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How can extension cords become dangerous?
Thursday, July 12, 2018
Although extension cords are not hazardous when utilized within the limitations of their design, they are only meant for short-term use and most have a small wire size that has limited current-carrying capacity. But extension cords often get used for what is essentially permanent wiring, and multiple appliances and lights connected to one cord may exceed its safety rating. The 18-gauge copper wires in a typical household extension cord, like the one shown above, are rated for a maximum of 10 amps; but any small portable electric space heater, for example, draws 15 amps. The next larger size, 16-gauge, also falls short at a 13-amp rating.
Here’s four situations where an extension cord becomes a safety hazard:
1) An extension cord that is run under a carpet or behind the headboard of a bed will become frayed over time. Arcing at the frayed wires can start a fire.
Because a household extension cord is not rated for the 20-amps of the circuit breakers protecting many wall outlets today, multiple appliances and lights plugged into a single extension cord will overheat the wires and can start a fire without the breaker ever tripping.
When an electrical cable is permanently installed, it is required to be protected from damage within conduit or in the wall cavity. But an extension cord left in place for years is subject to being rolled over, walked on, tripped over, and impacted by dropped objects. Long-term sunlight exposure will also deteriorate the cord sheathing. Damaged extension cords can cause arcing and a short circuit.
Because most household extension cords are two-wire and do not have a ground wire, connecting an appliance cord that has a ground prong necessary for shock protection (by pulling out the ground prong or using a “cheater” plug connector) will eliminate the shock protection.
We define a permanently installed cord as one that is connected to an appliance that stays in one place and is used regularly. So an extension cord plugged in to use a leaf blower in the yard is temporary, but one that runs from a wall outlet in the garage to the ceiling for a garage door opener is permanent. Extension cords that run around the perimeter of a room which has only one wall outlet in an older house is another example of a permanent installation.
One way to tell if a home has an inadequate number of wall outlets is to look for extension cords running around the room and peeking out at the baseboard between furniture pieces. Pre-1950 homes often have only one receptacle per bedroom and none in the dining room, and outlets that are 2-slot ungrounded; so we often see multiple cords attached to power bars that are plugged into the wall with ground prong removed, or with cheater plugs, in older homes—like in the photo below, where the heavy cord running up to the top of the picture goes to a power bar with more stuff plugged into it. This particular old-time Gainesville home also still had the original knob-and-tube wiring running to the receptacles, which was not designed to carry these electrical loads.
The National Fire Protection Association (NFPA) has published standards for “Electrical Inspections of Existing Buildings,” also known as NFPA-73, which has the following guidelines for how NOT to use extension cords—which they refer to as flexible cords and cables:
- They should not be used as a substitute for permanent wiring.
- Not extended through holes in walls, ceilings, or floors.
- Not run through doors, windows, or under carpets.
- And not attached to building surfaces.
- The NFPA further specifies that any offending cords should be removed and, where necessary, replaced with permanent wiring.
One final note: a damaged extension cord should be thrown away, not repaired. “Repaired” extension cords are a prime fire hazard.
Also, see our blog posts What does over-fused mean? and Can I run an electric power cord or extension cord through the wall?
To learn more about electrical wiring, devices, and receptacles, see these other blog posts:
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