RCD won't reset - weird symptoms

[steve_s46]

I've been having problems with the RCD tripping a couple of times over the last week or so, but each time I reset it it was ok for a couple of days. Now whenever i try to switch it back on, it just springs back.

There are 4 circuits on the RCD - 2 socket circuits, oven and water heater. With either of the socket circuit MCBs switched on, the RCD springs back straight away. With just the oven MCB on, it works fine until I switch the oven heater on and draw any current, then it trips straight away. Also with all the MCBs switched off, the RCD will stay on for maybe 10 minutes but will then trip - even though there should be no current flow(?) Could this be a fault somewhere within the CU itself..... Any ideas what to look for/check?

cheers, Steve

 

[Adam_151]

Neutral -> Earth fault, switch the mcbs off, disconnect the neutrals, reset the rcd, it should stay on, then add circuits in one at a time (being careful not to make split rings in the process), and test it untill you are happy that it doesn't trip, when you find the one at fault, disconnect that, put all the others back, check it still works, then investigate the circuit you have found to be at fault.

Obviously when you have your hands in the CU, you should have the main isolator switched off

 

[Qedelec]

not a good idea to have the oven or the water heater on the RCD side. Earth leakage is a problem with cooking appliances.

 

[steve_s46]

Thanks for the suggestions - will try disconnecting the neutrals. I think whoever installed it put the over and water heater on the RCD because in the CU the side marked "not protected by rcd" is full, but maybe i could swap the oven to non rcd and make something like the upstairs sockets rcd protected.

 

[Qedelec]

A good idea, you never know when you'll need to plug the mower into the upstairs ring

 

[Adam_151]

A good idea, you never know when you'll need to plug the mower into the upstairs ring

You never know, he might be working on the downstairs ring and have it turned off, and another family member decides to mow the lawn and extension cable gets chucked out the upstairs window...

Or he might put rope light on his guttering at christmas...

 

[tim00]

Adam, what is a "split-ring"?

 

[Adam_151]

nm, sorry wrong thread

 

[securespark]

It could be a dodgy RCD.

If you can get hold of an RCD tester, this will tell you the level of fault current at which it is tripping. If it is tripping out at (say) 16mA, you know it's faulty.

 

[steve_s46]

Checked RCD and it tripped just below 20mA. Replaced RCD and moved oven to non RCD side. Also found upstairs sockets were on the RCD and it looks like someone has borrowed a neutral from somewhere which allowed current to flow to the non RCD side - hence it tripped whenever any load was placed on it. Moved the upstairs ring to non RCD side and all seems to be working fine. Thanks for the advice!