RCBO for Garage and Garden

[Johnnyboy1950]

I am in the process of upgrading my consumer unit from main RCD and MCBs for each circuit to main isolator and RCBOs for each circuit. Prime reason is to prevent whole house going off when a fault is detected in the garden, rats water etc.
Existing wiring has the ring main for the kitchen now with a dedicated RCBO and a spur from the ring out to the garden with an RCD and 2 MCBs. This better than before as a fault in the garden will only affect the kitchen. However I would rather just the garden supply trip for obvious reasons. I cant really run a new cable up the garden so would removing the garden RCD and 2 MCBs installing 2 RCBOs (lights and sockets) work? Would it be a matter of luck which RCBO tripped first?

 

[brianmoooore]

Would it be a matter of luck which RCBO tripped first?

Short answer is yes, and quite likely both would trip. Is it possible to get a new cable from the spur in the kitchen to the CU?

 

[Mike Johnson]

I found that isolating the earth to the garden circuits and putting in an earth rod helped the garden circuit to trip first on an earth fault, but don't think that would help on an overload, just haven't had one the test the theory, must get out my MFT and run it though everything and stop being lazy.