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I need to know that electrical characteristics are necessary for a network of 20 computers. There are just 20 PCs in a room. There aren't servers and are connected in series.

I just need the information to electrical calculations.

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migrated from stackoverflow.com Dec 8 '09 at 14:55

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1  
Huh? Could you elaborate? Thanks. –  joeqwerty Dec 8 '09 at 14:59
    
More information is required. Like density/proximity of the computers. For instance are these in a rack in a small closet or spread out between 3 buildings with 1km distance between them? Also clarify what it is you need help with. Is it HVAC, power distribution, or networking? –  3dinfluence Dec 8 '09 at 15:13
    
Um...server room or just to run 20 computers? All in one room? You'd have to figure out how many circuits you have available and I suppose you could use a vamp clamp to figure out how much power each of your workstations are drawing and see if it exceeds the load you're putting on your circuit...or the old fashioned way where you turn everything on and if the circuit blows, you're drawing too much amperage. Do you mean in a server room instead? Cooling? Cost? –  Bart Silverstrim Dec 8 '09 at 15:49

2 Answers 2

Don't just sum up the wattage rating of the power supplies. Computers usually draw some fraction of their P/S rating.

Like toppledwagon said, you need readings from something like a Kill-A-Watt. You need idle, light usage (web surfing/reading e-mail) and busy (running you most intensive application) readings from representative computers. That is, if you have 3 different kinds of computer configurations in your lab, you need 3 sets of 3 readings.

Then, sum up 3 totals, all idle (lab during lunch break, all computers on), light usage and heavy usage for all 20 computers.

Now, determine how many circuits you have in the room and what breakers they are on. This is easy. Get a US$10 circuit tester, plug it in and push the button. This will pop the circuit breaker on that circuit. Then, see how many outlets went dead. Repeat until you have identified all circuits in the room.

Take note of the Amp rating of each tripped circuit breaker for each circuit.

Add up ancillary equipment such as your network switchs, projector, etc.

Add up auxiliary loads, stuff that doesn't need to be on UPS- stereo speakers, radios, fans (20 computer labs can get warm in Summer), toaster ovens, microwave ovens, TV's, under-desk foot warmers and anything else that plugs into the wall.

Now. Decide what needs UPS, what needs mere protection, and what doesn't. Consider the power reliability in your area. If it is shaky, put all computers on UPS and everything else on Brick Walls or Tripp Lite Isobar's. If it is very good, put the most critical computers on UPS, the rest of computers on BW/TLI, and everything else on cheap power strips.

Now that you have power under control, you need to consider cooling. Does the room have its own thermostat? Are you working in Toronto or San Jose? Are there windows that open? Are there return vents? Take your wattage sums to your Physical Plant or HVAC vendor and ask them if you have enough tons of cooling to cover the load. Ask them if you need to run the A/C in the Winter. If so, is there another way to distribute the heat?

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You need to get readings on each type of server (hopefully you don't have 20 different types, but if you do you need readings on each.) You can get readings with a Kill-A-Watt or a Watts-Up meter (I like the International version (UO) of the Watts-up because it handles 120-240 input voltages and servers are more efficient with higher voltages.)

If you trying to size a UPS you might want to read APC White Paper #15.

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