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Extension Cord Safety

When it comes to electrical safety, there is nothing more common when it comes to danger than the overuse of the humble electrical extension cord. These devices are extremely useful, extending the range of tools and electrical equipment without needing additional infrastructure. Unfortunately, most homes abuse extension cords without regard to their physical limits and the dangers that a few feet of improperly used extensions can create.

Heat Transfer Coefficient

Most people who use an extension cord check a few things. They make sure that there isn’t any exposed wiring and that the cord itself is long enough to reach across the room. And that’s where the safety assurances end. The problem is that many physical properties of extension cords are invisible to people who don’t know to look for them.

The gage of a wire (or thickness or diameter of the wire) determines how easily it conducts electricity. You see, all wiring in a home has a small amount of electrical resistance. As electrical current pushes through the wire, it releases heat in the form of used power.

Here you run into two problems:

  • As the length of extension cord, and the number of devices in use increases, the amount of heat generated and power used increases. When that power use increases above a certain amount, your breaker will trip.
  • On a more dangerous note, as the wire increases in temperature, it can get hot enough to melt plastic or ignite items with a low incendiary point.

This happens because of a strange property of resistance and wiring known as the heat transfer coefficient. You see, as a wire or electrical device heats up, the wire become more resistive. The resistance increases so the power demands for the entire circuit increases. This can eventually reach a run-away state where the wire heats up uncontrollably, demanding more and more power. Usually a circuit breaker will trip, but you run the risk of starting a fire due to the excessive heat generated by the extension cords. Using a lower (thicker) gage or a shorter extension cord helps mitigate this risk. But it’s best to avoid using an extension cord if at all possible.

When and How to Use an Extension Cord

Extension cords are temporary measures for simple tasks. They are never meant to be permanent installations and they are not meant to help power high-load devices for extended periods of time. When using an extension cord, you should never:

  • Nail, staple, or pin the cord to surfaces (you could damage the insulation)
  • Use a cord that feels hot or is damaged
  • Remove the grounding pin from a plug
  • Use an indoor extension cord outside
  • Block walkways or high traffic routes

When using an extension cord you should always:

  • Use the shortest cord possible
  • Inspect all cords for damage before use
  • Insert plugs fully into sockets
  • Ensure that your extension cord has been certified by a testing laboratory (UL, CSA, or ETL)
  • Avoid pinch points, tripping hazards, and taut cables

Every year there are over 4,000 injuries and more than 3,000 home fires all as a result of improper extension cord use. Don’t let yourself become a statistic, be cautious when using an electrical extension cord.