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I have an old 1950s bandsaw (Beaver 2300) that has been refitted with a new motor. It runs fine. But now that I am using a power bar with a built in GFCI, the GFCI trips under heavy load. When I plug directly into the wall outlet, the 15A breaker does not trip.

Any suggestions on why this should occur, or how I should explore this problem?

Thanks in advance.

  • Does it only trip on heavy load? or does it trip as soon as you power the bandsaw on? Do you have any other high drain devices (like a tablesaw or a big DC) you could test the power strip with? – Dave Smylie Jul 31 '17 at 23:43
  • It only trips with a heavy load. I do not have another heavy load device, but I do have another GFCI power bar. I will try it and see. I have used it without the GFCI previously, with no ill effect. Maybe I just got lucky. – Fed Aug 1 '17 at 2:02
  • You may want to check your power strip, as some are actually rated for less than 15A. Also keep in mind that continuous loads should only be 80% of the maximum rated current. – rob Aug 9 '17 at 4:24
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This could indicate a shock hazard, so do be careful while you're diagnosing the problem. In particular, if the motor windings were leaking current to ground (the motor casing and by extension the saw itself), a properly functioning GFCI could exhibit this behavior. Especially avoid touching a metal surface saw while some other part of your body is grounded. Safer yet, avoid using the saw until you have this figured out.

You would need other tests with test equipment to tell, but trying with another GFCI might be an accessible option.

One possible scenario is that the motor windings heat up under load and cracks or other weak spots in the insulation then allow current to flow to ground without passing through the Neutral wire.

Depending on the motor type, it could also be leakage in the run capacitor, an insulation breakdown in the switch, or in any part of the wiring (especially suspect given its age), but a systematic diagnosis here is the best bet. Such a diagnosis would require understanding the electrical principles involved and may be best left to an expert.

I suppose you could eliminate certain whole sections of components by, say, wiring the motor directly to a plug. If that fixed it, the switch and wiring would be suspect; if it still happened, it narrows it down to the motor.

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  • I will try another GFCI power bar. I have used it before several times, with heavy load, with no ill effect, but perhaps I was not grounded. The motor is new, and set up by the prior owner. I will check the wiring carefully. The wiring is new as well. Then I will try to wire the motor directly to the plug and get back to you here. Any further suggestions? I assume that as long as I use the GFCI bar I should be safe, correct? Also, the guy I bought it from used it in this configuration for 2 years without issues. – Fed Aug 1 '17 at 2:09
  • @Fed After a quick search, it appears that "nuisance" trips on GFCIs are a fairly frequent occurrence with motor loads. So it could be there's nothing wrong with the saw at all. Unfortunately, there doesn't seem to be any clear information out there on how to remedy this, although if there's no evidence of current leakage (e.g. you get a shock when you touch the saw when it's turned on) you might consider running it without a GFCI or getting one specifically made for motor loads. – scanny Aug 1 '17 at 3:20

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