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Author Topic: Bonding and false positive tests on GFCI  (Read 21267 times)

Stephen Swaffer

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Bonding and false positive tests on GFCI
« on: August 31, 2014, 12:11:52 pm »

Since we were headed OT and somewhat irrelevant to the OPs post, I started a new thread, but I want to comment on Guy's staement.

"The false positive generated by GFCI test circuits on ungrounded Floating Neutral generators does nothing to eliminate faulty equipment and only creates a false sense of security."

First, it has been discussed in depth on other threads here that just because a generator is built without a bonded neutral/ground does not make it OK to use it like that if code does not allow it for the purpose.  The places that an unbonded neutral is allowed are limited-and there are ways to bond the neutral.

Secondly, I understand the argument behind your statement; however, what is the purpose for a GFCI?  Simply to prevent electrocuting someone.  If I place myself between a hot and a neutral no GFCI will ever trip period.  If I place myself between a hot and ground-but there is no path back to the neutral (a VERY iffy proposition) then I will not be harmed -GFCI in circuit or not.  However, IF there is enough of a path (inadvertent or intentional) to allow a harmful 5 mA to travel through my body and return to the circuit bypassing the GFCI then a GFCI will in fact protect me with or with out a neutral "bond".

The correct way is to follow code and if you are using a genny to supply audio gear for a gig, make sure you bond the neutral and ground. And make sure that neutrals and grounds are separated in any distros/gear that you use.
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Steve Swaffer

frank kayser

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Re: Bonding and false positive tests on GFCI
« Reply #1 on: August 31, 2014, 01:10:58 pm »

Since we were headed OT and somewhat irrelevant to the OPs post, I started a new thread, but I want to comment on Guy's staement.

"The false positive generated by GFCI test circuits on ungrounded Floating Neutral generators does nothing to eliminate faulty equipment and only creates a false sense of security."

First, it has been discussed in depth on other threads here that just because a generator is built without a bonded neutral/ground does not make it OK to use it like that if code does not allow it for the purpose.  The places that an unbonded neutral is allowed are limited-and there are ways to bond the neutral.

Secondly, I understand the argument behind your statement; however, what is the purpose for a GFCI?  Simply to prevent electrocuting someone.  If I place myself between a hot and a neutral no GFCI will ever trip period.  If I place myself between a hot and ground-but there is no path back to the neutral (a VERY iffy proposition) then I will not be harmed -GFCI in circuit or not.  However, IF there is enough of a path (inadvertent or intentional) to allow a harmful 5 mA to travel through my body and return to the circuit bypassing the GFCI then a GFCI will in fact protect me with or with out a neutral "bond".

The correct way is to follow code and if you are using a genny to supply audio gear for a gig, make sure you bond the neutral and ground. And make sure that neutrals and grounds are separated in any distros/gear that you use.
The problem I see is that generators are sold consumer-off-the-shelf (COTS) to end users that have no idea about code or situations where they should or should not be used.  I know my Honda EU1000 specifically states not to drive a ground rod and has no mention of whether it is a floating or bonded ground.  In ways, it seems that including too much information may be seen as the manufacturer as an additional point of liability.  The "plug it in, and if you don't understand that, get an electrician" mindset works for and against them.
I don't think Honda had it in mind that their EU gennies would be powering audio rigs - though their use seem a natural to us.  Honda does have their EB series gennies with GFCI and bonded ground, which probably would be more suitable... 

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Stephen Swaffer

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Re: Bonding and false positive tests on GFCI
« Reply #2 on: August 31, 2014, 06:14:10 pm »

The "plug it in, and if you don't understand that, get an electrician" mindset works for and against them. 

Arguably a reasonable position to take for the average consumer.  I don't consider sound/lighting providers the "average consumer."  When you provide a service to the public, you are take on responsibility for "the public's" safety.

As an electrician, there are a dozen or more trades-from operating heavy equipment, to welding, structural design, rigging, etc. that I need to know the basics of and be able to handle simple things as well as know when to call an expert.  IMO grounding is a basic safety consideration that anyone setting up sound gigs with either shore or genny power needs to thoroughly understand ( this forum is an excellent tool to accomplish that) so they can get it right-or know they need to call an expert "this" time.

Grounding is not as sexy or fun as setting up a bunch of gee whiz effects processors, amps, subs etc but it is just as necessary as driving to the gig.
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Steve Swaffer

Jeff Bankston

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Re: Bonding and false positive tests on GFCI
« Reply #3 on: August 31, 2014, 07:09:45 pm »

in los angeles any generator thats built on a set of wheels has to be connected to a ground rod. even all of our contruction site gens had to have a permit from la building and safety and a ground rod driven at the gen. the electrical inspector would come and inspect before we were allowed to use it. a friend runs gens for tv/movie shoots , i will ask him what is required for his 18 wheeler gen rig.
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Mike Sokol

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Re: Bonding and false positive tests on GFCI
« Reply #4 on: August 31, 2014, 09:36:27 pm »

in los angeles any generator thats built on a set of wheels has to be connected to a ground rod.

And I'm guessing the generator must also have its neutral bonded to this "earth ground". Any requirements for metal stages to be bonded to this same generator "ground"? 
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Mike Sokol
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Jeff Bankston

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Re: Bonding and false positive tests on GFCI
« Reply #5 on: September 01, 2014, 03:53:49 am »

And I'm guessing the generator must also have its neutral bonded to this "earth ground". Any requirements for metal stages to be bonded to this same generator "ground"?
i bond steel frame of the wood deck trailer to the disto panel ground which is connected to the generator ground. metal steps are bonded to the trailer.
« Last Edit: September 01, 2014, 04:00:16 am by Jeff Harrell »
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Guy Holt

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Re: Bonding and false positive tests on GFCI
« Reply #6 on: September 01, 2014, 08:03:20 pm »

... a friend runs gens for tv/movie shoots , i will ask him what is required for his 18 wheeler gen rig.

