rcd triping when operating landing switch

[casamena]

evening all, i have recently installed a new dual rcd consumer unit at my house. the old cu had cartridge fuses, one was a 5 amp for lighting upstairs and down stairs one 30 amp for sockets and one for cooker.
i separated the 2 feeds for the lighting and connected on opposing rcd sides. one which for downstairs lighting and the other for upstairs.
my problem is that the landing light operating via a 2 way switch bottom and top of stairs will trip the rcd when switched. even if the mcb on that circuit is off it will trip, and when i use the top switch both rcds will trip.
stupidly i may of nipped one of the cables as i used a cable as a draw to bring in the new kitchen ring that i wanted concealed behind the wall instead of in trunking down to cu. or could it be that the 2 lighting cables should not of been separated. as you'll see on a previous post about a single black becoming live when switched this is wired in singles.
any suggestions welcomed.

 

[electronicsuk]

You have a borrowed neutral on the landing light.

The information you need is here.

I wont even get started on Part P and the like, as clearly the work is already done...

 

[casamena]

You have a borrowed neutral on the landing light.

The information you need is here.

I wont even get started on Part P and the like, as clearly the work is already done...

i suggested if this was a borrowed neutral apparently its a It is a back-feeding open circuit neutral as suggested by RF lighting. allthough this was on another part of the lighting circuit and not on the 2 way.

as regards to part p i informed my labc and contacted my supplier who fitted an isolator between tails and my cu.

 

[sparkwright]

You have a borrowed neutral on the landing light.

The information you need is here.

I wont even get started on Part P and the like, as clearly the work is already done...

i suggested if this was a borrowed neutral apparently its a It is a back-feeding open circuit neutral as suggested by RF lighting. allthough this was on another part of the lighting circuit and not on the 2 way.

as regards to part p i informed my labc and contacted my supplier who fitted an isolator between tails and my cu.

That was a previous post about another room and may not necessarily be related.

It sounds like you have a borrowed/shared neutral between the two lighting circuits. This may anywhere within the house.

Or you have a neutral in the wrong neutral bar at the cu.

 

[sparkwright]

It may be very difficult to sort out the neutrals, depending on how it's been wired so you may have to put the two lighting circuits on the same rcd to prevent the tripping.

 

[1john]

basically for you, the live feed to the landing light has be introduced at the ground floor switch from the downstairs circuit but the neutral to the light has been taken from the upstairs circuit.

there are multiple ways around this which involve installing new cables.

trace the neutral on the landing light back to the light it is taken from, disconect and remove and install a new cable from a rose downstairs and take the cable upto the landing light.

or

remove the link in the ground floor switch (assumed it is a 2 gang) if not then trace the feed back to the source it comes from and disconnect and remove it, then run a live cable from an upstairs rose down to the round floor switch.

 

[ban-all-sheds]

as regards to part p i informed my labc.

When you did that, what did you tell them would be the way you would comply with Part P?

What tests did you, or they, carry out before you energised the new CU?