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Author Topic: GFCI Theory  (Read 10491 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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