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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Jeffery Foster on July 03, 2014, 05:58:10 pm

Title: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Jeffery Foster on July 03, 2014, 05:58:10 pm
If I use, for example, a 45kW generator at an outdoor gig, and choose not to use the GFCI outlets on the included distro, does this place anyone in harm's way?

I believe I've read where sound providers (among others) are *not* required to use GFCI outlets, (when it's reasonably expected that the general public does not have access to the outlets- feel free to correct me if I'm mistaken).  As our amplifiers are more prone to trip GFCI breakers, I'd like to not use them.  But of course, I can't take a chance of somebody potentially being injured.

Thoughts on this?
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Benjamin Gingerich on July 03, 2014, 06:11:29 pm
If I use, for example, a 45kW generator at an outdoor gig, and choose not to use the GFCI outlets on the included distro, does this place anyone in harm's way?

I believe I've read where sound providers (among others) are *not* required to use GFCI outlets, (when it's reasonably expected that the general public does not have access to the outlets- feel free to correct me if I'm mistaken).  As our amplifiers are more prone to trip GFCI breakers, I'd like to not use them.  But of course, I can't take a chance of somebody potentially being injured.

Thoughts on this?
GFCI or not, I believe it's imperative to ground generators, a 6-9ft reusable rod could save evey life around in case of surges, lighting or other disasters. I watched an AC unit blow up on a non-grounded system a few days ago, very scary.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Jeffery Foster on July 03, 2014, 06:19:10 pm
GFCI or not, I believe it's imperative to ground generators, a 6-9ft reusable rod could save evey life around in case of surges, lighting or other disasters. I watched an AC unit blow up on a non-grounded system a few days ago, very scary.

I agree with this.  However, this is much different than the protection that the GFCIs provide, correct?
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 03, 2014, 06:50:52 pm
I agree with this.  However, this is much different than the protection that the GFCIs provide, correct?

I would use GFCIs I do. Sometimes they will shutoff do to a voltage drop somehow but the protection the provide is great. A circuit breaker and a ground rod will NOT stop someone from getting shocked, even if you put a 20amp cuircuit hot leg directly to the ground rod it will NOT tripp the breaker, just make the ground rod, and ground around it hot. at ground rod is for giving a reference/equal potential field

A GFCI on the other hand provides great protection against shock, I use them as much as possible. The check for the current going out and current coming back on the neutral if they are not the same (meaning there is a loss due to some issue or someone getting shocked) it will trip. keep in mind drawing too much current over a lower gauge for or too long of a distance can cause this to trip as well.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 03, 2014, 06:54:29 pm
As our amplifiers are more prone to trip GFCI breakers, I'd like to not use them.

Your amplifiers might have an issue. Is it all of them or a certain model? have you tried plugging them in directly to a gfci individually to see what happens?
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Ray Aberle on July 03, 2014, 08:11:36 pm
Depends on what you're doing and where the outlets are coming from.

- Courtesy outlets on generator: GFCI
- Using 50A twist to spider boxes, where anyone can plug into them? They're GFCI.
- Cam lock from gennie to your distro-- well, the expectation is that the feeder cable from the distro is going to some sort of RackPack in an amp rack, where the public does not have access to the outlets. (The twist lock feeder cabling is also considered something non-accessible to the public.) Do those outlets need GFCI protection? (As far as I know) They do not. However, your "stage stringers," giving backline power to the band SHOULD have GFCI protection on them.

-Ray
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Kevin Graf on July 03, 2014, 08:12:38 pm
GFCIs are not about Fault conditions!  That's what circuit breakers and Safety Ground wires are about.  GFCIs are about enough leakage current to kill you but nowhere near enough current to trip a breaker.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Jeffery Foster on July 03, 2014, 08:16:36 pm
Your amplifiers might have an issue. Is it all of them or a certain model? have you tried plugging them in directly to a gfci individually to see what happens?

All of our amps are QSC.  I honestly haven't conducted a controlled experiment with GFCIs to see if they will always trip them, or only a certain few, or a particular combination.  I should.  I do know that I have tripped a GFCI with them before.  But as we know, these could theoretically be leaking up to 3.5mA and still be UL rated.  Two of them on one circuit would exceed the 6mA required to trip.

That's why I wondered if I could use non-GFCI circuits off the generator yet still be safe.

Thanks for the input!
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 03, 2014, 08:18:39 pm
Depends on what you're doing and where the outlets are coming from.

-Do those outlets need GFCI protection? (As far as I know) They do not. However, your "stage stringers," giving backline power to the band SHOULD have GFCI protection on them.

