The basic strategy for any overvoltage protection scheme is to place the protector in parallel with the protected circuit. Voltage in an electrical circuit is analogous to pressure in a plumbing system. The overvoltage protector then functions as a kind of high pressure safety valve. The protected circuit is not designed to handle voltages above a certain level. Forcing these circuits into conduction with high voltages can damage them permanently. The overvoltage protector, on the other hand, is specifically designed to breakdown at a certain voltage level and conduct large amounts of current without sustaining damage. The challenge is to insure that the overvoltage protector will break down before the protected circuit and safely redirect the unwanted energy away from the protected circuit. In a sense, there is a race between the overvoltage protector and the protected circuit to breakdown in the face of a rising voltage.