The role of Zinc blocks

Zinc blocks are widely used in electronic circuits, because of the protection circuit to damage the instantaneous voltage power supply system of the mutation may be. When the high pressure comes, the varistor resistance decreases and current shunt to be safeguarded against excessive transient voltage damage or interference. Thereby protecting sensitive electronic components.
However, I do not think the role of the varistor too, varistors are not able to provide a complete voltage protection varistors can withstand the energy or power is limited, do not provide sustained overvoltage protection . Sustained overvoltage will destroy the protection device (varistor), and damage to equipment, and there may be a fire hazard.Zinc Oxide block not provide protection part are: the inrush current at power-on, over-current short circuit, voltage dips, etc., these cases require other forms of protection. In addition, there are a few protection device detects the power supply voltage, such as the power supply will be cut off when the relay exceeds dangerous limits.