Precautions in operating room include many subjects among which precautions against electrical hazards. The most important electrical hazards are macroshock which refers to the effects of current applied to the body through contact skin, it leads to disrupting physiologic functions in the form of muscle contraction, apnea, ventricular fibrillation and thermal injury. The severity of macroshock depends on the amount of current, duration of contact and skin resistance. Ventricular fibrillation threshold ranges between 100-300 milliamp (0.1-0.3 amp).While microshock is only of concern to the electrically susceptible patient who has a direct external connection to the heart either by a pacemaker wire or a saline filled catheter. Ventricular fibrillation threshold is as little as 100 microampere. Therefore protection against these hazards include electrical ground which means intentionally connecting the power source to earth ground. The electrical power to the home is grounded but to OR is usually ungrounded, the electrical equipment is usually grounded. Isolated power system is another strategy for ensuring safety against electrical hazards. It has been accomplished by means of isolation transformers. The line isolation monitor is a device that monitors the integrity of the isolated power system and alarms in the event that the power system is no longer isolated from ground. Ground fault circuit interrupter is a device for protection of individuals from macroshock in grounded power system. It detects any difference in the current between the hot and neutral sides and immediately interrupts the power.