The difficulty comes when trying to measure current draw of your computers (The max watts on a PSU are only output; for max current input you need to consider effeciency among a few other things including the actual output power). I'd estimate my computer (a nice over-clocked dual cpu workstation) draws 5-7 amps @ 120vac including monitor.

In general you can expect to safely toss ~5-6 computers onto a 20 amp circuit without tripping the breaker. I'd recommend using several outlets though (no daisy-chaining) because I've seen powerbars melt before when 10+ people daisy-chain off of each other. You might be able to squeeze 8 people, but if your buddy has substandard electrical wiring and run close to the max current for many many hours the resistance in the wiring can build up quite a bit of heat.

In one of the largest LAN events in my state (I think one year we approached/broke the state record with perhaps 70-80 people?) we actually had the electrical company install some *really* heavy duty wiring and a voltage transformer so we could power up ~70 machines, a projector, and concession stands. No electrical issues that time. But this setup was nothing compared to the warehouses with 200-500+ people in Texas duking it out on the weekends.


So you should be able to support 5-6 friends on a 20amp circuit. If you need more people, bring power in from another room/circuit but put less load on it over the extension cords to be safe.