You also have to be careful of those Molex -> PCI-E power cables.
2 years ago, I had milk-create mining rigs setup at a friend's house (he had cheaper power than me, so we made a deal)
One day I noticed one of the GPU's wasn't responding. He said everything looked okay and the other 3 GPUs were mining.
2 days later I stopped by, and found a Molex -> PCI-E power cable had melted!

That was a bit of a wake up call. It would have been terrible if I'd caused his house to burn down! I don't skimp on quality to save a quick buck anymore.

P.S. You have a typo "electricalc ontacts" should be "electrical contacts".