In stock mode with the ASICs at 218.75, how much power does an S3 pull? The OP says 366 watts, while dogie's guide says 340. If it's 340 I should be able to run 4 S3's off of one regular 120v circuit right? 340x4 = 1360 watts. That's about 75% utilization of power... Should be within the safe zone..
On a 120V Grid Supply, you can run as much S3 as your money can buy.
What matters is the available Ampere to your house or farm.
For 120V the PSU efficiency is lower than 230V.
Multiply your 120V with the maximum available amps which allow through your breaker.
Make up your S3 power consumption to 125% and divide it from your above figure.
The number you got now is the maximum no of S3s you can run maximum or that's the maximum load you can have through that beaker.
For example if your house have 100A/120V and through a 20A breaker,
20A*120V=2400W
340W*125%=425W
2400/425=5.6 = 5 S3.