I've only got a dedicated 120V/60A/8kW circuit here so need to make do with that.  If I ever need more than 8kW/60A I'll get them to quote for 240V as well.

Why a 20A circuit?  The S9 14TH/s model is rated at just under 1400W at the wall, ie about 12A.  I was going to wire each into its own 15A breaker with 8 AWG. With either an individual or group RCCB/RCD.

I'm very nervous about the multi PSU idea, seems a PSU failure could kill the S9?

Parallel Miner looks interesting, thanks!  Seem to open up a whole new bunch of PSUs to use.