Conduit in garage

[snowdrift]

My garage has a double socket and a strip light. I was disappointed to see that the double socket was a spur off the socket in the bedroom. The strip light comes out of the socket with an FCU between the two.

Anyway, there is rigid conduit from the double socket to the FCU and then from the FCU to the garage roof. After that, the cable just runs along the underside of the roof to the light, and the switch cable runs without conduit along the roof before coming down the wall (in rigid conduit again) to the switch. Is there a reason they used conduit for the vertical situations, and just used bare cable for the rest? Seems a bit odd.

I had a proper sparky electrify my shed and he didn't use conduit anywhere...(except between the house and shed, obviously!)

And completely unrelated question - I read that if you are spurring off a socket, you have to use the same cable up to the FCU as was used in the ring main - but you can use narrower sized cable on the other side of the FCU. Why is that? I thought I'd ask before doing the inevitable outdoor floodlight installation myself...

 

[breezer]

because the fuse in the fcu protects the cable on the outgoing side, i.e the smaller cable

 

[DESL]

Anyway, there is rigid conduit from the double socket to the FCU and then from the FCU to the garage roof. After that, the cable just runs along the underside of the roof to the light, and the switch cable runs without conduit along the roof before coming down the wall (in rigid conduit again) to the switch. Is there a reason they used conduit for the vertical situations, and just used bare cable for the rest? Seems a bit odd.

Mechanical protection - the vertical runs are in a position that could exerience impact damage - the runs at roof height are less likely to as they are out of reach.

but you can use narrower sized cable on the other side of the FCU

That's the purpose of the FCU to fuse down accordingly to the rating of the smaller csa cable. Ring will protected by 32A fuse/mcb if you go down to say 1.5mm2 then 32A is too large to protect the cable against overload a 10A fuse would be used and for 1mm2 cable 5A fuse used.