When an electrical system is not grounded properly, a hazard exists. The most common OSHA electrical violation is improper grounding of equipment and circuitry. The metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be grounded and at 0 volts. If the system is not grounded properly, these parts may become energized. Metal parts of motors, appliances, or electronics that are plugged into improperly grounded circuits may be energized. When a circuit is not grounded properly, a hazard exists because unwanted voltage cannot be safely eliminated. If there is no safe path to ground for fault currents, exposed metal parts in damaged appliances can become energized.
Extension cords may not provide a continuous path to ground because of a broken ground wire or plug. If you contact a defective electrical device that is not grounded (or grounded improperly), you will be shocked. You need to recognize that an improperly grounded electrical system is a hazard.
Electrical systems are often grounded to metal water pipes that serve as a continuous path to ground. If plumbing is used as a path to ground for fault current, all pipes must be made of conductive material (a type of metal). Many electrocutions and fires occur because (during renovation or repair) parts of metal plumbing are replaced with plastic pipe, which does not conduct electricity. In these cases, the path to ground is interrupted by nonconductive material.
A ground fault circuit interrupter, or GFCI, is an inexpensive lifesaver. GFCI’s detect any difference in current between the two circuit wires (the black wires and white wires). This difference in current could happen when electrical equipment is not working correctly, causing leakage current. If leakage current (a ground fault) is detected in a GFCI-protected circuit, the GFCI switches off the current in the circuit, protecting you from a dangerous shock. GFCI’s are set at about 5 mA and are designed to protect workers from electrocution. GFCI’s are able to detect the loss of current resulting from leakage through a person who is beginning to be shocked. If this situation occurs, the GFCI switches off the current in the circuit. GFCI’s are different from circuit breakers because they detect leakage currents rather than overloads.
Circuits with missing, damaged, or improperly wired GFCI’s may allow you to be shocked. You need to recognize that a circuit improperly protected by a GFCI is a hazard.
Notes:
■ fault current—any current that is not in its intended path
■ ground potential—the voltage a grounded part should have; 0 volts relative to ground
■ If you touch a defective live component that is not grounded, you will be shocked.
■ GFCI—ground fault circuit interrupter—a device that detects current leakage from a circuit to ground and shuts the current off
■ leakage current—current that does not return through the intended path but instead "leaks” to ground
■ ground fault—a loss of current from a circuit to a ground connection