-Ray

This! for sure this will be where you are most likely to have issues.
Keep in mind if wired properly only the first outlet in your stringers needs to be a GFCI and the rest can be normal spec grade outlets and just pass through the GFCI as ground fault protection for the whole circuit.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Kevin Graf on July 03, 2014, 09:28:06 pm
Experiment with your power conditioners also. Some models dump the noise currentonto the Safety Ground wire which then trips the GFCI. That is the noise current bypasses the GFCI on the return path.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Jeffery Foster on July 03, 2014, 09:40:03 pm
Experiment with your power conditioners also. Some models dump the noise currentonto the Safety Ground wire which then trips the GFCI. That is the noise current bypasses the GFCI on the return path.

I don't use power conditioners for the amp racks.

We do use a UPS on the console and one for the digital snake.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 03, 2014, 09:49:32 pm
Experiment with your power conditioners also. Some models dump the noise currentonto the Safety Ground wire which then trips the GFCI. That is the noise current bypasses the GFCI on the return path.
IMO high current draw devices like power amps shouldn't be on a Powerconditioner. I would only use SurgeX type devices on low power draw electronics (digital snake, wireless racks, FOH mixer, Monitor mixer etc)
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Ron Hebbard on July 04, 2014, 12:35:59 am
I would use GFCIs I do. Sometimes they will shutoff do to a voltage drop somehow but the protection the provide is great. A circuit breaker and a ground rod will NOT stop someone from getting shocked, even if you put a 20amp cuircuit hot leg directly to the ground rod it will NOT tripp the breaker, just make the ground rod, and ground around it hot. at ground rod is for giving a reference/equal potential field

A GFCI on the other hand provides great protection against shock, I use them as much as possible. The check for the current going out and current coming back on the neutral if they are not the same (meaning there is a loss due to some issue or someone getting shocked) it will trip. keep in mind drawing too much current over a lower gauge for or too long of a distance can cause this to trip as well.

Hello again Jason;

From your post quoted above, I'm questioning this portion: 
"even if you put a 20amp cuircuit hot leg directly to the ground rod it will NOT tripp the breaker, just make the ground rod, and ground around it hot."

Here's my understanding of what you're saying:
A given generator is bonded to a ground rod.
(I understand you never said the generator is bonded to the rod, please pardon my assumption.)
If you take a 20 Amp 'hot leg' from this same generator and connect it directly to this same ground rod it won't trip the associated 20 Amp breaker.

Huh?  What?? 
Please explain to me why this dead short won't trip the 20 Amp breaker.
I suppose you could tell me it's a very small generator, capable of only a couple of Watts, incapable of generating enough short circuit current to trip the 20 Amp breaker but I'm doubting this.
You could also tell me the generator wasn't running at the time and I might understand this.

Toodleoo!
Ron
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 04, 2014, 01:00:31 am
Hello again Jason;

From your post quoted above, I'm questioning this portion: 
"even if you put a 20amp cuircuit hot leg directly to the ground rod it will NOT tripp the breaker, just make the ground rod, and ground around it hot."

Here's my understanding of what you're saying:
A given generator is bonded to a ground rod.
(I understand you never said the generator is bonded to the rod, please pardon my assumption.)
If you take a 20 Amp 'hot leg' from this same generator and connect it directly to this same ground rod it won't trip the associated 20 Amp breaker.

Huh?  What?? 
Please explain to me why this dead short won't trip the 20 Amp breaker.
I suppose you could tell me it's a very small generator, capable of only a couple of Watts, incapable of generating enough short circuit current to trip the 20 Amp breaker but I'm doubting this.
You could also tell me the generator wasn't running at the time and I might understand this.

Toodleoo!
Ron

Go try it (not really), I promise you it won't. unless it is a newer breaker that has added this protection or a GFCI breaker.  This is not a short, unless you are calling it a short to ground which is in fact a Ground Fault. A ground rod will only draw 4-5 amps and won't trip the breaker.

If the generator is bonded to the rod it should indeed trip, but unfortunately not everyone drives a ground rod.  also I've seen people use separate ground rodes for stage and generator, this will also create the same issue.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Tim McCulloch on July 04, 2014, 02:43:04 am
Go try it (not really), I promise you it won't. unless it is a newer breaker that has added this protection or a GFCI breaker.  This is not a short, unless you are calling it a short to ground which is in fact a Ground Fault. A ground rod will only draw 4-5 amps and won't trip the breaker.

If the generator is bonded to the rod it should indeed trip, but unfortunately not everyone drives a ground rod.  also I've seen people use separate ground rodes for stage and generator, this will also create the same issue.

Even if the idjits don't drive a rod, the genny neutral should not be floating with reference to EGC ("ground" terminal).  And NEC requires the neutral of the genset to be bonded to the generator frame if it powers loads that are not directly attached to outlets mounted on the genset itself.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: TJ (Tom) Cornish on July 04, 2014, 07:55:19 am
Go try it (not really), I promise you it won't. unless it is a newer breaker that has added this protection or a GFCI breaker.  This is not a short, unless you are calling it a short to ground which is in fact a Ground Fault. A ground rod will only draw 4-5 amps and won't trip the breaker.

