Here is a quick tip if you hate dealing with a tangled extension cord any time you try to do yard work with an electric tool: make yourself a cord reel.
We had an old garden hose reel which was being unused so I fed the female end of a 100' long extension cord through the reel's axle and wound the rest of the cord up. When the time comes to use our electric weed eater, it is simply a matter of unwinding the amount of cord we need. And the best part? When the job is finished all you have to do is reel the extension cord back in. That's it! No more extension cord tangle.
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