Variable resistors or varistors are key electronic components in circuit protection. Varistors move excessive voltages away from sensitive electronic components. Non-ohmic variable resistors are called varistors – ohmic versions include the potentiometer and the rheostat. Metal oxide varistors are the most common type of varistor, compatible with voltages ranging from 11V to 300V. T-Network varistors are also available to protect circuits and semiconductors from noise and voltage surges.