Need quick help with IT room

[David.]

morning chaps,

got a room that is now going to be used as a computer room. Approx 8-10 computer couple printers and maybe odds and ends.

Going to run dado trunking of which totals approx run of 11 meters.

Im after a bit advice my idea will be suitable Im thinking of....

running a 20A MCB submain in 2.5mm T&E from 3P+N DB to a new board in the computer room.
into 100A main switch
then have 2x 16A 30mA RCBO Type C
2.5mm T&E from each RCBO feeding 5 double sockets each with "Computer Socket" stuck on
run a seperate earth to ensure high integrity

im hoping this should minimise nuisance tripping and provide a local means to reset RCBO should it trip. The submain cable is going to be fed through the ceiling.

My background has been industrial/machine/panel wiring short spell house bashing so commercial setups i've never been in?

thank you

 

[Spa Key]

Are you sure a 20A MCB will be enough? 10 computers will use nearly 3kW, add on top of that monitors, printers etc, while not using much energy might be enough to eventually trip it.

As for using RCBOs, what's the thinking behind type C breakers? That refers to the overload. Computers typically leak ~3mA to earth. 30mA RCBOs never trip at bang on 30mA, it's usually around the 20mA mark, sometimes less. Can you not put the computers on an MCB and lable the outlets for computer use only?

 

[David.]

My general knowledge of computers was approx 300W per unit including monitor?? there will be 1 maybe 2 printers at most
3000/230V = 13A so i thought 20A MCB would be enough even with a couple of printers I cant see it been much more?

I was going to use type C for possible in rush currents incase all machines are started at same time. Im aware computers leak to earth and that was why I had split over the 2 RCBO's. It might be cutting it fine with regards to around the 20mA leakage but I cant see it been viable having each computer on a seperate RCBO

With regards to MCB and labelling this is a possible idea however I feel that a RCD protection is a better option

 

[GStueyXR]

Better to limit to 3 computer terminals per 30mA RCD.. And if there is a server, put it on it's own circuit.

 

[Spa Key]

My general knowledge of computers was approx 300W per unit including monitor?? there will be 1 maybe 2 printers at most
3000/230V = 13A so i thought 20A MCB would be enough even with a couple of printers I cant see it been much more?

I was going to use type C for possible in rush currents incase all machines are started at same time. Im aware computers leak to earth and that was why I had split over the 2 RCBO's. It might be cutting it fine with regards to around the 20mA leakage but I cant see it been viable having each computer on a seperate RCBO

With regards to MCB and labelling this is a possible idea however I feel that a RCD protection is a better option

It depends on the size of the machines, but personally I wouldn't want to run the risk of installting 2.5 T+E on a 20A breaker then having to go back and replace with 4/6mm and a 32A breaker. As this is commercial what's the likelihood of other devices being put in there over time?

16A B curve breakers won't even think about tripping with 5 computers starting up. Haven't got my regs with me, but in situations like this I don't think RCD protection would be neccessary.

 

[David.]

Better to limit to 3 computer terminals per 30mA RCD.. And if there is a server, put it on it's own circuit.

good advice.

Unsure about server as this has not been mentioned but I will keep this in mind

Can i just clarify with regards to the labelling method. I could simply run an ordinary 32A ring main, inc high intergrity earth, label each socket as COMPUTER ONLY and this would suffice?

TY.

 

[mogga]

if your using dado why are you using RCBOs? have you thought about UPSing it?

as for submain Id be using 4mm possibly 6mm to allow for expansion anyways

 

[David.]

ok,

im having a re-think and wonder would a 32A 2.5mm ring main from DB into dado trunking with sockets marked "computer use only" be a better solution?

pls and thanks

 

[GStueyXR]

If running a 32A ring, why even bother labeling ?

Deffo find out if there is a file/services server though, and run it's own radial circuit and label that socket.

 

[JUD]

have you thought about UPSing it?

I would have thought that was the customers decision.

 

[ian.settle1]

My general knowledge of computers was approx 300W per unit including monitor?? there will be 1 maybe 2 printers at most
3000/230V = 13A so i thought 20A MCB would be enough even with a couple of printers I cant see it been much more?

I was going to use type C for possible in rush currents incase all machines are started at same time. Im aware computers leak to earth and that was why I had split over the 2 RCBO's. It might be cutting it fine with regards to around the 20mA leakage but I cant see it been viable having each computer on a seperate RCBO

With regards to MCB and labelling this is a possible idea however I feel that a RCD protection is a better option

Most PSUs in a PC base unit are now 350w with the monitor totally seperate, the days off where you connected the monitor into the back of the PC are long gone.

The 19" flat screen monitors we have in are place are rated at 1.5A which is another 345w so you are looking at approx 700w per computer station

 

[JUD]

Most PSUs in a PC base unit are now 350w

That's not to say that it will be using this much. It would depend on what is installed on the motherboard etc. and what the computer is being used for. For everyday office tasks the power usage should be minimal.

I have a 500W PSU installed on my PC and it very rarely uses more than around 150W.

Also 345W for a 19" monitor seems a bit excessive. My 22" only uses 40W.

 

[GStueyXR]

I have a 1000W PSU and use every last drop of available power to run Xfire and overclock the hell out of my CPU... But I am an exception, you see, I am a complete geek. Wouldnt mind, use the computer almost exclusively for office and internet stuff LOL.

 

[benji]

you don,t state the distance from the 3phase db to your new cons.unit,personally i would,nt use less than 10/16mm plus additional earth.

yours benji

 

[JUD]

I have a 1000W PSU and use every last drop of available power to run Xfire and overclock the hell out of my CPU... But I am an exception, you see, I am a complete geek. Wouldnt mind, use the computer almost exclusively for office and internet stuff LOL.

I suppose if the office is full of people like yourself all playing Crisis online instead of working then they may need a new three-phase supply just for the PCs

 

[David.]

you don,t state the distance from the 3phase db to your new cons.unit,personally i would,nt use less than 10/16mm plus additional earth.

yours benji

approx 5 meters at the most.

 

[davelerave]

the 20amp sub-main will deffo be undersized


i'd be looking more at type A rcd protection for the circuits than the C type protection for inrush

i'd say' B' is ok as they won't be switched on simultaneously

 

[David.]

the 20amp sub-main will deffo be undersized

yeah i agree now that its been mentioned computers use a lot more power than what i originally thought. I had based the 20A on 10 machines running 300W each.

TBH i think im going to just run a 32A ring main. Its all in trunking anyway and it saves fussing about

However im still wishing to learn and understand so if I were to run a submain in 6mm fed by a 32A MCB to a small CU with 3x 16A RCBO type B would that have been OK??

 

[cornburn]

yeah i agree now that its been mentioned computers use a lot more power than what i originally thought. I had based the 20A on 10 machines running 300W each.

TBH i think im going to just run a 32A ring main. Its all in trunking anyway and it saves fussing about

However im still wishing to learn and understand so if I were to run a submain in 6mm fed by a 32A MCB to a small CU with 3x 16A RCBO type B would that have been OK??

Your 3x16A would have been radials I take it so would probably have been best running another earth back in a ring so you have high integrity earthing. Bugger saying that I've just remembered last night I put both ends of a high integrity ring under the same screw at the CU. Ah well, I'll just have to put high integrity(ish) earth on the cert. Crapbags