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I apologize in advanced for my poor technical lingo.

I have a spare house which is strictly using electricity to power some servers. I'm slowly building out a cluster, but before I move it to a warehouse I want to have everything up and running and profitable.

Right now I use about 2 KW, I have them on various circuits through out the house so it doesn't trip the breaker.

I live in the USA, I think I saw 100 Amp, 50 Amp, and 20 Amp breakers, so theoretically I could run at least 12 KW. If I had an electrician modify the circuit breaker so all the servers ran in the garage, which is 20 feet away from the breaker.

I'm looking at cost efficiency, I don't want anything permanent done, no rewiring the house or anything, just a temporary setup while I build up capacity. The wiring could be laid on the floor instead of the walls & attic. All it needs is standard wall outlets to plug in the servers.

I'm concerned about two things, obviously safety, and cost. I kinda want to do it myself, I'm interested in learning/doing these things, and I have a background in Mech and Software engineering. Preferably I'd watch and learn from an electrician, how much would you estimated it cost for it to be done? Anything I should know about my plan?

I live in a very low cost standard of living state so I imagine it won't be too much.

Thanks!


Additional information:

Each server uses about 1200W continuously. They're running as a generic desktop configurations. they're not standard generic servers for a server farm, so they use a standard 120V supply.

I have taken into consideration HVAC, and plan to use a large fan to push the hot air out the garage door, as a temporary setup. So accounting for the 20% max load rule, I figure I can run 8 rigs.

Also, the electric box on the outside of the house said 100 AMP, the circuit breaker doesn't have any labels, it's a 40 year old house. Nothing else will be running, Dryer, AC, Electric Stove, etc. Also wouldn't the 20 AMP breakers in the garage/kitchen run on the 240V circuit? Wouldn't it be costly to convert it to 120V?

Spacing it in my house to run off each circuit probably is the best cost efficient idea, but I'm not too keen on running 8 Ethernet cables throughout the house as a potential hazard, and moving a monitor through the house for any maintenance is a pain.

If an electrician did come out and rework a temporary garage setup so I can run 10 KW from the garage, how much is a rough guesstimate for the cost? I'm trying to factor it into my plan before I make any hard decisions.

Thanks guys, you've been very helpful!

  • These "1200 watt" servers... Are you quite sure they are 1200W actual, and not 960W actual? Measure its VA with a Kill-a-Watt while it's at full load, you can use that load figure. Server makers are acutely aware of the 1440 and 1920 watt limits, and it seems unlikely they would paint you into a corner like that. Well, anyway, eight 15A or 20A 120V circuits will do the job, your house will have that. Also stop worrying about 120V vs 240V, the panel automagically takes care of that for you. Is there some flaming reason you absolutely need to put these things in the garage? – Harper - Reinstate Monica Jun 14 '17 at 1:52
  • @user70829 Please merge your guest and registered accounts, which will allow you to edit, comment on any of your posts and accept an answer on your question. Thanks, and welcome to the site! – Niall C. Jun 14 '17 at 2:36
  • What's the ethernet throughput actually used? Would powerline ethernet suffice? – RedGrittyBrick Jun 14 '17 at 13:06
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Your house already has all those circuits. Look at your breaker panel at all the single-space (1 pole) breakers. Almost all of them are 15 or 20 amps. A 20A breaker can drive 1920 watts on a continuous load. A 15A breaker can carry 1440W on a continuous load. Worst case, at 1200W per circuit, you'll need eight 120V circuits, and your house will have that.

You are saying 1200W but that is just a common nameplate rating on a PC power supply. You can buy a "Kill-a-Watt" power meter and measure the actual load when the server is at max performance. Read the VA number and use that in place of watts. For instance if the server reports 900 VA actual, you can put two on a 20A circuit.

Your kitchen has two of the 20A jobs. Your garage probably has another 20A. They're all over the house.

If you don't know what breakers serve what receptacles, get some night lights at the dollar store and plug em in all over the place. Then turn on one breaker at a time and walk around and see what lights up. You can turn on several breakers at a time or even half the panel, and then you can make a logic game of it.** Things which DO light up are on that circuit. Things which DO NOT light up are on a different circuit. Feel free to cover your receptacles with Post-its.

Crowding all that equipment into the garage, and paying a guy to run a bunch of cable, is silly. Not least, the garage location will require GFCI breakers since this will be new work.

Also by putting it in the house proper, your A/C units will come to bear.

** if you have <32 breakers, you should be able to match up every outlet in five loops through the house. Print out a bunch of sheets of paper with the numbers 1-32 on them. First you set odd breakers on, and loop through the house. Strike out (exclude) even numbers if it's on, or odd numbers if it's off. Next turn on every other pair: 1-2, 5-6, 9-10 etc. and cross out the circuits the outlet can't be. Then every other group of four: 1-4, 9-12, etc. Two more rounds, and each sheet of paper will have only one number remaining.

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Depends a great deal what we're talking in terms of servers. Based on this Quora answer a full 48U rack can draw 5-30kW, depending on how much computing power you're using at the time. He also notes that most datacenters use 208v, not 110.

Some rules of thumb off the top of my head:

  • A single-phase 208V*/30A circuit has a maximum server load draw of about 4.9kW.
  • A single-phase 208/50A circuit has a maximum server load draw of about 8.3kW.

Then you need to consider cooling. I would recommend a mini-split AC, but a window or upright unit might work. Then you're going to have network cabling, switches, routers, etc.

I'm not sure what you're proposing is practical (and might be a classic XY Problem). You might be better off getting co-location now and avoiding the headache of trying to rewire for a homemade datacenter.

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Standard circuit breakers are not rated to carry 100% of their labeled ampacity continuously. Continuous loads are loads that run for three hours or more at a time. Servers would be a continuous load. Breakers with continuous loads should only be loaded to 80% of their rating.

Therefore, a standard 20 amp 120 volt circuit can handle 16 amps or 1920 watts. About six, three hundred watt power supplies per circuit. Lower powered servers give you more per circuit. However, six of these fully loaded would be 96 amps and might trip a 100 amp breaker after an hour or more. This would give you 36 servers or so on a 100 amp sub-panel. This all depends on the draw of your server power supplies.

Temporary wiring can be run with hard usage cord but should be kept away from any exposure to physical damage or creating a tripping hazard.

You might also have a heat problem from all those servers. You may need air conditioning to maintain the temperature.

  • The OP's notion of temporary ("till profitable") and NEC's notion of temporary are incompatible. – RedGrittyBrick Jun 14 '17 at 13:16

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