outside light and socket??

[littlefellow]

Hi,

this is my firsty post. I wish to have fitted an external light and socket outside. the socket will be used for music/patio heater. I initially thought spurring off the ring main fitting a rcd then from this to outside socket and a seperate fcu for the external light so it could be powered independent to the socket. I then relised having 2 rcd on same circuit causes both to trip (i only wanted power outside to trip if failure occured).

So as my CU is RCD protected is it ok to spur off ring main with a fused switch for external socket and a second fused switch for the external light. This way i can switch off all power to outside when not needed so if for example i went on holiday a failure outside would prevent whole house tripping?

another one how come a rcd i have plugged into a socket inside does not cause the cu to trip when tested if that makes sense?

I hope all this makes sense and work will be carried out by qualified person. I just want to have an idea so to lower risk of having my pants pulled down over cost.

 

[flameport]

So as my CU is RCD protected is it ok to spur off ring main with a fused switch for external socket and a second fused switch for the external light.

Yes, they will need to be double pole switches, otherwise faults outside could still cause the RCD to trip.

another one how come a rcd i have plugged into a socket inside does not cause the cu to trip when tested if that makes sense?

The test button causes an imbalance by connecting a resistance across the RCD - typically between the neutral terminal before the RCD and the line terminal after it.
The RCD in your consumer unit won't trip as the test is all on one side of that RCD - it just appears as a normal load. To trip that, you need a connection before the CU, which a plug-in device cannot have.