Types of Electrical Extension Cords

Most extension cords have plugs with either two or three prongs. Two-prong plugs aren't grounded, while three-prong plugs are. The third prong, which fits into the round hole beneath the two vertical slots on a typical 120-volt outlet, leads to the ground wire in an electrical circuit and significantly reduces the risk of electric shock or fire. If a device malfunctions or if loose wires come into contact with a metal case, the grounded three-prong plug would route electricity from the hot wire directly into the ground rather than into your hand. Never attempt to remove or tamper with the third prong in a grounded plug.

When working with electricity in any capacity, it's important to have a basic understanding of amperage, voltage and wattage. Amperage refers to the current of electrons that flow through an electrical conductor. Voltage measures the electrical force that puts the electrons in motion. Wattage measures the electricity used. When you multiply the number of amps by the number of volts, you get the number of watts. Extension cords are designed to handle only a certain amount of amperage, which is why it can be dangerous to connect devices with a higher current. Energy requirements for most electrical devices are usually listed on the device itself or in the manual. When choosing the right extension cord, make sure that the cord has an amperage or wattage rating equivalent to the device that it will be used to power. Connecting multiple devices to the cord at the same time will increase the energy requirements, so don't forget to calculate for the additional current.

The size of the copper wire that delivers power inside an extension cord is called its American Wire Gauge (AWG), or gauge for short. A low AWG number indicates a thicker wire and a greater capacity to deliver power, whereas a higher AWG indicates a smaller wire with less capacity. The most common extension cords come in 16, 14, 12 and 10 gauges. The 16-gauge cord is a light-duty extension commonly used for general purposes like powering work lights, portable fans or hedge trimmers but should never be used for high-powered loads. The 10-gauge cord is an extra heavy-duty extension with the highest capacity to deliver power, making it the best choice for big power loads like chain saws, table saws and circular saws. Lower AWG numbers carry power over longer distances without dropping voltage, which is an important consideration, especially when powering appliances that have a motor. Running a motor on insufficient voltage is a surefire way to put yourself in the market for a new motor, so always choose an extension cord with the lowest AWG for motored devices.

The length of the extension cord is another important consideration. Since voltage is lost across distance, shorter cords are best for running devices with higher current requirements. Using shorter cords is usually fine for most appliances, as substituting a longer cord for a device with a higher current could damage your equipment or pose a safety hazard. When in doubt, go with the shortest cord.

Many extension cords come with a built-in ground fault circuit interrupter, or GFCI for short. The GFCI adds another layer of safety because it's designed to automatically cut power to the cord if a ground fault occurs.

Extension cords are designated for indoor or outdoor use depending on their design. Cords designed for outdoor use boast covers made of weather-resistant materials like rubber, plastic or vinyl. While outdoor extension cords can safely be used inside, never use indoor extension cords outside since this can lead to overheating and increase the risk of shock or fire.