GFCI vs Variable Speed DC Motor

Mike907 · Post by **Mike907** » Sat Mar 15, 2014 5:22 pm

The supplement to the PowerPro manual says that the PowerPro will trip a GFCI receptacle. I plug my PowerPro into one and it has never tripped.

I have a new Jet mini lathe with a variable speed DC motor, and it trips the same outlet every time the speed is increased to about 2/3 max.

I kind of like the idea of ground fault protection, so does anyone know of gfci outlets that can handle the DC motor, or will I just have to install a non-gfci outlet?

Thanks,

Mike

wa2crk · Post by **wa2crk** » Sat Mar 15, 2014 6:07 pm

Mike
I also have the Delta variable speed mini lathe and I have it in a GFCI receptacle and I have never tripped the GFI with the PP or the lathe. Do you have the 46-460 type one or two? I think that there were changes to the type two that corrected the problems. Try changing the breaker with "Made in the USA " hospital grade GFCI.
Bill V
PS you may try to tie some overhend knots in the power cord to add some inductance which may block some of the RF getting on the power cord.

Mike907 · Post by **Mike907** » Sat Mar 15, 2014 10:38 pm

Thanks, Bill

The lathe is a Jet 1221VS.

Shopsmith says that the PowerPro won't trip a GFCI breaker, but will a GFCI receptacle. I have a receptacle, but the PowerPro seems to work fine. I'll look into the hospital grade version, but in the meantime, the overhead receptacle that the garage door plugs into seems to not be gfci, and the lathe works fine there.

Thanks again,

Mike

charlese · Post by **charlese** » Sun Mar 16, 2014 12:25 pm

I cured my GFCI outlet problem by purchasing and installing a hospital grade GFCI outlet. I believe I was the first to point this out to Shopsmith, as they had never heard of the issue before. I was told that the shop at Shopsmith has all GFCI breakers - no special outlets.

Anyway, went to an electrical supplier store locally, after searching the internet, and requested the hospital type outlet. It solved the problem.

JPG · Post by **JPG** » Sun Mar 16, 2014 3:04 pm

charlese wrote:I cured my GFCI outlet problem by purchasing and installing a hospital grade GFCI outlet. I believe I was the first to point this out to Shopsmith, as they had never heard of the issue before. I was told that the shop at Shopsmith has all GFCI breakers - no special outlets.

Anyway, went to an electrical supplier store locally, after searching the internet, and requested the hospital type outlet. It solved the problem.

Do you know why a hospital grade receptacle is less prone the false gfci tripping with the power pro? AIUI the difference has to do with anti-tampering and plug retention.

charlese · Post by **charlese** » Sun Mar 16, 2014 4:52 pm

JPG40504 wrote:Do you know why a hospital grade receptacle is less prone the false gfci tripping with the power pro? AIUI the difference has to do with anti-tampering and plug retention.

No! All I know is the change worked:) Purely empirical.

JPG · Post by **JPG** » Sun Mar 16, 2014 10:18 pm

charlese wrote:No! All I know is the change worked:) Purely empirical.

Wonder if it is a class 'B' which has a higher leakage current trip point.

Never mind, class B is not relevant to hospital receptacles.

JPG · Post by **JPG** » Sun Mar 16, 2014 10:48 pm

GFCI in a hospital setting is a mixed blessing. Surely protecting patients and personnel is important, but they have a history of 'nuisance' tripping. I cannot think of a place that nuisance tripping is more of a hazard than the leakage current. Nuisance tripping in a hospital would turn off life support equipment.

So I wonder if Chuck's hospital grade receptacle is less prone to tripping due to spurious leakage current.

BuckeyeDennis · Post by **BuckeyeDennis** » Sun Mar 16, 2014 10:49 pm

JPG40504 wrote:Do you know why a hospital grade receptacle is less prone the false gfci tripping with the power pro? AIUI the difference has to do with anti-tampering and plug retention.

I found a bit of info in a Levitron hospital-grade datasheet. It claimed improved immunity to nuisance tripping from high-frequency noise. And then I found a the same claim from Levitron on a NON-hospital grade GFCI.

I can personally attest that switching transients from motor drives, in conjunction with noise-suppression filters incorporating line-to-ground capacitors, will trip some GFCI's. To combat this, I once went so far as to specify an isolation transformer between the AC supply and some motor drives from a major manufacturer.

A true ground fault would result in 60Hz ground current. Motor drive noise is usually at least 8 kHz, with most of the energy way up in the higher harmonics.

Apparently, higher-quality GFCI's do a better job of ignoring the high-frequency stuff. It stands to reason that hospital-grade GFCI's need to be better. You don't want your ventilator shutting off for no good reason!

JPG · Post by **JPG** » Sun Mar 16, 2014 11:11 pm

BuckeyeDennis wrote:I found a bit of info in a Levitron hospital-grade datasheet. It claimed improved immunity to nuisance tripping from high-frequency noise. And then I found a the same claim from Levitron on a NON-hospital grade GFCI.

I can personally attest that switching transients from motor drives, in conjunction with noise-suppression filters incorporating line-to-ground capacitors, will trip some GFCI's. To combat this, I once went so far as to specify an isolation transformer between the AC supply and some motor drives from a major manufacturer.

A true ground fault would result in 60Hz ground current. Motor drive noise is usually at least 8 kHz, with most of the energy way up in the higher harmonics.

Apparently, higher-quality GFCI's do a better job of ignoring the high-frequency stuff. It stands to reason that hospital-grade GFCI's need to be better. You don't want your ventilator shutting off for no good reason!

Way back when I was gainfully employed, every hour on the hour GFCIs tripped all over the place.

It was determined that the self correcting clocks were the cause. These clocks were designed to run slightly slow, and a signal was superimposed on the power line to trigger a self set to '0' minutes each hour change. This higher frequency signal was causing greater leakage current than the normal 60 Hz frequency.

I ran frequency tests on the GFCIs in use there and determined that at the clock signal frequency, the GFCIs tripped at less than 2 ma.

I forwarded that to the squareD plant down the road. They thought I was nuts! But then they did not have IBM/Simplex clocks! Not sure they realized the significance. I have to assume they were even more sensitive at higher frequencies.

That was a few decades back when GFCI were 'new'.