RCD issue baffling me Electrical Advice

RCD issue baffling me Discussion ThreadRCD issue baffling me Electrical Advice

I have a dual board consumer unit. Both sides have a RCD. The left hand side of the board has all the MCBs for all the 6 ring mains for the property. The right side of the board has the lighting and hob and cooker for the house.

Whenever a current is drawn from a socket the right side RCD trips, but not the left side. So my lights trip but sockets stay on. It happens on any of the 6 ring mains. And seems to be any appliance that draws a large current such as a hoover, kettle, immersion heater etc.

I do have a alarm system but I have totally isolated it by unwiring it front the spur it was connected to. Still the same issue.

I do also have under cabinet lights that are ran from a ring main... I have yet to investigate these.

The MCBs switched off were because they were just straight up tripping the right side RCD. Probably because they all had stuff like a fridge, boiler etc drawing current. The right hand side lighting circuit that is turned off also automatically trips the right RCD.

Electrician has tested each circuit and can't find a fault. The board has been wired correctly with no crossed over neutrals.

Anyone got any clue where to start some more fault finding? I am a ex Army Electrician, that was 17th ed trained... But that was about a decade ago but I know enough to be safe.

Cheers

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