mcb/rcd tripping

[noeldownes]

I have a fairly modern consumer unit with mcb's and and an rcd. Tonight the rcd tripped and I have tracked the problem down to one particular circuit. Everything is fine when that mcb is switched off, but when it is switched on the rcd won't switch on at all. I unplugged every appliance that was on that circuit, but the problem is still there. No electrical work or DIY has been done recently.

Does this sound like a faulty circuit, and if so why should it suddenly occur out of the blue as it were

Thanks in advance for any help

 

[Steve]

What appliances are on that circuit? Any outdoors stuff you might have forgot? Outside light? fridge, freezer, boiler? kettle,washing machine, dishwasher, macerator, immersion, oven?

all the above are prone to developing leaks to earth, and could be things you forget when unplugging.

 

[sparkyspike]

If it's occurred out of the blue then it's often due to DIY (which you have eliminated), water (any junction boxes or anything at low level, or outside?), rodents, or mechanical damage (such as cables going to an outside light breaking down).

If you can't find it visually, then you'll need to use a meter to trace the fault. It's often possible to do this quite easily with a normal multimeter.

 

[noeldownes]

Spot on there - I hadn't thought of the immersion. Switched that of and the tripping stopped. I guess the first thing to do is replace the element, which looks positively ancient and a very likely suspect. Once again thanks guys

 

[Spark123]

It isn't considered good practice to put an immersion heater (in excess of 15L) on the same circuit as sockets owing to its load.