Unless you are always lucky enough to have an electrical outlet positioned exactly where you need it, you almost certainly use electrical extension cords around your home. However, most people don't understand just how dangerous it can be to use the wrong kind of cord. The U.S. Consumer Product Safety Commission has found that extension cords are among the most dangerous electrical devices in our homes, due to improper cord sizing and use. Each year, accidents from extension cords kill around 50 people, result in 4,000 injuries requiring hospital treatment, and cause more than 3,000 residential fires. Most extension cord failures can be prevented simply by using the right type of cord for the job.
Even the best extension cord for the job can be dangerous if damaged: Never use a damaged extension cord and plan to replace it immediately.
Why Extension Cords Are Dangerous
An extension cord essentially is a bundle of insulated electrical wires with a plug on each end. Electrical current flowing through wires generates heat, and when too much current flows through a wire, it can overheat and melt the plastic insulation of the wires, causing short circuits and fires.
This is normally not a problem when you plug an appliance directly into an outlet using its factory cord because the manufacturer has sized the cord appropriately for the electrical current demand, or load, that the appliance requires. But if you use an undersized extension cord to extend the reach of that appliance cord, you can exceed the safe load capacity of the extension cord, and the result can be disastrous.
Extension Cord Gauge and Length
- Wire gauge: The thickness or diameter of the wire affects how much current the wire can carry and how much the wire heats up.
- Length: The length of the extension cord affects voltage drop, or how much voltage is lost through resistance in the cord wires.
Gauge is a numerical rating of copper wire diameter and is identified by an American Wire Gauge (AWG) number. For example, a 12 AWG, 120-volt cord contains 12-gauge wires and is intended for use with standard 120-volt outlets. In the AWG rating system, the smaller the number the thicker the wire.
Voltage drop is an effect that reduces the voltage of electricity in wiring due to electrical resistance. The longer the wire, or cord, the greater the voltage drop. For this reason, long extension cords have a lower capacity than shorter cords of the same AWG size.
For example, an 18 AWG cord may only be rated for 5 to 7 amperes (amps) of load at a length of up to 25 feet. To get the same load rating with a 50-foot cord, the cord must have larger, 16 AWG wire. Because of the voltage drop, it's best to use the shortest extension cord possible for the job at hand.
Light-Duty Extension Cords
Light-duty extension cords are those that resemble lamp wire cord. These cords should never be used with anything other than very light-duty devices. They are especially dangerous to use with space heaters and other heat-generating appliances, such as toasters or clothes irons, which draw heavy electrical loads. Light-duty cords often are not grounded: They have only two plug prongs and do not include a third wire and prong for grounding, so you should never be used with appliances that have a three-prong grounded cord.
- Uses: lamps, clocks, and other light-duty electrical devices drawing up to 7 amps
- Cord length up to 25 feet: use 18 AWG wire
- Cord length up to 50 feet: use 16 AWG wire
- Cord length up to 100 feet: use 14 AWG wire
Medium-Duty Extension Cords
Medium-duty cords usually are grounded extension cords, which include the third wire and plug prong for grounding. They have plugs that accept three-prong grounded appliance cords.
- Uses: televisions, computers, and other devices that draw up to 10 amps of power
- Cord length up to 25 feet: use 16 AWG wire
- Cord length up to 50 feet: use 14 AWG wire
- Cord length up to 100 feet: use 12 AWG wire
Heavy-Duty Extension Cords
Heavy-duty extension cords are suitable for drawing 10 to 15 amps of power. These are always grounded extension cords that include a third wire and plug prong for grounding and have plugs with three slots for accepting grounded appliance cords.
- Uses: tools and heating appliances drawing up to 15 amps of power
- Cord length up to 25 feet: use 14 AWG wire
- Cord length up to 50 feet: use 12 AWG wire
- Cord length up to 100 feet: use 10 AWG wire
Note: Follow appliance manufacturer instructions regarding the use of extension cords. Some appliances never should be used with extension cords.
Built-In GFCI Protection
When using extension cords outdoors, below-grade (such as in a basement or crawlspace), or anywhere a cord might encounter moisture, the cord should be GFCI (ground-fault circuit-interrupter) type or should be plugged into a GFCI-protected outlet. Some extension cords include built-in GFCI protection. This protection helps prevent shock hazards.