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Author Topic: If I don't use a GFCI distro on a genny, where is the ground fault protection?  (Read 5854 times)

Lyle Williams

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Are their higher mA rating GFCI's available in the US?  5mA (?) seems a very low threshold.  In Australia regular GFCI/RCD units are 30mA.
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jasonfinnigan

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Are their higher mA rating GFCI's available in the US?  5mA (?) seems a very low threshold.  In Australia regular GFCI/RCD units are 30mA.
No 5ma is right be for the "let go" thresehold for getting shocked (which if you can't let go will eventually kill you). 30ma is well above the 10ma to kill someone seems like that more about protecting gear than people. I'm more worried about people getting hurt than gear IMO.
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Stephen Swaffer

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The ground/earth rod has sufficiently high impedance (25 to 100 ohms and still be code compliant) that it won't trip a 20-amp breaker if there's a line-to-earth short.

Mike knows this, but this is why it is VERY important for anything that we think should be grounded -stages, roofs, equipment racks, generator frames, etc, etc must be connected together with an appropriately sized EGC.  That EGC is connected to a grounding electrode though a GEC.  Then in ONE place the neutral is bonded to the GEC.  That provides a solid metallic path for any fault currents.  The NEC  specifically prohibits using the earth for a ground fault return path.  I guess I don't understand why it seems to be so confusing that anything that might become energized must be able to trace a metallic path back to a ground electrode (rod) AND to the neutral buss of the genny/service. This is a major safety issue-but really really simple if you draw a picture.

GFCIs that have a higher than 5 mA threshold are available but they are not intended or appropriate for personnel protection.
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Steve Swaffer

Ron Hebbard

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Mike knows this, but this is why it is VERY important for anything that we think should be grounded -stages, roofs, equipment racks, generator frames, etc, etc must be connected together with an appropriately sized EGC.  That EGC is connected to a grounding electrode though a GEC.  Then in ONE place the neutral is bonded to the GEC.  That provides a solid metallic path for any fault currents.  The NEC  specifically prohibits using the earth for a ground fault return path.  I guess I don't understand why it seems to be so confusing that anything that might become energized must be able to trace a metallic path back to a ground electrode (rod) AND to the neutral buss of the genny/service. This is a major safety issue-but really really simple if you draw a picture.

GFCIs that have a higher than 5 mA threshold are available but they are not intended or appropriate for personnel protection.


Stephen;

I'm fully in agreement with you and adding a little history.

Decades ago, late seventies / early eighties perhaps, the hot new item in audio / recording / broadcast equipment grounding was 'magic', chemically enhanced, 'special' ground rods for the exclusive use of audio electronics.  A company developed these, advertised them fairly heavily, had them reviewed by all the 'right' people in all the 'right' magazines and soon they were in consultant's spec's.

They became 'must have' / 'all the rage' items.

Folks would cut a hole in their basement floor slab, sink their 'magic rod' into undisturbed soil, regularly anoint it with more 'magic wetting potion' and run anything from 4/0 to 500 MCM insulated, fine-strand, copper to their gear as its ONLY ground conductor.  Sometimes the 'magic rod' was one floor below the equipment, other times it was in the basement with the gear 30 flights up a high-rise tower.

It wasn't too long before there were arcs and shocks between 'magic grounds' vs. building steel, the building's normal electrical grounds and other peoples' 'magic grounds'; I'm sure you have no trouble understanding why.

In my area it's basically you can have as many ground rods as you like, and wherever you want them, but they all MUST, eventually, be bonded to the copper bus running around the perimeter of the building's main hydro room.  Park a generator, or three, in the loading dock to supplement a film shoot?  No problem so long as the generators' grounds are bonded onto the building's one and only common ground system.

One building, one ground. 
One for all and all for one. 
(End of message.)  (This!  (As Tim would say.))

One 'magic' installation in my area featured four 'magic rods' forming the corners of a roughly 10' square in the basement, all bonded to each other and then on to become the only ground on a dedicated breaker panel exclusively for the sound system. 
Some years later, when science caught up with what the 'magic' chemicals could do to your health, the city purchased two hazmat suits of the day and several IA brothers were paid well to dig up all of the hazardous materials then seal them in 'safe' containers for high-dollar disposal.  In this instance, the rods were in a low-ceilinged crawl space below the Neve console in the centre of the main floor of the city's largest road-house.  The lads charged with the removal didn't have much fun hunched over digging in their sealed suits for several days.

Thanks for the memories and keep up the good fight for better, safer, grounding accompanied by comprehensive, universal, understanding.

Toodleoo!
Ron Hebbard
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Lyle Williams

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No 5ma is right be for the "let go" thresehold for getting shocked (which if you can't let go will eventually kill you). 30ma is well above the 10ma to kill someone seems like that more about protecting gear than people. I'm more worried about people getting hurt than gear IMO.

" let go " won't be an issue if the GFCI/RCD trips promptly.  Down here 30mA is the standard for personal protection.  I have heard a range of figures for fatal current, but it is unclear to me whether these are left-hand-to-right-hand currents or currents directly applied to the heart.

30mA GFCI/RCD have been very successful in improving electrical safety in Australia.
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