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Author Topic: GFCI leakage testing  (Read 10648 times)

Mike Sokol

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GFCI leakage testing
« on: June 05, 2014, 01:35:34 pm »

Eric says his gear works "everywhere" else-does that include other venues with GFCIs or not?  If the same gear, hooked up the same way trips one GFCI but not another I would suspect a bad GFCI-though the ba d one could be the one that does not trip!  On the other hand, if they have a bad GFCI. you'd think they would have other complaints and would hopefully have found the problem.

The first thing to realize is that ALL gear plugged into an electrical outlet has a certain amount of allowed leakage to its chassis and ultimately ground. For "ungrounded" appliances such as your iPhone charger, there can be a max of 0.75 mA of leakage and still meet UL standards. For "grounded" appliances such as your mixing console, backline gear and power amps, hot-to-chassis leakage can be as much as 3.5 mA and still meet UL approval.   

Secondly, these leakage currents are additive, so it's possible to plug two pieces of audio gear with 3 mA of leakage each into a single GFCI and cause it to trip. As previously mentioned, "Surge Strips" are a big source of MOV leakage, so plugging two of them into a common GFCI circuit can cause a trip, even of each MOV strip is technically in compliance. And old tube guitar amps develop a lot of power transformer leakage which can easily cause a GFCI to trip.

So what to do? Well this may be the time to begin measuring hot-to-chassis leakage currents of your own gear. Most of it will probably be around 1 mA or so, and that implies that 6 pieces on the same GFCI will cause a trip. Of course, anything with 4 or 5 mA leakage by itself is going to cause a second piece of gear to reach the threshold and trip.

For a primer on GFCI theory see here: http://www.noshockzone.org/rv-electrical-safety-part-viii-gfci/

And here's something I wrote about GFCI troubleshooting: http://www.noshockzone.org/rv-electrical-safety-part-x-%E2%80%93-gfci-troubleshooting/

As GFCIs show up at more venues, we're going to need to confirm our own gear leakage. If not, then we'll be stuck with random tripping that makes nobody happy.
 
« Last Edit: June 05, 2014, 01:45:14 pm by Mike Sokol »
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Mike Sokol
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Mike Sokol

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Re: GFCI leakage testing
« Reply #1 on: June 05, 2014, 02:14:04 pm »

FYI: I'm going to ask Klein Tools to send me a demo Klein CL2000 clamp meter for a ground leakage demonstration I'm planning. They also make a CL1000 clamp meter which costs around $100 and has 0.1 mA resolution (according to their literature). So I'll also ask them to send a couple CL1000 clamp meters I can send to a few of you on the forum willing to do some ground-leakage experiments with audio gear and report back to the group. Yes, you'll have to send them back to me eventually, but I'm trying to develop a simple field leakage test that will explain and help eliminate random GFCI tripping on stages. If I can find a few participants on the forum and Klein agrees to the loaner gear, then we'll all learn a little something about why these GFCI trips occur and what we can do about it.

PM me if you want to be part of this test. See http://www.kleintools.com/catalog/clamp-meters/400a-ac-clamp-meter for the meter specs.
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Kevin Graf

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Re: GFCI leakage testing
« Reply #2 on: June 05, 2014, 02:22:17 pm »

Also remember that many so called 'power conditioners' dump the noise to the Safety Ground.
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Mike Sokol

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Re: GFCI leakage testing
« Reply #3 on: June 05, 2014, 02:38:00 pm »

Also remember that many so called 'power conditioners' dump the noise to the Safety Ground.

Yup, they are not a friend to GFCIs.
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Stephen Swaffer

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Re: GFCI leakage testing
« Reply #4 on: June 05, 2014, 08:09:58 pm »

Mike, not to rain on your parade, but you may be disappointed with the results.  I picked up a Klein CL2000 a few months ago, and would highly recommend it for anyone doing audio work  Very versatile, built in NCV the whole works-if I had to take only one of my meters to a job or gig this would be the one.

