I have been using corsair PSU to all my rigs. This rig has individual PCIE cables for each GPU and riser. Sorry but I fail to understand which cable is wrong. Thanks for your help.
Heat is generated when high currents encounter resistances. These are mostly either bad wires (small diameter) or bad connectors.
If you are confident in the quality of your power supply and use dedicated cables, make sure you don't have bad connectors somewhere. If the connector is loose, it should be replaced.
I'm just saying that a smoke detector is not a good solution because the wires shouldn't melt if everything is done correctly.