Power to server & machine and headend room from CU....

[Stephen H]

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

and

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?

Regards,

Stephen.

[Dave Liquorice]

Do they have to be 13A plugs? Can you not use IEC connectors and a rack mounted PDU or even an IEC distribution strip?

I guess you have a number of wall warts though. When I do the server/comms/head end here there won't be any wall warts just a beefy 12v PSU and fused distribution to the various bits of kit. If I need a different DC voltage a small DC-DC converter will provide that.

I'm also sort of surprised that you need a 7kW+ supply, unless you have seriously powerful server farm. In which case I assume half of the 7kW is for the aircon to keep the loft cool in the winter. In summer you'll probably need all 7kW to keep the kit cool, lofts get damn hot in the summer... It might not be the best place to have electronics.

[harryagain]

The above is true. You really need to insulate the roof (sloping bits) if you are going to do this. The temperature up there could hit 40 degrees in Summer otherwise. You might consider the use of mulitgang sockets.

[John Rumm]

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.

[Brian Gaff]

Isn't this lot going to make the loft rather hot escpecially in the summer?

Brian

[Tim Watts]

A 20A radial might be easier to wire unless you really want a 32A ring

When Imperial College Dept of Computing had a student computer lab rebuild a few years back, the desks had laptop sockets run in a local ring (well, might have been a radial) one per row. Each desk had a local RCD for safety

• convenience (no remote RCD) and each desk row plugged into the underfloor power with a "commando" type plug. I *think* this was a 16A plug, so a 16A radial circuit.

Similar principle. No, there is no real limit to socket density as long as the protection is appropriate.

Conversely in the main computer room next door, each rack plugged in to a single 32A commando under the floor - again a dedicated radial circuit.