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Old 02-23-2008, 03:13 PM   #16
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Sub Panel Grounding Question.


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Originally Posted by InPhase277 View Post
That means static, lightning, and high voltage line crossings. The Earth is not the path for fault current at line voltage.

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Article 250.4(A)(5)
Effective ground Fault Current Path
"Electrical equipment, wiring and other conductive materials likely to become energized shall be installed in a manner that creater a permant low impedance circuit capable of safely carrying the maximum ground fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source."

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Old 02-23-2008, 03:18 PM   #17
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Sub Panel Grounding Question.


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Originally Posted by wire_twister View Post
Article 250.4(A)(5)
Effective ground Fault Current Path
"Electrical equipment, wiring and other conductive materials likely to become energized shall be installed in a manner that creater a permant low impedance circuit capable of safely carrying the maximum ground fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source."
Are you saying a ground rod clears a fault? I really hope your not...
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Old 02-23-2008, 03:25 PM   #18
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Sub Panel Grounding Question.


not at all, the first post I made was in response to Speedy Peatys comment that a ground rod did not provide a ground, did not prevent you from getting a shock, did not have anything to do with causing a circuit breaker to function.
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Old 02-23-2008, 03:28 PM   #19
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Sub Panel Grounding Question.


Quote:
Originally Posted by wire_twister View Post
Article 250.4(A)(5)
Effective ground Fault Current Path
"Electrical equipment, wiring and other conductive materials likely to become energized shall be installed in a manner that creater a permant low impedance circuit capable of safely carrying the maximum ground fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source."
Right, this is not the same as "effectively grounded". The ground fault path is not through the Earth. The impedance of dirt is way too high to carry enough current to operate an overcurrent device.

If you actually believe that short circuit current goes to the Earth, then you are in the wrong business my friend. We call it "grounded", but it has nothing to do with the Earth. There are two circuits you have to think of. One circuit is for taking fault current back to the main bonding jumper at the service. This is accomplished by a bare or green wire, and is the circuit you mention in the quote above.

The other circuit is the one from a cloud to the actual Earth. This circuit is the one lightning needs to complete it's journey. This is why we stick a rod in the dirt.

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Old 02-23-2008, 03:31 PM   #20
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Sub Panel Grounding Question.


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Originally Posted by wire_twister View Post
not at all, the first post I made was in response to Speedy Peatys comment that a ground rod did not provide a ground, did not prevent you from getting a shock, did not have anything to do with causing a circuit breaker to function.
The only fault a ground rod clears is that 50,000 amp pulse that God sends down your service during a thunderstorm.

And it has NOTHING whatsoever to do with causing a circuit breaker to function. None, zip, zilch, zero, nada.

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Old 02-23-2008, 03:34 PM   #21
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Sub Panel Grounding Question.


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Originally Posted by InPhase277 View Post
The only fault a ground rod clears is that 50,000 amp pulse that God sends down your service during a thunderstorm.

And it has NOTHING whatsoever to do with causing a circuit breaker to function. None, zip, zilch, zero, nada.

InPhase277

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Old 02-23-2008, 03:34 PM   #22
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Sub Panel Grounding Question.


Quote:
Originally Posted by wire_twister View Post
Article 250.4(A)(5)
Effective ground Fault Current Path
"Electrical equipment, wiring and other conductive materials likely to become energized shall be installed in a manner that creater a permant low impedance circuit capable of safely carrying the maximum ground fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source."
the source is the transformer that feeds the service, not the ground. That ground conductor and the low impedance path has 0 to do with the "earth" ground we provide for several reasons, most of which were covered by others.
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Old 02-23-2008, 03:37 PM   #23
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Sub Panel Grounding Question.


So all these ground rods, loops, plates, and other electrodes are solely for protection from static, lightning or sources other than line voltage? Is this what you are saying?
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Old 02-23-2008, 03:41 PM   #24
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Sub Panel Grounding Question.


