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Author Topic: GFCI Theory  (Read 10476 times)

Mike Sokol

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GFCI Theory
« on: September 20, 2013, 04:41:15 pm »

Here's an article on GFCI theory I just posted on PSW.

http://www.prosoundweb.com/article//no_shock_zone_understanding_and_preventing_electrical_damage_and_worse/

As you can see, GFCIs really don't need a safety ground at all to protect you from electrocution. I'm prepping for a gig tonight, but will add some more info about GFCIs after I get back early next week. In the meantime, please post anything you think is important about GFCI usage in the pro-sound world.
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Jonathan Johnson

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Re: GFCI Theory
« Reply #1 on: September 21, 2013, 01:02:38 am »

Note that GFCI is also abbreviated simply GFI sometimes. Whether the abbreviation is GFCI or GFI, it refers to the exact same thing.

Another common protective device, now required in certain residential circuits in the US (since the 2005 NEC), is an Arc-Fault Circuit Interrupter (AFCI or AFI). This technology detects the waveform distortion caused by electrical arcing and disconnects the circuit.

More information on AFCI here: http://www.afcisafety.org/

"There is a major difference between the functioning of an AFCI as compared to a GFCI (Ground Fault Circuit Interrupter). The function of the GFCI is to protect people from the deadly effects of electric shock that could occur if parts of an electrical appliance or tool become energized due to a ground fault. The function of the AFCI is to protect the branch circuit wiring from dangerous arcing faults that could initiate an electrical fire."
« Last Edit: September 21, 2013, 01:06:05 am by Jonathan Johnson »
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Jonathan Johnson

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Re: GFCI Theory
« Reply #2 on: September 21, 2013, 12:46:25 pm »

The National Electrical Manufacturer's Association (NEMA) has a presentation on GFCI theory, construction, and application:

http://www.nema.org/Products/Pages/GFCI.aspx

This appears to be a slideshow presentation. It would be more meaningful if we had the audio portion, but there's still something to be learned here.
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John Roberts {JR}

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Re: GFCI Theory
« Reply #3 on: September 21, 2013, 01:43:45 pm »

And in Europe they are called RCD (residual current devices)....

JR
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Jonathan Johnson

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Re: GFCI Theory
« Reply #4 on: September 21, 2013, 06:35:31 pm »

And in Europe they are called RCD (residual current devices)....

JR

NEMA claims that GFCI is superior to RCD  ;)
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John Roberts {JR}

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Re: GFCI Theory
« Reply #5 on: September 21, 2013, 09:30:58 pm »

NEMA claims that GFCI is superior to RCD  ;)
It seems like either they work or they don't...

There is always room for improvement, and they probably will.

JR
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Richard Turner

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Re: GFCI Theory
« Reply #6 on: September 24, 2013, 08:33:36 am »


Minimum code reqires all outlets in bedrooms to be attached to arcfault breakers now. A primer on those would also be a good read.
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Tim McCulloch

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Re: GFCI Theory
« Reply #7 on: September 24, 2013, 11:15:04 am »

Minimum code reqires all outlets in bedrooms to be attached to arcfault breakers now. A primer on those would also be a good read.

New home builders in my city were successful in lobbying the City Commission to remove arc flash devices from the local Codes.  The builders claimed that the $200-$300 the devices would add to the cost of a new home would threaten their businesses.

It's up to state, county and/or city to adopt Codes, and the Codes offered by the NFPA are only models, offered for local adoption.
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John Roberts {JR}

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Re: GFCI Theory
« Reply #8 on: September 24, 2013, 01:38:56 pm »

New home builders in my city were successful in lobbying the City Commission to remove arc flash devices from the local Codes.  The builders claimed that the $200-$300 the devices would add to the cost of a new home would threaten their businesses.

It's up to state, county and/or city to adopt Codes, and the Codes offered by the NFPA are only models, offered for local adoption.

I am apprehensive about the added cost and complexity. Will these outlets work flawlessly for several decades?

I kind of like the Euro approach to put RCD in the breaker panel so all outlets on a given branch are protected, while there are complaints about false triggering due to dampness or whatever, the current leakage is probably really happening.  Of course this gets expensive to retrofit.

I have installed a few GFCI to bathroom and kitchen outlets near water and low z ground paths, not sure about utility of retro fitting arc flash for me... ?

JR
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TJ (Tom) Cornish

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Re: GFCI Theory
« Reply #9 on: September 24, 2013, 03:11:33 pm »

I am apprehensive about the added cost and complexity. Will these outlets work flawlessly for several decades?

I kind of like the Euro approach to put RCD in the breaker panel so all outlets on a given branch are protected, while there are complaints about false triggering due to dampness or whatever, the current leakage is probably really happening.  Of course this gets expensive to retrofit.

