RV5/440 is a varistor surge suppressor designed to reduce the maximum overvoltage peak value and to limit or even completely eliminate the high pre-damping voltage frequencies, when used with an AC operated conventional contactor for a rated control circuit voltage between 250 ... 440 V AC 50/60Hz or with a DC operated conventional contactor for a rated control circuit voltage between 250 ... 440 V DC. The operation of inductive circuits causes overvoltages, in particular on opening of the contactor coil. The electromagnetic energy stored in the coil during contactor closing is restored on opening in the form of surges, the slope and amplitude of which may rise to several kilovolts. A number of drawbacks are observed ranging from interference on the electronic devices to breakdown of insulators and even destruction of certain sensitive components. Note: A varistor is a resistor whose value decreases to a very large extent when a certain voltage is applied at its terminals. Advantages: - the surge suppressor is clipped onto the top or side part in regards with the contactor or contactor relay base design without change in device overall dimensions. - high energy absorption: good damping - Unpolarized system. Drawback: clipping as from the varistor operating voltage, thus voltage front up to this point.