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Author Topic: If I don't use a GFCI distro on a genny, where is the ground fault protection?  (Read 5857 times)

Jeffery Foster

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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.
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jasonfinnigan

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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)
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Ron Hebbard

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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
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jasonfinnigan

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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.
« Last Edit: July 04, 2014, 01:51:11 am by JasonFinnigan »
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Tim McCulloch

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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.
« Last Edit: July 04, 2014, 10:41:28 am by Tim McCulloch »
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TJ (Tom) Cornish

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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.
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Mike Sokol

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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
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Mike Sokol
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Frank DeWitt

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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. 
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jasonfinnigan

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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?
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Mike Sokol

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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.
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Mike Sokol
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