On 05/12/2012 21:13, Stephen H wrote:
Hi all,

I'm building a computer server farm, network switch rack and
TV/Sat/Radio headend in my loft. All of these gadgets need 240 volt
power via 13amp plugs.

This means lots and lots of double sockets. :-)

I'm planning on putting in a 32A RCBO in the CU to power all this kit in
the loft via suitable wiring.

The reason for a separate RCBO is to ensure high power availability so
that faults elsewhere in the house do not kill power and hence cause
data corruption in the computer servers.

Now, I have acquired some 2nd hand bench power strips that are basically
white plastic trunking with double sockets inserted. They are wired in a
ring main fashion within the trunking and had a RCBO in at one end.

See https://www.dropbox.com/s/562yp1r27v...Close%20up.JPG and

https://www.dropbox.com/s/kfcvrg71q9...mal%20view.JPG

I intend to modify all these by putting in as many double sockets as the
trunking allows which will be 10 double sockets over a length of 2 metres.

This entire assembly will then be fixed to the loft gable end wall and
then provide a fixed wired cable from this assembly back to the CU.

This will then power all my kit.

Now my questions:

Should I use a single run of 4mm2 cable run back to the 32A RCBO or
should I use 2.5mm2 T&E in a ring main fashion as per normal practice
for ring main sockets?

Will all this be compliant with wiring regs such as socket spacing &
density?

In the grand scheme of things, 32A seems a little excessive for the
expected load. While you may have lots of devices, the chances of them
drawing more than a few amp in total seems remote. Personally I would go
for 16A as more than adequate unless you really are running lots of
servers.

Given your loads are typically going to be IT kit and similar stuff with
lots of SMPSUs and mains input filters, you are potentially going to
have a circuit with normally high earth leakage currents. That suggests
you should be using high integrity earthing practices - which mandates a
ring connection on the CPC anyway. So a 2.5mm^2 ring circuit would
probably be the simplest way of doing this. Use sockets that have two
earth terminals, and wire using both.

The wiring regs are silent on socket spacing. The only density limit is
the floor area covered by each circuit - 100m^2 so not relevant in this
case.

--
Cheers,

John.

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