Metal Oxide Varistors (MOVs) are non-linear voltage variable resistors, and provide clamping to protect against high energy transients and short circuits. MOVs are very popular in protecting electronic circuits from transients in power lines, but can be used in communication lines too. They are common in household surge protectors. MOVs have a non-linear current-voltage characteristic. They are connected from the power or data line to ground and have a very high resistance at low voltage and a very low resistance at high voltage. MOVs have a very fast turn on time (less than 1 ns), meaning they clamp very quickly. They have improved over the years and do not degrade when activated the way older MOVs used to. Some issues with MOVs on a differential CAN bus are that they can have high leakage current relative to TVS devices. The tradeoff for good performance can be high shunt capacitance and the capacitance can be difficult to match between the two needed (one for each bus line). This can create distortions on the bus.