Electrical Projects A very small leakage current normally flows from the electrical circuit through the insulation material to the exposed metal parts of electric appliances and power tools. Since the insulation material can break down due to age, wear, moisture content, or other reasons, it can allow higher leakage current to flow. This leakage current can become great enough to be lethal to anyone touching the metal surface of the appliance while at the same time contacting a grounded object such as a water pipe, radiator, etc., or when standing on a wet floor. Therefore, it is extremely important that the leakage current of ac appliances be measured before and after servicing or repairing.

The leakage hazard is minimized when a three-way power cord is used with the appliance and is plugged into a polarized outlet whose third connector is properly grounded. The effectiveness of this arrangement dep>ends upon the wiring and upon the appliance having a good ground connection.

The Underwriters Laboratories and the American National Standards Institute recommend that the leakage current of 120V ac appliances be limited as follows: appliances with two-wire power cords, 0.5 mA; portable appliances with three-wire power cords and third wire grounded, 0.5 mA; nonportable appliances with three-wire power cords and third wire grounded, 0.75 mA.




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Home > Electrical Projects > Tools And Components > Appliance Leakage Tester

October 6, 2008