gfci tripping when I switch bath fan off

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Brian G

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san jose,ca,u.s.a
I have a bath fan that i put in a shower, so i put it on the load side of gfci. Sometimes when you turn the fan off it tripps the gfci. It never tripps it when you turn it on only when you turn it off. I cant figure out why this is happening, any thoughts?
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130420-0042 EDT

In a long past post I commented on this. I was able to simulate the the problem with an inductive load.

This results from the inductive kick from turning off an inductor with current flowing.

Looking at the GFCI circuit layout I could see one likely cause. It is not of any great concern to me so I did not try a change in the GFCI circuit to see if the probability could be reduced.

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kwired

kwired

Electron manager
Location
NE Nebraska
Inductive kick back, throw away your cheap GFCI and install a reputable one - they are designed to withstand this problem.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130420-1122 EDT

kwired:

Specify the brands you classify as reputable. Also what in particular in these designs eliminates or reduces the probability of false tripping?

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kwired

kwired

Electron manager
Location
NE Nebraska
gar said:
130420-1122 EDT

kwired:

Specify the brands you classify as reputable. Also what in particular in these designs eliminates or reduces the probability of false tripping?

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Click to expand...

Anything that normally sells for less than $8.00 - $10.00 is likely unacceptable. Maybe withstand was the wrong word to use, I should have said reputable devices will (and are designed to) tolerate more inductive kickback before tripping, they still will suffer from this problem at times, but not from a typical shaded pole motor used in a bath fan.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
130420-1524 EDT

kwire:

The test I had run several years ago was on a Leviton and I generally considered the design to be reasonably good and very good in some ways. But I could cause false tripping from the load side and not the input side with a fairly good inductive load, an 8 ft dual Slimline. This easily can produce 3000 to 4000 V transients.

It was hard to cause the Leviton to trip, but it should not have. I never tried to modify the GFCI to see if I could reduce its sensitivity, but it just had too long a lead to the SCR gate.

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kwired

kwired

Electron manager
Location
NE Nebraska
A few years ago when we had wide spread power outages due to ice storm, I was running the house on a portable generator (through a manual transfer switch). One time when the generator ran out of fuel, I heard the generator sputter a bit, knew it was likely running out of fuel, then as it quit I heard a pop come from various locations throughout the house. Every one of my P&S GFCI receptacles had tripped. Probably some inductive kickback going on there I would guess. But I have had very few issues of tripping these receptacles. Did try an occupancy sensor switch in bathroom in my shop one time, was supplying T8 electronic ballasted luminaire. It would trip a GFCI receptacle in the area that was on same circuit but the load in question was not connected to the load side of this GFCI. Would not trip every time, but did trip quite frequently. I don't know why it only tripped when using that occupancy sensor, same light had been there a long time with no issues and no issues after going back to a standard switch. - Again a P&S GFCI. Have had very few cases otherwise where the trip reason was unknown.
 
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