A little advice would be appreciated.

[sjm]

Hi guys.

Does anyone have any knowledge/experience of computers and their power requirements.
I'm asking because I've been asked to move some existing supplies in order to supply a new computer suite in a primary school and am becoming concerned that there isn't enough current available.

The existing supplies consist of 3 x 20 amp radial circuits supplying 6 x double sockets each, with each socket supplying 1 x tower and 1 x monitor.
The computer tower has a rating plate giving power requirement of 3.15 amps and monitor needing 1.5 amps. So the exisiting supplies are underated.

So my question is do computers have a diversity or similar factor or do they always draw the maximum current as per the rating plate.

Any help would be greatly appreciated.
Many thanks in advance.

Steve.

 

[Big n Daft]

Make it into a ring...........

 

[madmac]

Also make sure you install high integrity circuit or sockets as per the reg. that I can't remember due to accumulative effects of earth leakage.

 

[mayfair]

4.65 A for a tower and monitor seems a bit high but if thats what it says!

 

[ruston]

Am I allowed to post a link to the IET to a thread that may be of help to you.

 

[sjm]

Many thanks guys for your speedy replies.

I was thinking I would stick to smaller radial circuits due to potential high earth leakage.
I will certainly be using high integrity earthing.
Yes 4.65 amps seems high to me as well, I might just phone the manufacturers and check.
Please ruston a link to IET thread would be most usefull.

Steve.

 

[SPARTYKUS]

Dare I say it, you may want to consider non Rcd protection if theres concern over them powering down?Depends what theyre for. It can be done though with some VERY careful planning and diligent interpretation of the regs.(*waits for the storm*).

 

[ruston]

Sent you a PM with it in case it is against the rules to link to another forum.

 

[alli]

Dare I say it, you may want to consider non Rcd protection if theres concern over them powering down?Depends what theyre for. It can be done though with some VERY careful planning and diligent interpretation of the regs.(*waits for the storm*).

Or if it can't be met, maybe RCBO's for each individual circuit?

 

[tlangdon12]

3.15A = 724 VA (@230V), so this will be the rating of the PSU, not what it will draw.

The PSU will be sized to cope with the maximum load the PC could draw, e.g. if it had two floppy disk drives, two DVD drives, two hard drives, a high-end graphics card, maximum memory, multiple USB drives, etc. Most PCs will typically draw less than half the load that their PSU is rated for (in steady-state). NOTE that these devices tend to have a high startup current that can require MCBs with different tripping characteritics (e.g. D curve rather than C) but I expect that this will not be an issue in your situation.

Similarly with the monitors, the load you reported is the rating of the PSU, not what it will draw in service.

You really need to test a subset of the PCs and monitors to see what they will draw in service, and arrive at a distribution network to suit - but allowing some headroom for growth.


In a school situation (esp. Primary School), I think RCDs/RCBOs are desirable, albeit this makes the installation much more expensive as the Earth Leakage current imposes additional constraints on the design. Moderns computer and Screen PSUs will leak as much a 3.5ma to earth, so it may not be possible to get more than 4 devices on a single 30ma RCD. This is a severe constraint, so if you are proposing to provide RCD protection, you really need to find out exactly how much earth leakage current each device will produce.

If you are proposing to provide RCD protection, you could do this with an RCD close to the PC/Screen with the supply to the RCD taken into the floor or ceiling void where little hands can't get at it. e.g. using an RCD protected PDU like this http://www.proteusswitchgear.co.uk/product_details.asp?product=4120
or a large number of RCBO supplies could be used but the supply to the PDU needs to be hard-wired where little fingers can access it.