Electrical Projects The three-wire electrical service in most homes in the United States was designed to minimize shock hazard. In most foreign countries, a two-wire 200-240V service is provided which increases the shock hazard Although the domestic three-wire service supplies 240V, it also provides 120V. The potential across wires A and C is 240V. But across wires A and B and across wires B and C, the potential is only 120V. Since wire B is grounded, the maximum potential with respect to ground is 120V, not 240V.

Nevertheless, there is a shock hazard. If a person touches a defective appliance whose electrical circuit at some point is grounded to its metal case, the person can suffer a lethal shock when standing on a moist floor or touching a grounded object when also touching a metal part of the appliance. Although such an appliance might work okay, it can be dangerous to use and should be repaired.

October 12, 2008