2x 6-pin PCIe cables are used to power my Bitfury M board. A few people have had their's go up in flames when using between 500-600w. The three 12V molex contacts on the 6-pin connector themselves are good for 300W or so all combined, so long as your PSU manufacturer doesn't cheap out on them and use a smaller gauge than spec (which seems to happen on occasion).
It shouldn't be a problem if we're all getting seasonic psus.
Yeah, well the issue is that the bitfury team did not anticipate that people would overclock the fuck out of them and thus pushing power draw into the stratosphere. One of my bitfury rigs is drawing 470 watts from TWO seprate 6 pin PCIE connectors. Previous to that I mistakenly ran two 6pins connectors from the same main PSU feeder jack and guess what, the plastic around the connector melted. It was pretty much close to a complete meltdown. At the time the unit was pushing 528 gh so power draw must have been over 500 watts for sure. I can't for the life of me understand why they did not use either 3 separate 6 pin or 3 8pin just to have some headroom cause they should've expected people were going to overclock the units as soon as they found out how.
Oh and I should mention that the PSU that this happend to was a Corsair AX860 which is likely made by Seasonic. I don't know the gauge of the wire they use but if I had to guess I'd say it 18 AWG.
The point that I'm trying to get a cross here is that over-engineering something is a good thing when you can do it without an unreasonable increase in cost.
Also, damn this thread grows like weeds!