What varistors don't do?
A MOV inside a TVSS device does not provide equipment with complete power protection. In particular, MOV device provide no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device.
A varistor provides no equipment protection from inrush current surges (during equipment startup), from over current (created by a short circuit), or from voltage sags (also known as a brownout). A varistor neither senses nor controls such events. Susceptibility of electronic equipment to these other power disturbances is defined by equipment design. Protection from these power disturbances is installed inside that equipment or is provided by other external devices such as an UPS, some voltage regulators and Surge Protectors with built in over voltage protection that make use of a voltage sensing circuit and a relay for disconnecting the AC input when voltage reaches a danger threshold.
