S7 pulls approximately 1.4KW so for a 240V setup (you definitely don't want 120V, too troublesome for high-current loads) you're looking at 6A per miner. Four miners will run fine off a 240V 30A circuit.
If you're wanting to divide that up, I'd recommend a pair of 20A circuits because that gives you room for expansion (20A can support 3 miners).
I recommend server PSUs. For the record, I sell server PSUs - I don't recommend them because I sell them, I sell them because they're generally a more reliable and cost-effective option than consumer ATX supplies. For one miner a good DPS1200 kit will work; if you want more juice, talk to Finksy or Optimizer for heavier-duty supplies that can run two or three miners together.
Going with a server supply kit usually means a bit more hands-on, but it's also a lot more modular so if something does go wrong it's cheaper and easier to maintain than replacing the entire thing like with a consumer PSU.
Bitmain also makes decent supplies; the 1600W APW3 is okay, but I have no experience with the newer bigger one they released a few months ago.
240V has a buttload of different outlets even for the same general power requirement. Depending on the PSU, you're looking at either a C13 or C19 end (both are very standard, very common). Make sure to use outlets for which you can find cables to fit the PSUs.
I'll second the Server PSU's.
I run all my miners on DPS-1300 units all seconds from eBay about £15 each.
I use two per miner on the S7's and S9's.
One PSU to run 2 hash cards and one for the third card and the controller.
I'm a qualified sparky and the power miners draw even got me worried.
Now I have a purpose installed 63A 3-Phase supply with a mains board mounted directly on the rear of the miner rack.
Each PSU is hard wired into a switch fused spur with a 10A fuse in each.
I use two per miner one for each PSU.
Each pair of spurs is wired in 4mm singles to a 10-Amp single pole breaker.
One thing I learned in the first week was extension leads and UK plugs get hot and melt.
The noise doesn't bother me as they all sit in my unit at work.
The heat on the other hand...........
It's ok at the moment as the weather is cold but the unit gets soooooo warm in the summer I worry like hell the rigs gonna melt.
Lol. Remember getting six Spondoolies SP20's a while back and throwing them in the Server room at work I confess I didn't have a clue.
Next day you could have baked bread in the Server room and it ruined the A/C and took our website down as the Supermicro rack Server decided enough was enough. One Dl360 made it but the office DL80 died of heat stroke.
That day cost me a lot of money but hit home HARD the power of mining......
