Electrical Wiring For Internet Cafe

tony_s

I was asked to bid for the Internet cafe which will be housing 40 computers
I have a question how to figure out the outlet circuits for those comps
the specification said each computer will be 450 w + 50 W for monitor.
if we use 20 amps circuits it would be how many computers/circuit ( the main panel is 200 Amps)

The drawing did not show any electrical wiring diagram but I just want to know the rough no. of outlets before I go farther and place the bid ( networking will be in another contract)

Thanks

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Magnettica

Gotta worry about harmonic currents with sensitive electronic equipment.

40 individual circuits (2-wire ckts) would be the way to go.

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Sparky Joe

You have 500 watts per computer and 20 amp circuits. These loads would be considered continuous(on for more than 3 hours) so now you have 16 amps available per circuit.

500watts/120volts=4.2amps per computer. Therefore you can put 3 on one circuit(12.6 amps per circuit). 14 circuits for the computers alone.

And like Mag said above, do not share neutrals. Each circuit should be run with its own neut. This is not for the computers, but to not overload a shared neutral or the transformer feeding the system. The computer power supply's have filters and don't care what you feed them so long as voltage is within tolerences.

Be sure to figure your pipe fill given the extra neutrals, but derating shouldn't be a factor.

By the way, where are you located? I haven't heard of an internet cafe since 1995. I thought everyone now has a laptop and only care about hot spots?

Bubbles

Pretty much agree with sparky although personally I would do 2 per circuit since you know they are going to plug other things in like scanners/printers and such that they can't foresee now. It always happens and since those things are continuous and run all damn day you can spend a few more bucks and put 2 per circuit but of course code wise your fine with sparkys as well.

Speedy Petey

All I can say about the bid is do not get very detailed in your bid. If you get the job then do so in the contract. This is a design build, do not design it for him so that the guys cousin can do the job for him later.

I would also say three per circuit.
This is a cafe. They will not be adding scanners, printers and other large peripherals at each place. Also, computers do not draw nearly full power full time. Not even close.

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mdshunk

I'm not sure what the budget is like, but you might want to look into just putting Wiremold 3000 around the room. You can run your data and power in that raceway (with a barrier) and add receptacles and circuits at your leisure at any point in the future.

Celtic

What is the total load on those 40 computers?

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747

I read about that stuff in a electrial magazine a while back. It looks like slick stuff. It is the way to go. But it also doesn't look cheap.

Ps. Internet cafe's are hot stuff outside of the U.S.

randomkiller

They are still popular in the UK and South Africa.

GregS

Hmm, maybe I should recalc my loads going into my server room. 2x 15A circuits run on 14.3. The main UPS shows about 900W. Hmm..

Sparky Joe

Is this server room in your house? Commercial circuits are 20 amps or more.

MinConst

I'm no sparky but was in charge of a computer factory and we would run allot of systems on 1 circuit. They were 20 amp circuits and we probably had 20-30 systems on each with no problems. As I remember we had one circuit per bench and each bench would hole 30 stations. All I mean to say is the figures don't add up like you would think.

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Paul
Minichillo's Construction
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Celtic

School me.

Show me how the figures don't add up like I think?

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Sparky Joe

That's what I was gonna say

Celtic

You still can ....you just can't have my pie or pastry

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Speedy Petey

Min, in commercial applications you have to prepare for worst case scenarios.
Like if every machine was running in defrag and the machine was pulling max watts.

This is also the reason it is a PIA to design build something like this as opposed to having engineered prints. You get apples to oranges.

We all know we can design a job like this, but you may bid it at three machines per circuit, and the next guy bids it with only two circuits for the 40 machines. Who wins the bid?

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MinConst

Like I said I'm no sparky just passing on a real world experience. I remember trying to figure this all out back then and didn't have the knowledge. The electricians did it when they built the building. But that is what we ended up with. It worked. Never popped a breaker unless we added more (much more). The server line had two circuits. They drew more at power up. We use to do what is called burn in on carts. We could fit maybe 30 machines on a cart and didn't trip a breaker until the third cart. All that was on the carts were computers and one monitor per cart.
You guys know the numbers and I didn't mean to say your wrong. Just an experience. However extreme.

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Paul
Minichillo's Construction
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mdshunk

There's not a doubt in my mind that what you're saying is true. From an electrician's standpoint, we're pretty much bound by what the dataplate on the equipment says. If it says 500 watts, then we wire for 500 watts per unit, without regard to what we might think the real draw might be. Electricians aren't really permitted to do otherwise, unless there is a design sealed by a PE that says we can.

GregS

Yes my house. Perhaps I shall run 2x 12.2 and change it over to 20A since I am adding more hardware in there soon.

tony_s

Thanks to all of you who replied,Actually it is somewhat like a Game center where kids play games through networks.

There will be 40 computers and each computer has 450 Watts ( the Drawing quoted from the computer power supply) plus 50 Watts for monitor
so it will be a total of 500 Watts The Drawing says:" The Contractor will be responsible for wiring & provide outlet for each computer " but there is no detail how to wire it

From The answers in this forum I would say I will go this way
(Please correct me if I am wrong.)

A) 1 circuit =20 Amps supply for 3 computers

500 w/120V = 4.17 Amp,4.17 Amps x 3 = 12.51 Amp

12.51 x 125 % =12.51 x 1.25 so the max amps for cable will be...16 Amps

B) 40 computers = 40/ 3 = 13.33 Say 14 circuits

c) I need to include the price to pay for Electrical engineer for Loading calculation in case city will ask for it.

Again, a lot of thanks for everybody

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