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".
4-Pin Molex to PCI-E Power is not a good idea, even if you think that everything should be fine with the cables you have available and make sure you do not overload the power lines on the PSU... then suddenly the connectors on the cables start failing you.
More up to date yet similar problem are the SATA power to Molex power adapters, though there is a solution for that as well in order to minimize the possible issues: http://cryptomining-blog.com/8792-dual-sata-power-to-4-pin-molex-power-adapter-cable/