Extension cords are a familiar sight in homes and businesses. When a power cord doesn't reach to an outlet, the simple solution is to attach an extension to it. Extension cords were meant to be temporary power solutions or a means for bringing electricity to job sites where no power exists. More often than not, they become a permanent fixture, but the laws regarding safe use of electrical extension cords clearly state proper use, and OSHA, the Occupational Safety and Health Administration, places strict demands on workplace use of extension cords as well.
National Electrical Code (NEC) Rules
Extension cords must not be used as a replacement for standard electrical wiring for a building. Never use an extension cord where it is put through a hole or opening in a wall, inside a dropped ceiling or under flooring. It is against the National Electrical Code to connect extension cord wiring through doorways or other structural openings like windows. Extension cords must not be hidden in any way behind structures, or covered with objects such as rugs. Extension cords must be clearly marked with a maximum amp to keep cords from overheating. Common amperage is 10, 15, 20, and 25 amps depending on the size and number of wires inside the cord.
Extension cords must have clearly marked characteristics to allow users to judge the compatibility of the cord to a project. There are two standard letters indicating type of service: S and SJ. S stands for hard service, and SJ stands for light service. Additional indications following the S and SJ marks include: T for more heat resistant thermoplastic insulation, E for elastomer insulation, a form of thermoplastic insulation with a more rubberlike composition, O for resistance to oil, and W for the ability to resist water and sunlight.
For safety in workplace environments, OSHA demands that extension cords not be used for more than 90 days even as a temporary wiring solution. Daisy chains -- multiple extension cords connected to each other and/or into a multiple outlet extension such as a surge protector -- are also against OSHA regulations. Power strips that are equipped with self-contained fuses can be used as a permanent solution for extension purposes. All equipment must have OSHA-certified approval.