A CLASS A ground-fault circuit interrupter (GFCI) is designed to protect people from potentially hazardous ground faults arising from the use of defective appliances or portable tools. It works by comparing the amount of current going to and returning from equipment. A GFCI protects against current leakage anywhere in a branch circuit and thus protects against fires, overheating, and destruction of wire insulation. It can prevent electrocution. GFCIs are generally installed where electrical circuits may accidentally come into contact with water.