On 10/14/2013 7:39 PM, Mike Marlow wrote:
dpb wrote:
On 10/14/2013 6:50 PM, Bill Leonhardt wrote:
In my shop I have two general purpose electrical circuits that I
connect everything to except the big machines. They are 20 amp
(120VAC)circuits with 12 gauge wire. Each circuit starts with a GFCI
outlet and then a chain of normal outlets. All outlets are 20 amp.



GFCIs work on the current imbalance between the two legs and trip as
low as 5-6 mA. What this indicates is that the motor now has a
leakage path that ends up being above the GFCI threshold--it probably
started off at just barely under and know with some age there's some
insulation degradation that has let it now be just over instead of
just under.

Or it indicates an aging GFCI. These things do not have long life
expectancies.

I'd find that more convincing if it weren't both failing at the same
exact time...that's just _too_ coincidental...

Your choices as I see it are--

a) replace the GFCI w/ a different/newer one and see if goes away for
at least a while,

That would be my first approach.

It's certainly the simplest...


b) replace the motor w/ one that doesn't have the leakage current. It's
highly unlikely you'll be able to change its characteristics any
although despite no heavy dust buildup you might try blowing it out
thoroughly w/ compressed air to see if internal dust could be
contributing to the problem, or

I find this one to be less likely.

Well, in the days of GFCIs originally motors were notoriously
high-enough leakage to cause them to trip. That a presumably
Chinese-motor on an import tool has enough after a few years to now
cause a trip (on two separate ones, no less) is less remarkable
occurrence to me than the two GFCIs failing identically.

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