You can build an overvoltage protection circuit using metal oxide varistors (voltage dependent resistors) or any fast semiconductor based component, such as Zener diodes.Metal Oxide Varistors (MOVs) or Voltage Dependent Resistors (VDRs):
Varistors offer a large voltage surge-handling capability, but a delayed response time. In the following circuit, the MOVs will shunt the current to the GND lines when the surge exceeds the MOV's rated voltage.Zener Diodes:
Zener Diodes have a better response time over MOVs, but can only handle a small amount of current. The resistors in the diagram below will prevent a large surge current from damaging the diode.