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Originally Posted by wire_twister View Post
So all these ground rods, loops, plates, and other electrodes are solely for protection from static, lightning or sources other than line voltage? Is this what you are saying?
What did you think they did? Check out 250.4 (A)(1)

Last edited by chris75; 02-23-2008 at 03:43 PM.
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Old 02-23-2008, 03:44 PM   #25
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Sub Panel Grounding Question.


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What planet are you on??
OBVIOUSLY not the same planet as you junior.

Thanks folks for the answers. I was out shopping with the family.
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Answers based on the 2008 & 2011 NEC.
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Old 02-23-2008, 03:53 PM   #26
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Sub Panel Grounding Question.


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well, how about this to throw a little fun in the works.

a ground rod is NEVER mandatory. Period.

Petey? I know you know what I am stating here.
This is one of the things that is good about a Ufer.
If there is plastic water pipe feeding a house, under the 2005/2008 NEC a Ufer is the ONLY required grounding electrode.
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Old 02-23-2008, 04:22 PM   #27
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Sub Panel Grounding Question.


If I may chime in for a sec... I want to make sure I have this right.


The groundED conductor (neural) is required for a circuit to be complete, so the electrons (?) can take the path of least resistance to their origin, which would be the center tap of the transformer.

The groundING (bare/green) conductor's primary function is to carry fault current back to the main panel/disconnect where the bonding jumper is so it can continue on the path of least resistance to through the service neutral back to the center tap of the transformer.

When there is a ground fault, yes the ground wire WILL carry the current back to a place where it meets up with the service neutral, then will continue down the service neutral thus NEVER even coming close to the grounding electrode (water, rod, ufer, etc).

Am I correct?

When there is a lightning strike, WHY will it go to earth instead of through the service neutral?
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Old 02-23-2008, 04:28 PM   #28
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Sub Panel Grounding Question.


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When there is a lightning strike, WHY will it go to earth instead of through the service neutral?
it probably will since the transformer has a ground rod as well, but what your really trying to do is prevent surface arching...
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Old 02-23-2008, 04:31 PM   #29
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Sub Panel Grounding Question.


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Originally Posted by CowboyAndy View Post
If I may chime in for a sec... I want to make sure I have this right.


The groundED conductor (neural) is required for a circuit to be complete, so the electrons (?) can take the path of least resistance to their origin, which would be the center tap of the transformer.

The groundING (bare/green) conductor's primary function is to carry fault current back to the main panel/disconnect where the bonding jumper is so it can continue on the path of least resistance to through the service neutral back to the center tap of the transformer.

When there is a ground fault, yes the ground wire WILL carry the current back to a place where it meets up with the service neutral, then will continue down the service neutral thus NEVER even coming close to the grounding electrode (water, rod, ufer, etc).

Am I correct?
Absolutely.

Quote:
When there is a lightning strike, WHY will it go to earth instead of through the service neutral?
Some of the current will go back on the service neutral, and then to the Earth ground at the transformer. But having an Earth ground at the service keeps the path that the strike has to travel to complete it's circuit as short as possible. You want the lightning current to get to the Earth through as short a path as possible. The longer it stays in your wiring, the greater the chance that it will find other paths to jump off too. For example, you might see it arc from your fridge to your sink!

If lightning is striking near your house, that means the difference in potential that is driving the current is between the cloud and the Earth near your house. You want to have your Earth ground near there too. Does that make sense?

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Old 02-23-2008, 04:46 PM   #30
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Sub Panel Grounding Question.


There is no restaurant in the ground where the electrons want to go to. They want to return to the source, and may use the ground (earth) to get there.

One of my early instructors taught us that.

If you connect a jumper cable to the positive post of your car battery, and throw the other end in a mud puddle, no current will flow. If you drive a ground rod and connect it to the negative terminal on the battery, current will flow, limited by the resistance of the earth.

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