Unless something changed very recently, it was my understanding from my West Coast IA brothers that the preferred practice in Los Angeles was to not earth ground generators, but rather completely insulate them from earth as stipulated in this excerpt of the safety guidelines established by the Safety Committee of the Contract Service Administration Trust Fund (CSATF), an industry wide administrative body (governed by the collective bargaining agreement by and between the Producers, The International Alliance of Theatrical Stage Employees ("I.A.T.S.E."), the Moving Picture Technicians Artists and Allied Crafts of the United States, its Territories, and Canada ("M.P.T.A.A.C."); as well as the collective bargaining agreements by and between the Producers and the Basic Crafts Locals (Article 18))..

“Generators mounted on trucks or trailers shall be completely insulated from earth by means of rubber tires, rubber mats around metal stairways and rubber mats under any type of lift gate or jacking device. Metal supports for trailers shall be insulated by means of wooden blocks. Safety tow chains shall be secured so as to not touch the ground. If complete insulation is not possible, a grounding electrode system shall be installed per the National Electrical Code, Article 250.52.”

Guy Holt, New England Studio Mechanics/IATSE Local 481 Certified Gaffer
ScreenLight & Grip
rentals@screenlightandgrip.com
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Stephen Swaffer

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Re: Bonding and false positive tests on GFCI
« Reply #7 on: September 02, 2014, 01:13:25 am »

I question the wisdom of this preferred method.

First, it would seem to require at least as much effort as providing a good earth ground.

Second, all the careful isolation can be undone with just one careless placement of any metallic tool, stand what have you or even somebody leaning against the trailer .  Maybe in a tightly controlled studio lot (though I am not usually that trusting of coworkers when it comes to my safety)-but very iffy in a venue with public access.

Though LA is probably a drier environment than I am used to so perhaps less susceptible to accidental grounds and harder to get a good ground?
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Steve Swaffer

Jonathan Johnson

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Re: Bonding and false positive tests on GFCI
« Reply #8 on: September 02, 2014, 01:18:44 am »

OK, this doesn't make sense to me.

If a generator has a floating neutral (not bonded to ground/frame of genny), then what's the point of a GFI that's factory-installed in the generator? A short to ground will never result in a complete circuit back to neutral upstream of the GFI, so it will never trip. In order for it to trip in the event of a downstream fault, there would have to be a fault WITHIN the generator itself, that creates an unintentional upstream bond between the generator circuitry and the frame.

What am I misunderstanding here? The whole idea of the GFI is that it detects current bypassing the GFI. And if there is no bond upstream, there can be no current bypassing the GFI.
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Jeff Bankston

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Re: Bonding and false positive tests on GFCI
« Reply #9 on: September 02, 2014, 01:31:32 am »

Unless something changed very recently, it was my understanding from my West Coast IA brothers that the preferred practice in Los Angeles was to not earth ground generators, but rather completely insulate them from earth as stipulated in this excerpt of the safety guidelines established by the Safety Committee of the Contract Service Administration Trust Fund (CSATF), an industry wide administrative body (governed by the collective bargaining agreement by and between the Producers, The International Alliance of Theatrical Stage Employees ("I.A.T.S.E."), the Moving Picture Technicians Artists and Allied Crafts of the United States, its Territories, and Canada ("M.P.T.A.A.C."); as well as the collective bargaining agreements by and between the Producers and the Basic Crafts Locals (Article 18))..

“Generators mounted on trucks or trailers shall be completely insulated from earth by means of rubber tires, rubber mats around metal stairways and rubber mats under any type of lift gate or jacking device. Metal supports for trailers shall be insulated by means of wooden blocks. Safety tow chains shall be secured so as to not touch the ground. If complete insulation is not possible, a grounding electrode system shall be installed per the National Electrical Code, Article 250.52.”

Guy Holt, New England Studio Mechanics/IATSE Local 481 Certified Gaffer
ScreenLight & Grip
rentals@screenlightandgrip.com
i dont know what the motion picture/la la palooza type events/tv shows do about grounding but when i or anyone else goes to rent a gen on axles we "must" have a gen pernit from the city of los angles. if we dont have a permit we are not allowed to rent a gen. once we have the permit the rental company delivers the gen. an electrical inspector comes before the event to make sure an 8' ground rod is driven next to the gen and a proper size ground wire is attatched. he also makes sure the gen isnt parked ubder a tree as i have ben told happens. if the stage is metal or has metal parts he checks that for grounding wires. after he signs off then and only then can i turn the gen on and power stuff up. the city of los angeles might have different rules for union crews but we are just a band doing our own stuff with my pa. we only play in daylight so no lights are used. i havent ben able to talk to my union friend that runs the big stuff cause he is on a production set working 12hr days right now.

also a friend bought 3 new MQ axle mounted gens about 18 months ago. we started using his 80KW gen and he wont let me hook my truck to it if i dont have a permit.
« Last Edit: September 02, 2014, 01:36:39 am by Jeff Harrell »
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ProSoundWeb Community

Re: Bonding and false positive tests on GFCI
« Reply #9 on: September 02, 2014, 01:31:32 am »


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