A device protecting electronic equipment from surge (abnormal voltage) is called a Surge Protective Components (SPC). SPC protect from entry of surge between 1 the line to line interval or 2 the interval from the line to the ground.
SPC typically has a high resistance level and most of the electric currents do not flow (nor influence the electronic equipment). However; when surge (abnormal voltage) enters, the Surge Absorber instantly eliminates surge with low resistance to protect the electronic equipment. When surge is eliminated, the Surge Absorber returns to high impedance.