If the generator is bonded to the rod it should indeed trip, but unfortunately not everyone drives a ground rod.  also I've seen people use separate ground rodes for stage and generator, this will also create the same issue.
You are conflating bonding (the low-impedance connection from the ground bus to the neutral bus) with grounding (earthing).

If the generator is bonded as it should be (not all are), then absolutely the OCPD will trip.

A ground rod does not "draw" any particular amount of current. A ground rod connects the earth to the electrical system in question; the quality (impedance) of this connection can vary by an order of magnitude or more depending on soil conditions and distance to the other earth fault required to complete the circuit.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Mike Sokol on July 04, 2014, 09:20:55 am
You are conflating bonding (the low-impedance connection from the ground bus to the neutral bus) with grounding (earthing).

If the generator is bonded as it should be (not all are), then absolutely the OCPD will trip.

A ground rod does not "draw" any particular amount of current. A ground rod connects the earth to the electrical system in question; the quality (impedance) of this connection can vary by an order of magnitude or more depending on soil conditions and distance to the other earth fault required to complete the circuit.

That's correct. The two primary reasons for a ground/earth rod are:

1) Keep the voltage of your local "ground plane" (your generator and stage metal along with the chassis of all "grounded" instruments) close to earth potential. Without that "earth" connection your stage and all gear can develop rather high potential above earth when a lightning cloud is overhead. Also, high tension lines over top of your stage can induce thousands of volts (perhaps up to 10,000) but at low amperage (they claim less than 5 mA) which can get you a pretty nasty jolt which the PoCo says won't kill you. I personally think that's a bad thing.

2) Provide a shunting path to earth for any lightning hits in the area. Without that earth grounding path, a nearby lightning strike will cause all sorts of side-flashes between your stage gear and the earth causing lots of damage. 

Bonding the generator neutral to its frame ground provides the fault current return path for when there's a direct line-to-chassis short in a piece of gear, or a wire is pinched in a piece of staging or scaffolding. 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. Do the math... 120 volts divided by 100 ohms equals 1.2 amps which won't trip a current breaker, though it will trip a GFCI.

I'll try to answer the OP's question about where the GFCIs should be placed a little later. I've got to go pick up my musical Tesla coil kit this morning for a STEM class I'm teaching about electricity next week. Yup, 2 ft arcs of musically modulated lightning. I'll post pictures next week.  ;D
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Frank DeWitt on July 04, 2014, 10:10:57 am
I think it was Mike Holt that said Earth is a very good conductor, but it doesn't come with good connectors.  A 5 ft long 5/8 dia rod just doesn't have a whole lot of surface area to make a good enough connection to earth to trip a 20 amp breaker. 
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 04, 2014, 01:36:40 pm

Bonding the generator neutral to its frame ground provides the fault current return path for when there's a direct line-to-chassis short in a piece of gear, or a wire is pinched in a piece of staging or scaffolding. 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. Do the math... 120 volts divided by 100 ohms equals 1.2 amps which won't trip a current breaker, though it will trip a GFCI.

Just curious what would happen in water? or more likely salt water to increase the conductivity of it?
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Mike Sokol on July 04, 2014, 03:30:00 pm
Just curious what would happen in water? or more likely salt water to increase the conductivity of it?

I'm working with a marina guy on this so I know the answer to that question. Salt water (the ocean) provides nearly an ideal "short" to earth, certainly less than 1 ohms with anything the size of a boat. I've seen a test with a 20-amp VariAC feeding the aluminum hull of a boat which would trip the breaker from the current going into the salt water.

On the other hand, fresh water has a much higher resistance, so much so that there's an electric field that will extend out dozens of yards from the boat or dock with electrified metal in the water. The closer you swim to the electrified dock, the more your arms become paralyzed until you eventually sink below the water and drown. Called Shock-Drownings, these normally show up in the autopsy as simple drownings since you weren't really "electrocuted". It's generally assumed that you got tired and stopped swimming even though you were being shocked. So if you're swimming towards a boat or dock with electric power and feel any kind of tingle or tightness in your arms, reverse direction and find another place to swim to a few hundred feet from your original destination.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Lyle Williams on July 04, 2014, 06:27:22 pm
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.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: jasonfinnigan on July 04, 2014, 06:38:03 pm
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.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Stephen Swaffer on July 04, 2014, 10:40:01 pm
 

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.
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Ron Hebbard on July 05, 2014, 12:24:00 am
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
Title: Re: If I don't use a GFCI distro on a genny, where is the ground fault protection?
Post by: Lyle Williams on July 05, 2014, 06:04:00 am
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.