Now as I've previously mentioned I'm new on here and I LOVE asking questions:grin: ...............a friend of mine who works in selling industrial assembly systems asked me if I was aware of an issue of have 2 GFCIs together. I asked what he meant and he said that in his garage the circuit is GFCI protected and when he plugs a fastening controller into it which has an internal GFCI it trips his garage GFCI circuit everytime, but when he plugs it into a normal 120V circuit that isn't GFCI protected it works fine.
2 GFCI Cause Issue?
- Thread starter awc
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- Massachusetts
awc said:
It sounds like your friends controller has a problem.
You can connect as many GFCIs in a row as you want, they do not effect each other.
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pbeasley
Senior Member
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- Orange County, CA (for now)
but they can certainly effect you when trying to get them all reset :grin:iwire said:
mdshunk
Senior Member
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- Right here.
It's more likely if you had 10 connected in series, only the weakest or most sensitive one will trip.pbeasley said:
Hello again fellas.....well i've spoke to other people within my friends company and this is a common issue with these controllers.........could it possibly have something to do with the electronics within these controllers? The controllers run electric assembly tools that utilize current measurement to give a torque value the tool is tightening to:-? :-? .
- Location
- Wisconsin
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- PE (Retired) - Power Systems
awc said:
GFCI's are not affected by any harmonic current (emi/rfi is a different matter). If the GFCI is tripping the device is leaking current to ground.
L
Lxnxjxhx
Guest
a fastening controller
a fastening controller
Run leakage tests on it or post a schematic if you can.
If the upstream GF devices take several seconds to trip the leakage current might be as low as ~4 mA.
If the controller is double insulated with no ground connection anywhere then you need an Exorcist.
a fastening controller
Run leakage tests on it or post a schematic if you can.
If the upstream GF devices take several seconds to trip the leakage current might be as low as ~4 mA.
If the controller is double insulated with no ground connection anywhere then you need an Exorcist.
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
080423-1829 EST USA
The "fastening controller" may have a low pass noise filter at its input. Quite likely does. This might include one or more capacitors from line(s) to to the chassis and then to the ground pin on the plug. These capacitors provide a leakage path to ground.
The internal GFCI might follow the line filter (be between the filter and the electronics), or it may have a different sensitivity.
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The "fastening controller" may have a low pass noise filter at its input. Quite likely does. This might include one or more capacitors from line(s) to to the chassis and then to the ground pin on the plug. These capacitors provide a leakage path to ground.
The internal GFCI might follow the line filter (be between the filter and the electronics), or it may have a different sensitivity.
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Ok, I ended up going to my friends house and did a little investigating and I believe I've figured out what was going on. First off it definitely bleeds off current to ground, when I removed all paths for ground from the controller which included removing the ground pin off the plug (which was an old cord and we threw it out when done with the testing) it doesn't trip thus the current must be going back on the grounded conductor since that's the only route for it. Another thing I discovered is that I know a typical GFCI trips at a 10milliamp difference in current but the GFCI in the controler trips at 30milliamp thus explaing why the GFCI outlet trips everytime over the one in the controller. So that is where i'm at to this point. As mentioned i'm a newbie but why would it bleed off to ground???
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
080426-0642 EST
awc:
I think your experimental results confirm my suggestion that the "fastening controller" has an input filter. If you have a Fluke DVM you should be able to measure AC MA leaking thru the grounding pin.
For a sample circuit diagram see
http://www.cor.com/Series/PowerLine/B/
This particular model does not have a large leakage current. But that specification will be for 60 Hz. Your "fastening controller" will have much higher frequency components and these will produce higher leakage currents because capacitive reactance is inversely proportional to frequency.
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awc:
I think your experimental results confirm my suggestion that the "fastening controller" has an input filter. If you have a Fluke DVM you should be able to measure AC MA leaking thru the grounding pin.
