Quick one…

 

Main board in property is all RCBO and radial 40A to a secondary board in the internal garage. 
 

Secondary board has RCBs feeding socket, lights etc in the garage plus a dedicated 16A feeding an external power to a shed/greenhouse 15m away via 3 core 2.5mm SWA terminated at an adaptable box. 
 

Initially the shed was only having a double socket internally however been asked to also put lights in there. 
 

Do I… spur off the power and use a fused spur to power the lights, or just put a small CU in the shed and give everything it’s own circuit…? 
 

Or is it worth not exporting the earth, protecting the armouring at the garage end and then installing a rod at the shed with an RCD at that point ..?

 

@ProDave any thoughts ..??

 

I would just use a switched fused connection unit with a 3A fuse as the light switch.

 

The earthing is a different discussion. Many don't like exporting a PME earth, but my take usually is use the PME earth and supplement it with another earth rod at the shed, adding to the "multiple" earths.

 

I assume it already has rcd protection, either an rcbo in the main house cu, or an rcd in the garage cu?

Thanks @ProDave

 

Initial feed to garage is RCBO in main CU

 

Just considering the earth trip risk and how to potentially stop the main board tripping the RCBO and not just tripping locally in the shed. 
 

 

If cable routing allows swap rcbo in main CU for MCB and then have an rcd or rcbo CU in garage so at least a trip would be more local than having to go back to the house to reset it.

 

All my outbuildings only have local RCD's in their own CU's

Did wonder if a CU in the shed with RCD and both earth rod and exported earth may respond quicker to a trip. May do it as belt and braces.