Overvoltage protection devices can be divided into two classes. First Clamping devices limit the voltage to a fixed level. In doing so, they absorb the excess energy of the overvoltage event as long as the event is present. TVS diodes are an example of clamping devices. Second Crowbar devices, once triggered, essentially short out the protected line, redirecting the excess energy away from the protected circuit. Once the overvoltage event has stopped, crowbar devices will “delatch” and allow the circuit to resume normal operation. Because crowbar devices short out the protected line when activated, it is used only in applications where the available power is limited – such as telephone circuits, data lines and signaling systems. TVS devices are all clamping devices.