Insulators such as glass, mica, rubber, or plastic used to coat metals and other conductors help stop or reduce the flow of electrical current. This helps prevent shock, fires, and short circuits. To be effective, the insulation must be suitable for the voltage used and conditions such as temperature and other environmental factors like moisture, oil, gasoline, corrosive fumes, or other substances that could cause the insulator to fail.
Types of Insulation
Insulation on conductors is often color coded. Insulated equipment grounding conductors
usually are either solid green or green with yellow stripes. Insulation covering grounded
conductors is generally white or gray. Ungrounded conductors, or “hot wires,” often are black
or red. However, they may be any color other than green, white, or gray.
Before connecting electrical equipment to a power source, it is a good idea to check the
insulation for any exposed wires for possible defects. Insulation covering flexible cords such as
extension cords is particularly vulnerable to damage.
The insulation that covers conductors in non-construction applications is regulated by 29 CFR
1910.302 through 1910.308, Wiring Design and Protection. Subpart S generally requires
insulation on circuit conductors. It also specifies that the insulation used should be suitable for
the voltage and conditions. Conductors used in construction applications are regulated by 29
CFR 1926.402 through 1926.408.