Today I discovered one of my 2xMOLEX -> PCIE 8pin adapters had melted quite significantly, I was terribly lucky that the yellow and black wires were separated like they were and melted into each other instead of mixing and shorting out.
I checked the same adapter in my other systems while still running and they were hot! They showed signs of degradation too, some had slight melting going on, some were slightly charred near the connector pins.
What baffles me though is why this is happening. The adapters are of good design (connecting the +12v wires to spread the load evenly) and seemingly of good quality (with each of the wires being AWG 16 both by the writing on the wire and by measuring myself after the melting took place).
By all indication, these adapters should easily be able to handle the load. Especially considering that I was feeding these adapters with 2 AWG 18 molex cables which should have far less amp capacity and those still look as good as new and were cool to the touch.
As for the numbers side of things - the standard defines that the PCIE 8pin should handle a maximum of 12.5 amps. The cards I'm using them for however only draw around 7 amps while fully loaded.
That divided by the 3 12v wires in the cable means that each of the AWG 16 wires couldn't even handle 2.33A, ridiculous.
I'm guessing this has to be something to do with the core material, it looks like plain old copper but...? Not sure what else it could be.