For a sample circuit diagram see
http://www.cor.com/Series/PowerLine/B/
This particular model does not have a large leakage current. But that specification will be for 60 Hz. Your "fastening controller" will have much higher frequency components and these will produce higher leakage currents because capacitive reactance is inversely proportional to frequency.
.
- Location
- Illinois
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- retired electrician
The GFCI trips at ~5mA, not ten. A 30mA trip device is not a GFCI, it is a ground fault protective device. What type of equipment is using the 30mA GFP device?awc said:
brian john
Senior Member
- Location
- Leesburg, VA
Jim: Assuming a high harmonic content load would there not be a possibility of more leakage current with the high order harmonics?
don_resqcapt19 said:
Don, sorry about that i'm not sure where I got ten from??
I see what you're saying, makes sense. The equipment is a fastening controller that measures torque and angle through current measurement from an attached electric tool. I'll get some further info and post it for everyone to see what i've been talking about. The controller itself has the 30mA GFP device installed on it. Thank you for your help, it appears I need to study this GFP a little bit so i'm 100% on the right page. Thanks again!
cadpoint
Senior Member
- Location
- Durham, NC
awc said:
I think you stated your own answer to your problem, I think its internal to the machine.
My next thought would be that the power is also dual tapped internally, and due to that causes the MA leakage, and your tool is probably double insulated.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080427-1920 EST
Torque controlled drivers are most likely to use a brushless servo because this provides high torque in a given package size compared to a brush type motor.
In either case a filtered DC supply, meaning a bridge rectifier followed by a capacitor input filter, is the likely source for the motor.
A rectifier charging a capacitor draws current at the peak of the AC input voltage for a short time. This creates a large harmonic content in the current drawn from the AC line. To reduce this noise a low pass input filter may be employed at the input to the bridge rectifier. Previously I referenced the Corcom site to illustrate a typical circuit diagram of a filter. This is how you could get high frequency ground currents.
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Torque controlled drivers are most likely to use a brushless servo because this provides high torque in a given package size compared to a brush type motor.
In either case a filtered DC supply, meaning a bridge rectifier followed by a capacitor input filter, is the likely source for the motor.
A rectifier charging a capacitor draws current at the peak of the AC input voltage for a short time. This creates a large harmonic content in the current drawn from the AC line. To reduce this noise a low pass input filter may be employed at the input to the bridge rectifier. Previously I referenced the Corcom site to illustrate a typical circuit diagram of a filter. This is how you could get high frequency ground currents.
.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
brian john said:
In what scenarios would high harmonics cause more leakage current in a single phase 2-wire circuit?
But even if they did, it is the leakage current not the harmonics that is causing the trip which is the proper action.
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
080427-2055 EST
jim dungar:
For a voltage of a given amplitude as you increase the frequency the current thru a capacitor of fixed value will increase, Xc = 1/(2*Pi*f*C). Or for a fixed current amplitude as frequency is increased there is less opposition to current flow. Obviously a function of the load imedance the capacitor sees.
For a given average DC output current from a capacitor input filter the peak input current is much greater than the average ouput current, but short in duration. Maybe 10 times or more. Change to an inductive input filter so that current flows the entire cycle and the input RMS current is quite close to the average DC output current, and thus the peak input current is much lower and of a low frequency than for the capacitor input filter.
Beyond this are currents generated from the switching power supplies driving the motor.
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jim dungar:
For a voltage of a given amplitude as you increase the frequency the current thru a capacitor of fixed value will increase, Xc = 1/(2*Pi*f*C). Or for a fixed current amplitude as frequency is increased there is less opposition to current flow. Obviously a function of the load imedance the capacitor sees.
For a given average DC output current from a capacitor input filter the peak input current is much greater than the average ouput current, but short in duration. Maybe 10 times or more. Change to an inductive input filter so that current flows the entire cycle and the input RMS current is quite close to the average DC output current, and thus the peak input current is much lower and of a low frequency than for the capacitor input filter.
Beyond this are currents generated from the switching power supplies driving the motor.
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