Fault Finding Help Please, Random RCD Tripping.

[daerve]

Hi all, new to the forum and hoping to garner some of your expert knowledge.

I live in a small 2 bed house and the main RCD on the consumer unit keeps tripping randomly.

There are 6 separate circuits and by elimination I've ruled out the lot except for the sockets (all on one ring).

Now I'm struggling to replicate or locate the fault, sometimes it goes off after a couple of minutes, sometimes an hour. I've tried unplugging everything and though I now have managed to keep it on for a couple of hours by removing an extension lead I'm not convinced it's the cause because the extension only has a lamp, macbook charger and iphone charger connected. It started this morning not long after we got up.

In addition I'm getting dodgy readings between live and neutral on the burglar alarm (2000 ohms) but this is on the lighting circuit and it still tripped when I removed the fuse for the alarm and had the lighting circuit turned off.

I'm stumped and though I have a decent multimeter (fluke) and used to work as a linesman I'm struggling on how and what to test.

Any advice or pointers would be welcomed with tears of joy because I'm well out of my depth here. Once the fault is located I can fix it a doodle but I just need to find it first.

 

[valleybilly]

Without an MFT to test the RCD your anwsers could be unlimited

 

[daerve]

Without an MFT to test the RCD your anwsers could be unlimited

What's an MFT?

 

[baazab]

removing the fuse is not going to solve the fault,sound like N/E FAULT in the circuit ,which circuit?

 

[daerve]

removing the fuse is not going to solve the fault,sound like N/E FAULT in the circuit ,which circuit?

The burglar alarm is on the upstairs lighting circuit but the main RCD still tripped when this was isolated via it's individual RCD which led me to believe it wasn't that circuit at fault.

 

[DNS1]

What's an MFT?

Multi-function tester.

 

[SPARTYKUS]

I understand what you are saying, but I suspect your fault will remain until you employ the services of a competent domestic electrician.

Update: where are you in WM? Someone might be able to help?

 

[Octopus]

Mice, rats, cable partly burnt by downlight, cable burnt by central heating pipes, leaky roof, leaky radiator, stray nail into cable, faulty light fitting, faulty appliance......

could be pretty much anything.

 

[mickys86]

The burglar alarm is on the upstairs lighting circuit but the main RCD still tripped when this was isolated via it's individual RCD which led me to believe it wasn't that circuit at fault.

The rcd is between neutral and earth. Isolating the mcb would make no difference, it could still trip

 

[ackbarthestar]

I'd start by disconnecting the Dish washer, Washing Machine and anything else that is hard wired.

I'll do you a deal, since you are a linesman, you might like to upgrade my incoming neutral conductor since it looks thrashed....

 

[ExArmy]

how about disconnecting one circuit at a time from the CU and leave for a few days each time? you will have to flick the MCB off and disconnect the associated neutrals. it will take some time but without an MFT the only way to go

 

[KevinS]

Sorry to say it, but the easiest and quickest way to sort it is to get a spark in, might only take him 5 mins.
Best bet, is, unplug everything u r not using, and I mean everything, and I mean physically remove the plug, see if the problem goes away, if it then still goes off, unplug everything, make sure no neons, switches etc are on
if u still have a problem it's on the circuit, u need a spark, if it goes away, plug one thing in at a time till u find the culprit

 

[ohmeelectrical]

The rcd is between neutral and earth. Isolating the mcb would make no difference, it could still trip

An RCD that complies to BS61008 does not have a connection to earth, it has connections to live and neutral. Some manufacturers put earth connections on RCBOs but they are not mandatory if you check BS61009. An RCD detects an imbalance in the current between live and neutral.
There is no relationship between neutral and earth on an rcd and they were devised to overcome the problems of earth faults and ELCBs.
If I am wrong please tell.

 

[Knobhead]

Your a bit late!

 

[ohmeelectrical]

Your a bit late!

Yes I know, I was trolling for inspiration on a really weird RCD fault and found this thread. Wishful thinking as the property has old and overloaded wiring, wires touching pipes all over the place, leaks in a flat roof, ancient appliances and scatty tenants from Goa.
I think prayer is my only hope on this one.