I have installed a few GFCI to bathroom and kitchen outlets near water and low z ground paths, not sure about utility of retro fitting arc flash for me... ?

JR
As a forced user of arc-fault breakers in my home, I can say that I'm not a fan.  The logic of determining what is an undesirable arc and arcing of brushed motors and normal switch closure arcing is apparently not an exact science.  I am unable to run power tools on arc-fault circuits (I know - not an original design goal, but "remodeling happens", as they say), and every time I spin down my Bridgeport milling machine (powered by a VFD and the mill is by my breaker panels), one of my arc-fault breakers trips if there's a load on that circuit.

I'm sold on GFCI breakers; not so much arc-fault based on personal experience.
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Mike Sokol

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Re: GFCI Theory
« Reply #10 on: September 25, 2013, 08:18:00 am »

I'm sold on GFCI breakers; not so much arc-fault based on personal experience.

I would agree. In a few industry articles I've read, there hasn't been a single documented case of an AFCI actually preventing an electrical fire. The electrical fire started anyways, or the AFCI tripped so often with things like AC/DC motor loads that it was removed. Seems like a good idea that was poorly implemented.

On the other hand, GFCI breakers really do save lives, as long as they're installed properly. A young girl was electrocuted last year at an Orlando miniature golf water feature. The police report stated there were GFCI breakers feeding the fountain pump, but somehow they were installed improperly so they didn't trip.

I've not played with this on the bench, but I'm pretty sure there's a way to improperly install a GFCI breaker so that it will test as OK using the built-in TEST button, but not actually be able to disconnect the circuit during an electrocution incident. More to study on that aspect of GFCIs.
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John Roberts {JR}

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Re: GFCI Theory
« Reply #11 on: September 25, 2013, 10:33:48 am »

The GFCI outlets I recently installed in my house have separate input connections and thru connections, so you can daisy chain to another outlet and protect it. I suspect if the input power is connected to the thru side instead of the input side, the series power disconnect switch may be ineffective.

That's a little scary, since the folks doing electrical wiring are not known for precision in following instructions.

JR

[edit] Just for chuckles I wired up my spare GFCI outlet backwards to see what happens.  If the GFCI is tripped before you wire it up wrong, the reset will not latch while miswired, so the outlet stays cold.  However if the GFCI is cleared by first wiring it up correctly and resetting it, then miswiring it, it passes current from the thru back to the outlet. ::) ::) The manual test button kills it, and it won't reset again, but I suspect this manual test is not the same as a true ground fault so I do not know for a fact that it would offer any protection in this mode of operation. I did not test for response to an actual electrical fault in this mode. This is odd enough that I tested it twice just to be sure I didn't imagine it. Now I am curious about the actual internal connections because when tripped the miswired outlet goes cold... connected backwards the input screws stay cold even before tripping so perhaps more than one pole switch inside? It kind of does what I thought but not how I thought with one pole switch. 

FWIW my outlets came with a yellow warning tape across the thru connections to discourage casual miswiring. The design looks like it "should" prevent miswiring ASSuming that any electrician will press the test button at least once after installing the new GFCI outlet. If miswired it won't reset..   Caveat: this is anecdotal and not all GFCI are the same so YMMV.  [/edit]
« Last Edit: September 25, 2013, 02:05:09 pm by John Roberts {JR} »
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Tim McCulloch

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Re: GFCI Theory
« Reply #12 on: September 25, 2013, 12:15:01 pm »

That's a little scary, since the folks doing electrical wiring are not known for precision in following instructions.

JR

The situations where I was present and others were put a risk due to electrical issues, were at the hands of licensed electricians who thought that colors didn't mean anything and that so long as a device worked when it was plugged in, things were all good...

I think I've mentioned before that I was head electrician when our county's new arena presented their first 3 shows.  The electrical contractor had shirt-and-tie guys as well as technicians present at the first 2 shows, and I got to spend some time with them.  What surprised me was how little they knew about what happens on "our" side of the service disconnect.  I gave them a walk through of how a concert distributes and uses electricity and they, in turn, gave me a tour of the facility's electrical infrastructure.  Great day to be at work :)
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Mike Sokol

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Re: GFCI Theory
« Reply #13 on: September 26, 2013, 08:40:54 am »

Tim,

I like the Nuclear Apathy - Crack The Sky lyrics quote in your tag. I'm guessing not a lot of others know this "Crack" reference. Crack the Sky was (is?) a sorta local Baltimore band that I've seen a number of times. I saw them open for Frank Zappa at the B'more Civics center in the late 70's. Zappa sat out front and applauded the entire time they were on stage.  8)
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Mike Sokol
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Tim McCulloch

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Re: GFCI Theory
« Reply #14 on: September 26, 2013, 11:15:56 am »

Tim,

I like the Nuclear Apathy - Crack The Sky lyrics quote in your tag. I'm guessing not a lot of others know this "Crack" reference. Crack the Sky was (is?) a sorta local Baltimore band that I've seen a number of times. I saw them open for Frank Zappa at the B'more Civics center in the late 70's. Zappa sat out front and applauded the entire time they were on stage.  8)

You caught me, Mike.  Actually I've been a CtS addict from their second album... and I think they still play a show at the Reicher every couple of years.  Maybe one of these days I'll be there...

