RCD keeps tripping (apologies for on-topic post;-)

the sensible option however is to use a multimeter, as mentioned a while back

not now

non-RCD freezer feeds aren't permitted now, but of course dedicated RCBOed circuits are

RCBO. I don't think they have humour detectors though :)

common enough. The leading one ought to be S type so it doesn't trip when a downstream one does.

NT

I disagree. Multimeter testing is O(N) whereas a binary chop is O(logN).

The first thing to do is find and isolate the faulty circuit quickly. Then you can use a multimeter to close in on the actual fault.

Ah, do modern installations have a separate RCD (combined with the over-current MCB) for each circuit (downstairs ring main, upstairs ring main, lighting, cooker, shower etc)? I presume that's been driven partly by a reduction in price and in size (so they will fit in standard fuse/MCB slot).

Yes, There's probably something to be said for having a dedicated feed for the room where freezers are kept, to minimise the chance of a fault elsewhere killing important things like freezers. Or for having a neighbour who pops in each day and at least *tries* resetting the RCD :-)

Very funny!

I'm not sure how they were labelled. I think the one in the consumer unit gave rated parameters like trip current (30 mA), trip time (within so many milliseconds), but I don't remember anything on the ancient Bakelite one. What are the advantages of having two? Is it likely that the older one was fitted in the days of fuse wire, and then a new CU was fitted which happened to include its own RCD? Maybe the fact that either would trip at random suggests that the upstream one wasn't S type (delayed tripping).

I hadn't realised that an electric shock (of > 30 mA) for as little as 30 msec was enough to induce heart fibrillation. It's not a risk that I'd want to take these days. Having had a couple of mains shocks across the knuckle of one finger (so not hand-to-hand across the chest) I know the pain that it causes and how long it lasts after the shock, and having had a heart attack and cardiac arrest (not due to electric shock!) a few years ago, I'm probably more susceptible than I was. I may use the insulated probe of a test meter on live equipment, but I take care not to put my fingers anywhere near, and certainly not to touch earth with one hand while there's any chance of the other hand coming into contact with anything live.

FWIW We only have one RCD for the house. It was installed around 2004, when we had some other work done.

There are a number of MCBs for the different circuits in the house.

--snip--

Since it hasn't reoccurred since, then I think my assumption it was the washing machine is correct.

There isn't an easy way because nuisance tripping is often related to earth to neutral faults. Other common causes are lots of devices with mains filters such as computers, switched mode power supplies (sky boxes, PVR's etc) and mains powered water heaters or electric oven elements.

The problem with finding earth/neutral faults is that the fault and the cause of tripping may be on entirely different circuits. A common fault is nails through cables under floorboards bridging earth and neutral. That creates a small leakage current insufficient to trip the RCD but when something unrelated is switched on the perturbation is enough to trip the RCD even though the second device is perfectly serviceable.

Fault finding is firstly trying to unplug everything and disconnecting both live and neutral of wired devices followed by going through each circuit in the consumer unit disconnecting both live and neutral - live alone won't suffice. At least you have the RCD tripping consistently - when its only occurring occasionally the time taken to fault find can be considerable.

The other cause can of course be an over sensitive RCD. RCD's are not the most reliable of devices and over time will often start tripping at lower threshold currents. An electrician should have an RCD test device to determine the trip current of an RCD but as it will cost more than the cost of an RCD to get one out to test it may be worth simply replacing the RCD before spending hours disconnecting and reconnecting things. I'd be inclined to do that if nothing is found when simply unplugging everything/disconnecting hard wired devices. Don't forget to remove the incoming fuse before attacking the consumer unit RCD!

RCD's sometimes trip on current imbalance and that can occur on external circuits before your dwelling. A friend living in the country had an RCD tripped whenever the farm on the same feed as him switched on their milking machine. If the fault is new, has anything obvious changed outside the house?

sometimes that works, often not. A multimeter is by far the quickest & surest of the easy cheap diy ways.

NT

some do, most use a split CU with 2 RCDs

likely

I've had it from one firm gripping hand to the other firm gripping hand. Not much fun.

NT

He doesn't know what 'double pole' switching is, so is unlikely to possess test gear :-(

I thought you had to pay extra for that sort of 'service' , well according to the cards stuck in the local telephone kiosk.

I took it to mean he doesn't know which of his appliances had double-pole switching, on the basis that what you've suggested wasn't likely. BICBW!

It means using two men called Lech and Waclav to turn the appliance off. :-)

Sure. Multimeters are a fiver or so, as long as it has a high resistance range it'll do the job. They have lots of other uses and will pay back the cost several times.

Yes you can try unplugging things but that frequently fails to find the problem & wastes a ton of time.

NT

I've never seen killers for hire on kiosk cards - in Russia maybe?

NT

Correct.

Yep. The RCD hasn't tripped again and the washing machine has completely failed. Thanks to all who replied :-)

Last one we had was because a slug crawled into a socket. Unplugging wouldn't help.

Well, the remains looked a bit like a slug...

Andy