Both rcd,s tripping with faulty light switch

[Topcat33]

I have consumer unit with 2 rcd circuits

Please see rather crude drawing. When I switch the second switch on it trips both rcd,s if there is no bulb in it doesn’t trip and also if I put a tester across the bulb holder that lights but doesn’t trip.

Why does it trip both circuits?

The neutral and earth for light 2 are from an unknown source buried in the wall

Also when I put a test lamp across l1 and com on switch 1 I get a light whether it’s on or off

Any help would be good

Thanks

 

[EFLImpudence]

No drawing - just copy and paste.

 

[EFLImpudence]

Has this just started to happen?

It sounds like a borrowed neutral or neutral in the wrong neutral bar.

 

[Topcat33]

All neutrals on the correct bars, looking at previous threads it looks like that neutral in the wall is probably the issue

 

[pete01]

Has it worked fine for years and it's only just started happening or has something been done/changed?

 

[Topcat33]

Yes it’s a new consumer unit installed in a house we bought by previous owners, my dad was an electrician many years ago so he checked the neutrals on the board

 

[SUNRAY]

Yes it’s a new consumer unit installed in a house we bought by previous owners, my dad was an electrician many years ago so he checked the neutrals on the board

I'll suggest checking again.

 

[Topcat33]

Would this happen if the neutral set in the wall is coming from a socket on the ring main which is on the other rcd?

 

[EFLImpudence]

Yes.