For two Ants, you'd need at LEAST 60A on the 12V rail. I'd say 65-70A would be ideal. That RM850 gives off 70A, so you should be fine with plenty of headroom.
This bitch: CORSAIR HX Series HX850.
But may be something related to the line, I'm not sure.
I have 3 S1's and one Cube.
I have another Corsair 850PSU (I believe it's a TX).
Currently my setup is the following:
TX850W: One Ant, Half Ant, Half Cube
HX850W: One Ant, Half Ant, Half Cube
If I put two Ants in the HX850W the PSU wont start.
The PSUs are connected to two different sockets, those sockets terminate in a single 20A switch.
I`ve got a HX850 supplying two ants at 400mhz. Pulling 860-870w from the wall.
I will soon exchange to 6mm wires, 220V and a 40 A switch, I believe the issue is with the line not the PSU.
So you are running it on 110v? I`v got around 25m of 1,5mm wire from the 60s on a 10amp, but on 220v ofcourse. So i guess that helps.