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 10-06-2003, 04:37 PM #1 BrianK Senior Member   Registered: Mar 2002 Location: Los Angeles, CA Distribution: Debian, Ubuntu Posts: 1,334 Rep: Electrician question - how many amps for a 10-20 machines? New power is being run into my new office... My machine room will have a minimum of 11 machines and a maximum of 18 machines. Looking at the Antec webpage, it says that the Truepower 430 Watt PS's require 9 amps - I know I've had more than three computers on a 30 amp circuit, so what is the formula for figuring power requirements of the building? Assuming I have 15 machines running the above PS, what sort of amperage do I need on the circuit(s)? Do I really need to have them run 135 amps to my machine room? That seems like an awful lot. Last edited by BrianK; 10-06-2003 at 05:01 PM.
 10-06-2003, 04:52 PM #2 ehdwuld Member   Registered: Jul 2003 Distribution: Currently Suse 11.1 but have RH7,8,9 / Fedora 7,8_64,9_64,&10_64 Posts: 634 Rep: depends on the size of the pwer supplies and voltage E ------- I x R E = voltage I = amperage R = resistance watts P ------- I x E P = watts I = amperage E = voltage
 10-06-2003, 05:00 PM #3 BrianK Senior Member   Registered: Mar 2002 Location: Los Angeles, CA Distribution: Debian, Ubuntu Posts: 1,334 Original Poster Rep: hmm.. yeah, i knew about those formuls from my circuits classes in college, but that still doesn't help out too much. I don't know how to measure resistance in this sort of an environment, and I don't know if the input amperage reading is a measure of what the PS actually requires to run, or if its a peak value, or what.
 10-06-2003, 05:07 PM #4 ehdwuld Member   Registered: Jul 2003 Distribution: Currently Suse 11.1 but have RH7,8,9 / Fedora 7,8_64,9_64,&10_64 Posts: 634 Rep: get a copy of " Ugly's Electrical Guide " yea thats really the name has charts for measureing reststance by guage of wire verses length copper vs aluminum all sorts of other interest stuff small pocket-sized yellow book with red plastic binder in the electrical section of Home Depot
 10-06-2003, 05:33 PM #5 Blinker_Fluid Member   Registered: Jul 2003 Location: Clinging to my guns and religion. Posts: 683 Rep: One thing to consider is you are not going to be running full power all the time so 9 amps per computer is probably overkill... From experience I would probably guess closer to 3 amps/computer unless you're running something really hot (dual power supplies etc) Don't forget about switches etc also and it's always better to have some extra amps just in case...
 10-06-2003, 05:36 PM #6 BrianK Senior Member   Registered: Mar 2002 Location: Los Angeles, CA Distribution: Debian, Ubuntu Posts: 1,334 Original Poster Rep: ok... we may be on the right track here... so if I know the wattage and the voltage, I can figure amps.... That said, if I have a 400W PS, do I assume that it's going to be drawing 400W all the time? edit: Thanks blinker - you answered before I asked.... how kind of you. Last edited by BrianK; 10-06-2003 at 05:42 PM.
 10-06-2003, 05:44 PM #7 Blinker_Fluid Member   Registered: Jul 2003 Location: Clinging to my guns and religion. Posts: 683 Rep: You shouldn't be pulling 400W all the time. I believe 400W is Peak draw.
 10-06-2003, 06:06 PM #8 WingNut Member   Registered: Jun 2002 Location: Texas Distribution: Slackware 10.1 Posts: 105 Rep: . Last edited by WingNut; 10-06-2003 at 06:08 PM.
 10-07-2003, 02:22 AM #9 faheyd Member   Registered: Jun 2003 Location: Northern California (NorCal) Distribution: Ubuntu 7.04 and DSL/Puppy etc Posts: 342 Rep: When you have a 'power out' and then power is restored, you are going to get a large power draw upon machine bootup, when the power supply surges in each computer. 450w / 110v = 4a , but when it surges upon boot, I'm sure you will draw more than the 4a, maybe even 6 or 7 amp. So I would get a 200amp service brought into the machine room. You can run plenty of 20 amp circuit lines to your benches and equipment racks. Probably 4 or 5 boxes per circuit should be about max, so about 200/20= 10 lines of 20 amp service, but just install what you need to the racks, leave some for a spares and for separate 20 or 30 amp (UPS's or other large devices) service. This will 'future' proof your machine room, as you'll never know exactly what the future may bring. Remember, pay for a 'contractor' only once for the big job, the materials themselves are cheap in comparision. Look at it this way, get more than you need, and you'll not have to have the contractor come back for an upgrade next year.
 10-07-2003, 12:49 PM #10 BrianK Senior Member   Registered: Mar 2002 Location: Los Angeles, CA Distribution: Debian, Ubuntu Posts: 1,334 Original Poster Rep: Wow, great information faheyd. Thanks!

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