That said, experience has taught me to disregard fractional amps on most meters and  suspected it was a transducer limitation more than anything.  I put my CL2000 on a rock solid amp draw lighting circuit this afternoon, ,and I could consistently get a variation of 200 mA just by moving the wire in the jaws.

If you check out the Klein manual, my observation is in line with the 40 amp AC range specs.  The low amp range is much more accurate-but it also requires inserting the meter into the circuit via test leads.
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Mike Sokol

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Re: GFCI leakage testing
« Reply #5 on: June 05, 2014, 08:26:13 pm »

Mike, not to rain on your parade, but you may be disappointed with the results.  I picked up a Klein CL2000 a few months ago, and would highly recommend it for anyone doing audio work  Very versatile, built in NCV the whole works-if I had to take only one of my meters to a job or gig this would be the one.

That said, experience has taught me to disregard fractional amps on most meters and  suspected it was a transducer limitation more than anything.  I put my CL2000 on a rock solid amp draw lighting circuit this afternoon, ,and I could consistently get a variation of 200 mA just by moving the wire in the jaws.

If you check out the Klein manual, my observation is in line with the 40 amp AC range specs.  The low amp range is much more accurate-but it also requires inserting the meter into the circuit via test leads.

It will be interesting to find out how repeatable the milli-amp range turns out to be on these inexpensive clamp meters. The Fluke meter and external ammeter clamp I pictured earlier is too expensive for field work, about $1,000 or so. Of course, a lot of digital voltmeters have a 10 amp current range, which may be what's required for this test. However, I really don't want to break the EGC on a test power cable if possible. It would be better if this was a completely benign test, but we shall see how it all works out. I'll talk to Klein engineering to see what they think.
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Stephen Swaffer

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Re: GFCI leakage testing
« Reply #6 on: June 05, 2014, 09:44:47 pm »

Its my understanding that the mA range only functions as wired, not with the clamp-but I haven't had a chance to experiment.  It does sound like an interesting experiment-maybe I need t become a professor so I have time to experiment!

The other way to run a test would be to make a test jig with a low resistance precision resistor in the EGC, then use a mV range to measure the voltage across the resistor and derive the current from that measurement.  Really the same thing, but perhaps less chance of a variation in connection resistance form test to test.
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Mike Sokol

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Re: GFCI leakage testing
« Reply #7 on: June 05, 2014, 10:10:07 pm »

It does sound like an interesting experiment-maybe I need to become a professor so I have time to experiment!

Hey, I've been running electrical experiments since I was 6 years old. I didn't become a professor for another 45 years or so.  ;D
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Mike Sokol
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Mike Sokol

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Re: GFCI leakage testing
« Reply #8 on: June 05, 2014, 10:36:16 pm »

The other way to run a test would be to make a test jig with a low resistance precision resistor in the EGC, then use a mV range to measure the voltage across the resistor and derive the current from that measurement. 

There's a much easier way. If you create multiple loops in the ground wire to clamp the meter through, you'll make a current multiplier. So just 10 loops would increase the resolution of a standard 10 mA minimum clamp meter to 1 mA. Cost would be next to nothing and this would allow everyone to use their existing clamp meters for the leakage test.

Any thoughts?
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Kevin Graf

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Re: GFCI leakage testing
« Reply #9 on: June 06, 2014, 09:34:42 am »

Any thoughts?

a] Many DMM have AC Current ranges.  My 30+ year old bench meter has a 200 uA full scale range, my Radio Shack DMM may go even lower.  So you loop the wire through the DMM and the clamp ohmmeter at the same time.

b] Trying to make accurate reading using the AC power line has it's frustrations.  First the line voltage bounces all around, second the high frequency noise may be read differently with different meters.  So instead of the AC line, use a big power amplifier.  Use a music player with a 60 Hz sine wave signal.  It will be safer and more accurate.
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Speedskater

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Re: GFCI leakage testing
« Reply #9 on: June 06, 2014, 09:34:42 am »


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