On Tue, 29 May 2007 16:32:05 GMT someone who may be Mike Harrison
wrote this:-


I'm involved in specifying the supply for an application that needs a fused connection unit with a
key-operated switch. [snip]

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.

The contractor is not particularly au-fait with electrical design
then. It is no different to fitting a spur in a kitchen which has a
20A switch at high level and a socket outlet at low level. The fuse
limits the current flowing through the switch to below that which
the switch is rated at. What it means is that overload and short
circuit protection are undertaken by different protective devices.

Neither is it different to fitting a switched socket outlet. Does
your contractor think that the switches of these are rated at
30/32A?

Why not connect the ring main to the fuse unit (which might be an
interesting task). Then the switch is on a fused spur and your
contractor should be happy.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54