Choosing the Right Extension Cord: Amperage, Size, and Safety

Extension cords extend a home's or workshop's electrical circuits when a lamp, appliance, or tool has an attached cord that is too short to reach the needed location. Most people have several extension cords they keep on hand for this purpose. What is often not considered, though, is that these extension cords need to be of an appropriate size for the power load being placed on them.

Read on to learn more about extension cord amps, wattage, and safety considerations when using them.

How Extension Cords Work

An extension cord extends a short power cord to reach a power outlet and transfer power from the outlet to the device. They come in many lengths, from 2 feet to 100 feet. Connecting two extension cords is not recommended because it can cause a drop in amperage.

An extension cord has three parts: the socket (female), the cord, and the plug (male). The socket is where you plug the wire from a device or appliance; the cord carries the current, and the plug goes into a wall outlet. The thicker the cord, the more electrical current it can safely carry.

Ensure a three-prong plug goes to a three-pronged power outlet. A two-prong plug is OK to connect to a three-prong outlet.

Extension Cord Ratings

Extension cords vary in rating based on the amperage they can safely carry and the wattage they can handle—both of which are determined by the gauge of the wire. The amperage rating for each extension cord should be labeled on a tag attached to each cord, but this label may not always be present or visible. 

When choosing an extension cord, it's essential to determine the amount of wattage and amperage drawn by the tool or appliance connected to it. The familiar basic household extension cord is acceptable in most cases with simple devices, such as lamps, radios, televisions, and other electronics. These basic extension cords usually use 16-gauge wire.

Things get more complicated when you use an extension cord for devices with motors or when they produce heat. The electrical load of these items is substantially higher, which means lightweight extension cords should not be used with them. 

When using longer extension cords, electrical current resistance is higher, and the potential for overheating is greater. A 5-foot-long heavy-duty extension cord powering a table saw rarely overheats, but a 50-foot-long extension cord of the same wire gauge may well be undersized for the job. 

Matching Extension Cord to Load

Extension cords should be rated for loads that are at least equal to and preferably greater than the requirements needed to run a tool effectively. Based on the chart below, extension cord lengths of 50 feet or less can be used, but runs over 50 feet should implement the next heavier-sized cord to accommodate voltage drop due to the natural resistance of the wire.

Colors do not indicate how much power they can transfer. They are more used for aesthetics. Bright yellow or orange cords are usually thicker gauges in heavy-duty situations, such as construction work sites. Black or white cords are commonly used in homes, blending in with other electric cords.

Safety Reminder

Discard or repair extension cords that are missing ground connections, show signs of extreme wear, or have cracks or cuts, or if you can see bare wire exposed through the outer jacket of the cord. Cords without ground connections can be dangerous to the user. Nicks and bare exposed wires can cause electrical shock.

Also, examine the plug ends on your extension cords for damage. Your local hardware store has replacement plugs that can extend an extension cord's life, provided the cord is in good condition.

Never use extension cords with space heaters. Due to their high wattage and amperage demands, numerous house fires have occurred when heaters are plugged into extension cords. Instead, space heaters should be plugged directly into electrical outlets. Ensure you do not exceed the circuit's amperage rating. If you find that a circuit breaker trips or a fuse blows when you plug in a space heater, try another circuit with heavier wire and a larger circuit breaker amp rating.