"From the moon we're comedy, from the moon we're really quite a treat."
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Mike Sokol

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Re: GFCI Theory
« Reply #15 on: September 26, 2013, 02:36:45 pm »

Here's an update on an industrial 3-phase GFCI with variable threshold settings. http://tinyurl.com/o29zt8u

As you can see, it's a 3-phase unit with up to 100 Amp capability. From a quick read it appears to be for line-to-line loads only (motors and heaters?), not for line-to-neutral loads as we would normally use to power our amps and stage gear. And it's selectable for 6, 10, 20 and 30 mA trip points, but not while in GFCI mode since that's a code violation, or something to that effect. Should be an interesting read though.

I'm guessing that at some future point the lighting industry will probably require this sort of thing, but I don't believe that's of immediate concern. But it's always good to look ahead a little to see what's coming down the pike...
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Jeff Robinson

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Re: GFCI Theory
« Reply #16 on: September 28, 2013, 12:50:28 am »

Here's an update on an industrial 3-phase GFCI with variable threshold settings. http://tinyurl.com/o29zt8u

As you can see, it's a 3-phase unit with up to 100 Amp capability. From a quick read it appears to be for line-to-line loads only (motors and heaters?), not for line-to-neutral loads as we would normally use to power our amps and stage gear. And it's selectable for 6, 10, 20 and 30 mA trip points, but not while in GFCI mode since that's a code violation, or something to that effect. Should be an interesting read though.

I'm guessing that at some future point the lighting industry will probably require this sort of thing, but I don't believe that's of immediate concern. But it's always good to look ahead a little to see what's coming down the pike...

http://www.trci.net/products/hd-pro/6-10-30-60a-80a

A company that's been doing it for 30 years. Founded to build military genset controls.

There are applications at 480 (+) volts that can establish arcs that do not grow large enough to trip OCD's. Also required for all (un-shielded) pipe heat tracing (30mA is standard for this).

5mA trip level is required to be called GFCI for people protection. ELCI is for equipment protection.

Many industrial UL489 breakers offer a ground fault option (the G in LSIG).

Full disclosure: I've sold their devices a few times in the last 15 years.

HTH,

Jeff Robinson
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Canute J. Chiverton

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Re: GFCI Theory
« Reply #17 on: October 15, 2013, 07:02:26 pm »

Is it true that the inline GFCI sometimes falsely trip and therefore can shut off power?  Is this a regular occurrence?
« Last Edit: October 16, 2013, 01:19:56 am by Canute J. Chiverton »
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David J. Thomas

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Re: GFCI Theory
« Reply #18 on: October 15, 2013, 08:00:19 pm »

Effectively they work the same way.  They both sense unwanted current to ground and shut power off, however, a GFCI (by commonly accepted US standards) must shut power off when it senses current leakage of 6mA maximum, whereas an ELCI can be set to shut off power at almost any current leakage level.
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John Chiara

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Re: GFCI Theory
« Reply #19 on: October 15, 2013, 08:17:10 pm »

I would agree. In a few industry articles I've read, there hasn't been a single documented case of an AFCI actually preventing an electrical fire. The electrical fire started anyways, or the AFCI tripped so often with things like AC/DC motor loads that it was removed. Seems like a good idea that was poorly implemented.

On the other hand, GFCI breakers really do save lives, as long as they're installed properly. A young girl was electrocuted last year at an Orlando miniature golf water feature. The police report stated there were GFCI breakers feeding the fountain pump, but somehow they were installed improperly so they didn't trip.

I've not played with this on the bench, but I'm pretty sure there's a way to improperly install a GFCI breaker so that it will test as OK using the built-in TEST button, but not actually be able to disconnect the circuit during an electrocution incident. More to study on that aspect of GFCIs.

That girl was a friend of mine's neice. Still waiting on the lawsuit on that one.
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Mike Sokol

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Re: GFCI Theory
« Reply #20 on: October 25, 2013, 04:25:53 pm »

That girl was a friend of mine's niece. Still waiting on the lawsuit on that one.
If you have or can get any information on how the GFCI was miswired in this tragedy, I would love to see it. PM me with details to keep it offline since I'm sure the lawyers don't want this sort of info disseminated on a public forum. 
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