I'm involved in specifying the supply for an application that needs a fused connection unit with a
key-operated switch.
This will be supplying a device embedded in a wall, with cabling channelled from the FCU to the
device. Current draw would be 3A, probably a 5A fuse in the FCU.

I was looking at 'making' one using parts from MK's GridPlus range -
a 2-unit faceplate K3632 (RS 341-4042),

with a 'secret key' 20A DP switch K4917 (RS 341-3982)
http://docs-europe.electrocomponents...6b8002c8a0.pdf

and a fuseholder K4890 (RS 341-4008)
http://docs-europe.electrocomponents...6b8002c890.pdf

However the electrical contractor on-site claims they can't do this as it will be connecting to a
30A ringmain and the switch is only rated at 20A.

The fuse would located right next to the switch on the faceplate, and be connected directly to the
output of the switch, and the switch will only be switching 5A (13A if the wrong fuse gets fitted).
The switch has a cable capacity of 2x2.5mmsq or 2x4mmsq.

Is their guy right? If not, can anyone suggest how to correct him without causing offence ( e.g.
quoting a reg...).
This will be installed in a school if that makes a difference ( hence the need for the key
operation).

or does anyone know of a key-operated FCU that will fit a single socket back-box?