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Recently I installed some 15A GFCI outlets in my basement to make using power tools more convenient, but quickly had problems with them tripping on my miter saw. This seemed extra odd since my miter saw doesn't even have a ground wire.

I found lots of help online about how to test these and table saws with ohm meters to look for shorts, but none of those explained my problem, especially once I realized I had been using it for years on an outlet that was also GFCI protected. I figured I should post my solution now that I figured it out.

  • Is it a variable speed saw? – DJohnM Sep 19 '16 at 18:36
  • Is it connected to an extension cable? If not, what's the condition of the plug cable? If it is, what's the gauge and length of the cable? – Chris Sep 19 '16 at 18:47
  • My saw is single speed. It worked correctly with and without a heavy extension cord in good condition on different 20A GFCI outlets. It failed with and without the same extension cord on different 15A GFCI outlets. I think my neighbor's saw is also single speed. He used a beat up extension cord that may not even have a ground pin in both the successful 20A test and unsuccessful 15A test. – Seth Sep 19 '16 at 19:26
  • What is the power rating of the miter saw? – ratchet freak Sep 20 '16 at 10:46
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I tested my miter saw on a 20A GFCI outlet, it worked fine. I tested my neighbors miter saw on a second 20A GFCI outlet on a second circuit in my house, it also worked fine. But after plugging my miter saw into the 2 indoor 15A GFCI outlets, it would trip the GFCI the moment I started the saw. My neighbor reported a similar problem when he plugged his miter saw into my outdoor 15A GFCI outlet.

So, while it could have been a short, and tripping a GFCI is often evidence that there is something (dangerously) wrong with your power tool, for me the solution was to replace the 15A GFCI outlets with 20A GFCI outlets (on a 20A circuit). Both saws are working fine now.

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Most miter and table saws are high amperage draws, some even exceeding 15amps. Sounds like you are overdrawing the circuit. That's why they work in your neighbors 20a receptacles. I would replace the receptacles with 20amp receptacles and make sure you have 12-2 wiring.

  • That wouldn't trip a GFCI receptacle though -- GFCI receptacles are differential trip only, not the combined OC/SC/Diff (ground fault) protection provided by a GFCI breaker – ThreePhaseEel Sep 20 '16 at 4:02
  • That's what everything I read online said, too. But replacing the receptacles cured the problem. – Seth Oct 4 '16 at 14:00

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