That is exactly why I only run 3 cards per setup. One psu for the whole thing, no linking a bunch of psu's together, NO POWERED RISERS, 0 problems. These 3 card rigs pay for themselves very easy and you don't have to put up with all the horseshit. I would not have a powered riser anywhere in my house. You don't need them if you don't put 500 gpu's on a 100.00 mobo. Get a good Asus mobo, get one 1050 Seasonic Gold PSU, and 3 280x or 290's or 7950 cards and you will have none of the fireworks, remember, powered risers are not needed at all.
3 GPUs per rig is a waste of space and money if you ask me, but to each their own.
I have never had a single riser burning issue and I've connected over a 100 GPUs to various rigs (6 or 8 cards).
The "secret" is to power risers with molex or pci-e cables and avoid the shitty sata connectors that are just molded on the cables. The real risk is to have 2 cables inside the connector melt together. These connectors and sata cable are not rated for high amperage. Also do not power more than 2 risers per molex cable. Get at least ver 006 risers.
With a good quality PSU (do not go cheap on PSU) you're fine.
And just some basic safety rules: avoid to place rigs near water sources or materials that are easily flammable. I've seen some people on here stacking like 10 rigs in a room on the
carpet floor. That's just asking for trouble.