Annoying RCD problem - please help!!

[sparklymarkly]

When I fitted our new consumer unit (before Part P!), I put all the ring circuits on the RCD side. This has been a source of annoyance for a while, as if a power tool in the gargage causes a trip, the whole house goes out incluuding computer etc. I have always meant to get around to sorting it...
Anyway, having just fitted a new shower unit (non electric but with built in small power pump fed via 3A fuse from spur on ring circuit), the RCD began to trip. As I've read on here many times about "watery things" causing tripping, I thought I would finally get around to amending the CU and taking the ring circuit off the RCD which I have just finished doing. Now I have a problem! The ring circuit works fine, but the RCD won't stay in at all. If I switch off the ring cct breaker, the RCD stays in. I cannot understand this. The neutrals are on the right side of the block (non-RCD) and the ringis fed from the non-RCD side of the CU. Has anyone got any suggestions please as I am tearing out what little hair I have left!! Thanks.

 

[Jim2287]

are you sure you moved the correct neutrals ? cant think of anything else


unless youve shared neutrals between circuits, 1 on RCD side and 1 on non-RCD side... which is really not allowed

 

[sparklymarkly]

As far as I can tell! There's a lot of cables in the CU and it's difficult to see by torchlight, but I'm pretty sure I moved the right neutrals. I tried a continuity tester between the neutrals I moved and the two lives and there was continuity, but I'm beginning to doubt myself now! I had a similar problem once before, but thatwas due to me putting the neutrals of an RCD protected circuit on the nonRCD side of the neutral bar. Someone on here pointed me in the right direction on that one (for which I am eternally grateful!!)

 

[JohnD]

I'm not sure I support your idea of moving the rings off the RCD because it trips! That's the idea!

If you get a lot of trips e.g. from the garage where you have a lot of faults, and you have a modern CU, you might consider putting the garage supply on an RCBO on the non-RCD size of the CU.

Certainly, if your shower is causing trips, that sounds like it has a prob, such as a water leak reaching the electrical parts, so I think you are making a mistake by wanting to take it off the RCD. Far better to find and rectify the fault.

 

[securespark]

Yeah, I agree. The whole point about a split-load board is that socket outlets likely to supply equipment used outdoors are protected by the 30mA RCD and other circuits (like lighting etc) are on the incomer.

This completely defies logic, and wired this way, the installation is no longer to current standard.

You need to find out what is the problem. Disconnect the outgoing leads/busbars from the RCD. Does it reset?

If so, you need to test it to see if it is tripping correctly. Do an autotest, then a ramp test. The first ensures the RCD's tripping characteristics are up to scratch. The second ensures that the RCD is tripping above 50% of the rated current. Below this is a definate fail. I like to see a minimum of 17/8mA.

If your RCD tests ok in isolation, then there is a problem with the circuit(s) attached to it.

Have you got lots of earth leakage? Even 2 x PC's and a freezer can trip a healthy RCD due to excessive levels of ELC. (NO, not Early Learning Centre!!)

Have you got a mix up with neutrals /busbars?

Is there a faulty appliance on the circuit? Be sure to unplug everything that has a plug, and switch off every DP switch.

You have to be thorough and logical, but you will find the fault....

 

[sparklymarkly]

Thanks for your comments guys.
I am a plank! I have now sorted the problem. Neutrals paired up incorrectly in CU (ie: one from one ring circuit & one from another in same terminal). This was fine when both circuits were on RCD side, but obviously not when I had moved one ring! Checked continuity on all 4 cables to ensure matched pairs and all sorted now and working fine!
The now nonRCD ring circuit supplies only bedrooms and my office. All the ground floor ring circuits, including garage are still protected by the RCD.
I may have also found the probable cause of the shower causing the original tripping - the bloody plumber hadn't tightened one half of the compression fitting which supplies it, resulting in a nice trickle of water down the inside of our newly built, plastered and painted wall. Doesn't seem to have come into contact with any electrics, but who knows?
Thanks for your assistance.