Sizing Extension Cords to Fit the Length of the Run

Extension cords are a convenient way to extend electrical circuits to areas where outlets are not readily available. However, it is important to consider the length of the run when using extension cords. Tying multiple extension cords together may not provide enough power to operate tools and can also be unsafe. How can you determine the appropriate number of extension cords to use for a given project?

Other factors to consider include the distance of the outlet from the circuit breaker panel, the size of the circuit breaker and wiring feeding the outlet, and the size of the extension cord.

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Voltage Drop

Frequently, users neglect to match the extension cord size to the length of the run and instead use a variety of sizes. However, longer runs of wire encounter resistance, which can cause heat damage not only to the cord but also to connected power tools. The voltage drop caused by this resistance can overheat the motors of the tools.

If you have ever damaged a drill by using it in an improper manner as described above, you should be aware of what to avoid in the future. If a tool runs slower than usual when powered, this is a sign of voltage drop and should prompt you to stop and prevent damage to the tool. Using a heavy-duty extension cord or cords can often address this issue. It is important to avoid using undersized extension cords for long runs and powering heavy-load equipment such as sump pumps and compressors.

Two hands with Extension Cords want to Plug Each Other in White Background.
Baby FSN / Abrar Khan

Extension Cord Usage Chart

Length (Feet)Maximum AmperageWire Guage
Extension Cord Usage Chart

Why It Matters

The longer the wire run, the more resistance and heat are generated. This can affect power tools by not allowing them to function correctly and efficiently. The electrical load may be too much for the size of the extension cord. Choosing the right extension cord is important, a heavy gauge wire should be chosen, by following the provided chart. The chart shows the maximum amperage and wire gauge that can supply over a certain number of feet. As more feet are added to the cord, the amperage availability decreases.

Voltage drop in the cord can prevent power tools from running at full speed, leading to overheating and damage to the tool’s wiring and contacts. As the tools overheat, so do the extension cords they are connected to, which can cause circuit breakers to trip due to overheating or overloading of the circuit.

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