Shower on separate RCD - will it help

[xAlex]

I recently wired up some wall lights/ceiling lights. (Wall lights had never been connected since I moved in). Anyway, i think there is a bit of neutral-borrowing going on, but the wiring in the place is a nightmare (JB's under floorboards etc). I don't think I could sort it out without re-wiring everything.
Anyway - Everything was working fine until I turned the shower on. I know the shower circuit is fine (as I installed it). so....

I think the initial current draw from the 9.5Kw shower tipped the balance on the RCD. Can this happen???? normal operation of the shower causes lights to dim for half a second.

Secondly, if the shower is the straw that breaks the camels back, even if it is not the problem itself, might this be cured if I take a separate connection, pre-consumer unit, into a shower RCBO?, or would this still cause the same drop across the other circuits, so tripping the RCD in the CU?

Any advice appriciated.

Thanks
Alex

 

[electronicsuk]

Indeed, if you already have high earth leakage on your RCD'd circuits then the shower could be enough to cause it to trip. A separate RCD is one option, although if your CU will accept them, it would be easier to fit an RCBO in one of the non-RCD protected outgoing ways. It's notifiable work, though.

Also, if this has only started happening since the addition of the wall lights then it's worth looking elsewhere first. If you'd somehow borrowed an RCD protected neutral and an unprotected live, the RCD should trip as soon as you turn the wall lights on, assuming it's working properly. If the work was carried out properly then I can't imagine the addition of a couple of new lights would cause any notable increase in earth leakage.

 

[xAlex]

Indeed, if you already have high earth leakage on your RCD'd circuits then the shower could be enough to cause it to trip. A separate RCD is one option, although if your CU will accept them, it would be easier to fit an RCBO in one of the non-RCD protected outgoing ways. It's notifiable work, though.

Also, if this has only started happening since the addition of the wall lights then it's worth looking elsewhere first. If you'd somehow borrowed an RCD protected neutral and an unprotected live, the RCD should trip as soon as you turn the wall lights on, assuming it's working properly. If the work was carried out properly then I can't imagine the addition of a couple of new lights would cause any notable increase in earth leakage.

1. The RCBO on the non-protected side is a good Idea. There is a spare way but the busbar does not extend into it. Can i buy a new busbar?

2. All the lights were already there. We had a problem soon after we moved in, so I took the wall lights off. I only connected new lights back up yesterday - all was good until i turned on the shower this morning. Yesterday i belled-out the neutrals and got a positive from the RCD neutral bar and the non-RCD. Not knowing which other circuit on the RCD side was causing the problem, i connected the lights up to the RCD side, then (I figured), at least there should be a balance. Worked fine until the shower.

 

[electronicsuk]

1. The RCBO on the non-protected side is a good Idea. There is a spare way but the busbar does not extend into it. Can i buy a new busbar?

That really does depend on the brand and age of your CU.

2. All the lights were already there. We had a problem soon after we moved in, so I took the wall lights off. I only connected new lights back up yesterday - all was good until i turned on the shower this morning. Yesterday i belled-out the neutrals and got a positive from the RCD neutral bar and the non-RCD. Not knowing which other circuit on the RCD side was causing the problem, i connected the lights up to the RCD side, then (I figured), at least there should be a balance. Worked fine until the shower.

Was the RCD in the off position at the time? If not, you would expect to see continuity between both neutral bars, even with the main DP isolator open. If the RCD was indeed turned off then it seems that you may indeed have a borrowed or linked neutral somewhere in your installation, and you really should sort that out before looking elsewhere for faults or trying to skirt round the problem.

 

[xAlex]

...I did some more investigation tonight. With everything dead, I did a continuity check between the neutral at the switch and all the neutrals on the RCD side of the CU. 2 of them were positive. - upstairs ring and downstairs ring. So it seems that the lightswitch neutral is connected to 2 ring circuits. Nightmare.