To the moon for ETH please!

Gotta agree that it sounds like a power supply issue, but as notlist3d suggests I would test one hash board independently of the other and see if one or the other is causing any issues.

No problem! None of my breakers are GFCI types, but I do use a set of GFCI protected outlets at my electronics workbench and that is where I'm currently running two Antminer S3+ units. I actually found that my circuit breaker was too old and vibrating horribly and had to be replaced, but my GFCI is holding up just fine.

What is your power supply configuration? It sounds like your controller board is being powered properly, but maybe your ASIC blades aren't for some reason.

AntMiner S5: 590 watts
AntMiner S7: 1,422 watts

Assuming a power supply efficiency of 80%, the S5 would consume 708 watts from the wall, the S7 would consume 1,707 watts.

The total for 7 S5 units and 1 S7 unit would be 6,663 watts. On a 240 volt circuit, this would be 28 amps of current.

A 50 amp circuit should be sufficient to power this with a wide margin, so I would suggest verifying there aren't any additional loads like a hot water heater, range, or clothes dryer on the same circuit. Also, the minimum wire size should be 6 AWG from that breaker, any smaller could cause issues.

If it is an old circuit breaker, that could be part of the issue as well.

Also, purchasing a clamp ammeter would be an easy way to check at the circuit breaker the current draw. Here's the one I use: http://www.harborfreight.com/digital-clamp-meter-96308.html

This is exactly what I'm doing. I looked into the GPU situation and quickly decided ASIC was the way to go. I found S3+ units going for $20-40 right now, so I picked up a couple to have some fun with. All academic, but definitely fun!

16 AWG wire is rated for a maximum of 18 amps (or 216 watts). An S7 will have a total consumption of about 1,350 watts.

What I would recommend is using three 600 watt power supplies, with at least two sets of 12 AWG wire going from the power supply to the hashing board.

With two 1200 watt power supplies (I believe that is the rating running only on 240 volts AC), you could use one for 1 hashing board + control board, and the other for the 2 other hashing boards, but you'll want to have four sets of 12 AWG cables on that 2nd power supply to the two hashing boards.

16 AWG wire is way too small and you should not use any Y-splitters.

Based on that breaker and wiring configuration, it is a single-phase 240 volt connection. A three-phase breaker has 3 distinct sections.

The unconnected wire is (as you suspect) your neutral line. If a device operates as a single 240 volt device, neutral isn't used. If a device operates as "two" 120 volt devices, neutral is used.

So, if you have a power supply that supports a 240 volt connection, you can connect one hot to one input, the other hot to the other input, ground to ground, and you should be good to go!

If you have standard three-phase already (4-wire wye) and power supplies that support 208 volts, you should be able to use L1 & L2, L2 & L3, or L1 & L3 to the power supply. If you have a three-phase delta (480 volts), you'll need a step-down transformer to 240 volts (or 120 volts).

Most power supplies support a range of voltages, for example one I have here is 110-120 volts & 200-240 volts compatible. Others I've seen are 100-250 volts.

Feel free to post the power supply make & model and we should be able to figure it out.