DIYbanter - Electrical regs question

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Electrical regs question - key operated FCU

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?

Electrical regs question - key operated FCU

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

Electrical regs question - key operated FCU

On 29/05/2007 17:32, Mike Harrison wrote:

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.

Isn't that like saying e.g. on a cooker radial in 10mm^2 cable, you
can't continue the 10mm^2 from the oven connection unit to an FCU for
the hob, beacuse the FCU is switched at 13A while the circuit might be
fused at 40A?

Electrical regs question - key operated FCU

On Tue, 29 May 2007 16:32:05 GMT, Mike Harrison
mused:

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?

Contactum 3467 or 3469. Can't remember exactly what they are but they
are switched fused spurs with key operated switches.
--
Regards,
Stuart.

Electrical regs question - key operated FCU

In article ,
Owain writes:

One aspect is that if it needs a keyswitch then there's an argument that
the fuse carrier shouldn't be within reach of pupils either. So you
could use a FCU at high level with a keyswitch lower down, which might
keep everyone happy.

The gridswitch fuse carrier is retained by a screw,
so you need a screwdriver to take the fuse out.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Electrical regs question - key operated FCU