In a comment you say you're worried about shorts between live wires and ground, causing high currents. But in your question you say you maybe want
a switch that activates only when high voltage is supplied, diverts the flow and grounds it, and then closes?
This is unlikely to work because when there's a short from a power net to ground, it tends to cause the voltage on the power net to fall (due to resistance of the power wires), not rise. In any case, the behavior you ask for is essentially a short from power to ground.
It's not clear to me how shorting power to ground would protect you from shorts between power and ground. However if I've misunderstood your requirements and you really do want this behavior, what you're looking for is called a crowbar circuit.
One thing that might help you is a polyfuse or resettable fuse. These work like fuses, in that they increase their resistance dramatically when current rises too high, typically shutting down the load. Their advantage over a traditional fuse is that they revert to normal operation after cooling down, so they don't have to be physically replaced every time they operate.
However like fuses, they may take tenths of a second or seconds to operate, which could be too long to avoid damage for some sensitive equipment. Fuses are not really meant to protect your equipment, just to stop it catching fire and damaging things around it.
Another option would be to modify your power supply to include overcurrent protection. Linear Technology, for one, offers several regulator ICs with an overcurrent protection feature.