We're sorry, but OSHAcademy doesn't work properly without JavaScript enabled. Please turn on JavaScript or install a browser that supports Javascript.

715 Electrical Safety for Technicians and Supervisors
Skip to main content

Defective Insulation Hazards

Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber covering insulates wires.

Defective wiring on tools and extension cords can cause fatal electrocutions.

Insulation prevents conductors from coming in contact with other conductors and with people.

Extension cords may have damaged insulation. Sometimes the insulation inside an electrical tool or appliance is damaged. When insulation is damaged, exposed metal parts may become energized if a live wire inside touches them. Electric hand tools that are old, damaged, or misused may have damaged insulation inside. If you touch damaged power tools or other equipment, you will receive a shock. You are more likely to receive a shock if the tool is not grounded or double-insulated. Double-insulated tools have two insulation barriers and no exposed metal parts.

Improper Grounding Hazards

When an electrical system is not grounded properly, a hazard exists.

This is an example of grounding a structure under construction.

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.

Knowledge Check Choose the best answer for the question.

5-7. Double-insulated equipment must meet which of the following two criteria?