not likely to be on the light circuit.

Hogster: Can you list which other circuits apart from your sockets are protected by the RCD (Cooker, immersion etc)

 

[JohnD]

I think you mean that when the RCD trips, the sockets go off but the lights still work, is that right? that is the usual arrangement in the UK with a split-load consumer unit which is very common now.

When a light bulb fails, it often creates a very short term high current which will trip an MCB (which detects overcurrent and short circuit faults) but does not cause an earth leakage, which is what an RCD detects.

An RCD trips when there is an earth leakage, this is most often from a watery appliance such as an immersion heater, kettle, dishwasher, washing machine or steam iron. It can also be from a central heating boiler or circulating pump, when there is a slight water leak that reaches an electrical part. Also an outdoor socket or light that has got rainwater inside it.

If it is not a watery fault, it can be a heating element, such as an electric oven, especially as they age.

If none of these, it can be a wiring fault; such as nail into wall touching wires; damaged flex; mice or puppy gnawing cables; heavy appliance put down on its own cable.

Easiest thing, as your friend suggested, it to try isolating the most suspect appliances, preferably by pulling their plugs out rather than just switching off. the cooker and boiler ought to have dual-pole switches provided they are reasonably modern, so you can switch those off at the wall.

The immersion heater ought not to be on the RCD, but if it is, it should have a DP switch as well.

The good news is that you do not have to try unplugging one appliance a day for the next 20 days!

Unplug half of then for one day; see if that cures the problem. unplug the other half the next day, see if that cures it. If so, you can then proceed to narrow it down by dividing in half the bunch of appliances that appears to include the faulty one. But, as I say, it is most likely a watery appliance, so start with all of them. If you have any appliances with loose or frayed flex or damaged plugs, stop using them.

Give this a try for few days and let us know what happens.

p.s. regrettably, it sometimes happens that a fault on a non-RCD protected circuit causes the RCD to trip. This very annoying and makes the fault difficult to find, but it is not usually the case. I bet you 5p you find the fault by unplugging appliances and looking for damaged cables

p.p.s. the flickering lights suggest cable damage. Have a look round for anything damaged or badly connected. this includes heat damage, for example if you have an electric shower which has a very heavy load and can overheat the switch.

 

[Lectrician]

Dodgy neutral in supply to property. Are you fed from overhead?

Lights flickering (which are not on the RCD side) followed by RCD tripping is a big clue.

Many RCD's will trip with a loss or partial loss of the neutral. You will also find that fluctuating voltage will cause RCD's to trip.

 

[RF Lighting]

Dodgy neutral in supply to property. Are you fed from overhead?

Lights flickering (which are not on the RCD side) followed by RCD tripping is a big clue.

Many RCD's will trip with a loss or partial loss of the neutral. You will also find that fluctuating voltage will cause RCD's to trip.

I've seen this a couple of times. Nightmate to track down too

I even took a particually poor quality video of a loose neutral in the supply head to this property. Watch the RCD

 

[hogster]

Yes we are fed from overhead if that's any help,by the way thanks JohnD for the detailed help....thank you EVERYONE certainly given me some pointers that I can pass on to my sparky buddy,when I can get hold of him!
Lectrician, when you say "dodgy neutral in supply to property" would that be my end(CU) or the leccy board?

 

[Lectrician]

As you have flicking lights I would report this to the DNO as a first course of action.

 

[Lectrician]

They should have recorded it as a Zdb, not a Ze.......but this is a little anal.

 

[hogster]

Sorry Lectrician.....DNO? Zdb? Ze???

 

[hogster]

Ah, got the DNO,googled it.....Distribution Network Operator

 

[hogster]

Also found the Zdb and Ze thing but that made my head hurt,got some bloke coming round from the DNO to check all their kit out,see what he has to say.