Computer workstation loads

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JRCJ

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Can someone tell me how many Amps does a typical computer workstation draw? Typically we design 2-3 isolated grounding type receptacles per 1P20A circuit for computer workstations. Looking at a hard drive it lists 6.5 amps and 1 amp for the monitor but I have been in existing offices where they have 6-7 workstations on the same circuit and it doesn't trip the breaker.
 
I've had the same problem when designing call centers. I tell the owner 3 per circuit based on nameplate information, and he says "yea but at my other place I have 10 on a circuit."

The load will vary depending on devices, but an actual load of around 3 amps is probably accurate. I'm not sure you can design based on that though, because the nameplate does say 6 amps.

Last note, I don't use IG's for nearly any computers anymore. What is your experience recently?

Jim T
 
The last time I designed a facility that included office spaces, I used one "full boat" (A, B, C, N, G on a 120/208 system) to serve six offices. That worked out to an average of two offices per circuit. But that included receptacles intended for the computers as well as general purpose receptacles on the office wall spaces. It was a design choice on my part, and the owner did not object.
 
Re: Computer workstation loads

JRCJ said:
Can someone tell me how many Amps does a typical computer workstation draw? Typically we design 2-3 isolated grounding type receptacles per 1P20A circuit for computer workstations. Looking at a hard drive it lists 6.5 amps and 1 amp for the monitor but I have been in existing offices where they have 6-7 workstations on the same circuit and it doesn't trip the breaker.
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Besides the workstation draw you need another 20A circuit for the 1500W heater everyone has in their offices.

In the office I work at, we have a 20A circuit for each office.

Adds a few breakers, but makes it near impossible to trip a breaker, although I did once.
 
Hard to say whats "typical".

A high end graphics card can suck 150W all by itself. Something cheap/slow sharing RAM with the system may only be a few watts.

Some generations of Pentium 4 CPU consumed as much as 115W each.

If these are engineering workstations with dual/quad CPU's, a bunch of SCSI drives on a RAID card, etc, it would be very easy to bust 1000W/station when you figure tape backups, printers blah blah blah and that's not figuring in a monitor yet.

If its a cheapo $400 box doing a RIPL off a LAN with no local storage at all, then you may only be in the 200W range(or less).
 
jtester. Thanks for you input. I haven't had any problems (that I know of) providing I.G. outlets for computer workstations. Out of curiousity why don't you put them anymore?

petersonra. I live and work in Hawaii so I don't think I need to worry about the 1500w portable heaters under peoples desks! ha ha.
 
tonyi said:
Hard to say whats "typical".

A high end graphics card can suck 150W all by itself. Something cheap/slow sharing RAM with the system may only be a few watts.

Some generations of Pentium 4 CPU consumed as much as 115W each.

If these are engineering workstations with dual/quad CPU's, a bunch of SCSI drives on a RAID card, etc, it would be very easy to bust 1000W/station when you figure tape backups, printers blah blah blah and that's not figuring in a monitor yet.

If its a cheapo $400 box doing a RIPL off a LAN with no local storage at all, then you may only be in the 200W range(or less).
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Tonyi.
Thanks. You have a good point. It would be really hard to assume what people are going to be running at their workstations. Plus a lot of people have extra external equipment too such as back up hard drives, burners, etc...
I have always struggled trying to figure an accurate load especially when I'm designing an existing renovated office space. Right now my dilema is that I have an existing 208/120v panel with a 3P150A main that sub-feeds two existing panels with a 45KVA transformer. When I apply 180va per outlet and do my first 10kva at 100% and then then remainder at 50% it comes out close.
 
I think they need to give you a clue as to what the planned occupancy per office is. No matter what the code says to calc for, if there's two people in the office you can probably realistically plan on doubling the VA/recepticle load. In Boca, IBM always packed two grunt engineers per office.

Some years ago I did a short computer consulting gig at BN.com and they had about 10 of us hired guns packed into a normal office shoulder to shoulder. I'm sure whatever breaker was serving that room was right on the ragged edge of tripping...or more likely was illegally replaced by a 30A :lol:

I don't miss any of that stuff. I enjoy doing real work now :D
 
6.5 amps for a hard drive, that sounds very high. Typically the monitor pulls the must juice, 1amp(100watts) sounds about right. Are you sure you weren't looking at the amperage for the 12 volts that the hard drive runs on? that would put 120 amps at 0.65
 
charlie b said:
The last time I designed a facility that included office spaces, I used one "full boat" (A, B, C, N, G on a 120/208 system) to serve six offices. That worked out to an average of two offices per circuit. But that included receptacles intended for the computers as well as general purpose receptacles on the office wall spaces. It was a design choice on my part, and the owner did not object.
Click to expand...

Did you have a concern for harmonics with the computers? If so, do you remember how you sized the neutral?

Thanks,
Lou
 
I haven't had any problems (that I know of) providing I.G. outlets for computer workstations. Out of curiousity why don't you put them anymore?
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I don't see a benefit with IG's in most applications, for instance where pc's are on peoples desks. Sometimes an IT guy will insist on isolated grounds, and I am happy to specify them, but they are relatively expensive and I am unsure of the benefits.

Jim T
 
Computer Power

Computer Power

:)Typically a PC workstattion is composed of a CPU box and a monitor. The CPU case has typically one power supply. If you look at the power supply label you can have an idea of the maximum power the box will draw. A good average is 250W max per CPU Case. The monitors add 150W max average.
Do not get confused with the AMPs inside the box for the Hard Drive and CPU. These are DC ratings and it is not a constant value. Typically I go no more than 6 Workstations (CPU box and Monitor) on a 20A breaker. You have to account that at anytime someone may add a color laser printer next to their PC on a power strip and you do not want be called in for a free service call.[/code]
 
I have a 300 watt power supply in my PC and it is a pretty much low end unit. I see a push to 350-450 watt power supplies now.

A laser printer can have a pretty significant power draw at times.
 
500W supplies will be the norm before too long, but does that mean thats what an office computer will draw, not likely.
400W for monitor and case is a good figure, but with 6 on a circuit you're right at 20 amps. Which raises the question of continuous load, the computers are on all day, but are only drawing full power for a small portion of that time.
We don't put more than 4 computers on one circuit.
 
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