Residential ground

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jim123 said:
If a dwelling has metal water pipe coming into a house am I required to use it or can I just drive to two ground rods 6' apart
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I would use the proper term of grounding electrode, the word "ground" is too ambiguous.
 
Another thing to keep in mind when setting up your main grounding system in virtually any situation is that regardless of, and independent of the fact that the NEC requires the integration and bonding of all available grounding electrodes listed in article 250; that from a logical/safety standpoint, it's really more or less just a universally good idea in general. If you stop and think about it; What is the one electrical parameter/characteristic of a grounding electrode system, that you, the designer/installer of the system; have a certain latitude of control over, which will ultimately determine how effective your grounding system will be if/when the time comes for it to do it's job and save lives. The answer to this of course, is the total impedance of the ultimate path(s) your fault current takes between you; who just dropped a large hex wrench between the main service lug and the panel frame, and the giant floating rock we live on. The lower the total impedance between your system and the earth, the greater the fault current you are capable of safely carrying and channeling away from John C. Bystander; therefore the better a grounding system it will ultimately be. With this all in mind; you essentially have two ways of doing this; 1) By increasing the size of your grounding electrodes, and 2) By creating more parallel paths to the Earth. Since the AWG of your copper conductors are fixed once they are installed and in place; by utilizing as many parallel earthed grounding paths as you possibly can and have available for you to use in your system, the lower your impedance to earth will be, and the better the chance your grounding system can be depended on to save your life when the "oh my, that was a terrible idea" moment with worst-case scenario fault currents, ends up happening.

So the moral of the story is that for any standard low-impedance grounding system; the lower you can get that total impedance, the safer you've made your electrical system. By always using as many parallel grounding paths to earth as you have available to your system, you'll therefore always be optimizing your system to be the best that you could have built it to be.
 
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The Great Sarducci said:
Another thing to keep in mind when setting up your main grounding system in virtually any situation is that regardless of, and independent of the fact that the NEC requires the integration and bonding of all available grounding electrodes listed in article 250; that from a logical/safety standpoint, it's really more or less just a universally good idea in general. If you stop and think about it; What is the one electrical parameter/characteristic of a grounding electrode system, that you, the designer/installer of the system; have a certain latitude of control over, which will ultimately determine how effective your grounding system will be if/when the time comes for it to do it's job and save lives. The answer to this of course, is the total impedance of the ultimate path(s) your fault current takes between you; who just dropped a large hex wrench between the main service lug and the panel frame, and the giant floating rock we live on. The lower the total impedance between your system and the earth, the greater the fault current you are capable of safely carrying and channeling away from John C. Bystander; therefore the better a grounding system it will ultimately be. With this all in mind; you essentially have two ways of doing this; 1) By increasing the size of your grounding electrodes, and 2) By creating more parallel paths to the Earth. Since the AWG of your copper conductors are fixed once they are installed and in place; by utilizing as many parallel earthed grounding paths as you possibly can and have available for you to use in your system, the lower your impedance to earth will be, and the better the chance your grounding system can be depended on to save your life when the "oh shit, that was a terrible idea" moment with worst-case scenario fault currents, ends up happening.

So the moral of the story is that for any standard low-impedance grounding system; the lower you can get that total impedance, the safer you've made your electrical system. By always using as many parallel grounding paths to earth as you have available to your system, you'll therefore always be optimizing your system to be the best that you could have built it to be.
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This is a complete misunderstanding of the Grounding Electrode System and its function in an electrical system.

Grounding electrodes and conductors have nothing to do with fault clearing and reliance on them to do so would make a more dangerous system.
 
While the pipe coming into the house may be metal, if it's like here the water co. ran new plastic 15 years ago and tied in above ground to that metal with plastic, meaning it isnt a proper grounding electrode anymore.
 
ActionDave said:
This is a complete misunderstanding of the Grounding Electrode System and its function in an electrical system.

Grounding electrodes and conductors have nothing to do with fault clearing and reliance on them to do so would make a more dangerous system.
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Agreed!

Chris
 
ActionDave said:
This is a complete misunderstanding of the Grounding Electrode System and its function in an electrical system.

Grounding electrodes and conductors have nothing to do with fault clearing and reliance on them to do so would make a more dangerous system.
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+1

The Great Sarducci said:
the total impedance of the ultimate path(s) your fault current takes between you; who just dropped a large hex wrench between the main service lug and the panel frame, and the giant floating rock we live on.
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In that scenario the grounded service conductor carries nearly all the fault current, chances are the grounding electrode is high enough resistance it carries very little current in comparison. There will still be voltage gradients in the vicinity as well. Unless you are barefoot on a grounded surface you likely aren't subject to enough gradient to feel anything though, especially on a 120 to ground system, 2400 volt system - different story.
 
ActionDave said:
This is a complete misunderstanding of the Grounding Electrode System and its function in an electrical system.

Grounding electrodes and conductors have nothing to do with fault clearing and reliance on them to do so would make a more dangerous system.
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I agree too, the conversation should be about the main bonding jumper not the grounding electrodes.
 
ActionDave said:
This is a complete misunderstanding of the Grounding Electrode System and its function in an electrical system.

Grounding electrodes and conductors have nothing to do with fault clearing and reliance on them to do so would make a more dangerous system.
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Add another in agreement.

Roger
 
The Great Sarducci said:
The answer to this of course, is the total impedance of the ultimate path(s) your fault current takes between you who just dropped a large hex wrench between the main service lug and the panel frame, and the giant floating rock
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I'd agree with this if the "Giant Floating Rock" was a vivid description of the Neutral point on a "Pole Top" Transformer. :)

JAP>
 
Unfortunately, I think my answer may have been misconstrued. To start, I never said anything about using the EGC to clear an electrical fault. Obviously it’s the OCPD which clears a fault. And yes, I understand that in the case of an arc fault, a low impedance path to ground will of course make the situation worse because it will in turn draw a much larger fault current; making the arc a much hotter/more destructive force. I get that, and also get how my using of an example which would result in arc flash was probably a poor choice for highlighting the safety benefit of a well-grounded system. Looking back at my post, I would choose a different example. But one thing that I think we can probably all agree on, and what I was trying to illustrate in my post is that THE purpose of proper grounding/bonding is to provide a conductive path to intentionally, and safely channel current through a normally non-current carrying medium, to earth. “Effective Ground Fault Current Path” as defined in Art. 100 of the NEC would have perhaps been a better term to use to illustrate my intent. Of course grounding isn’t always a good thing, and I agree, it can make matters worse, such as in the case of arc flash. Will grounding/bonding prevent or minimize the unique hazards that exist in that situation? Of course not; BUT, when a fault does occur, it will also likely prevent someone from being electrocuted when they come into direct contact with the bonded metallic surfaces that have unintentionally become a part of the electrical circuit. Is a lower impedance to ground a problem in this case? Absolutely not. In fact, we want it to be as low as possible so that a higher fault current can be drawn thru the breaker/fuse, and maintained just long enough to allow this device to effective open the circuit. Of course, the faster this can be achieved, the better as even fractions of a second matter a whole hell of a lot when SCC is in the 10's of kA. If we do not design our grounding system properly, and the overall impedance to earth is too high (usually considered as >25W ); not only will it take longer for the OCPD to effectively clear the fault; resulting in far more damage, but it may also allow for a substantial voltage potential to exist at the exposed energized surface where it should be designed to be kept as close to 0V as possible so that somebody doesn’t die when they are in a situation where their body can provide a nice competitive path to ground for this remaining potential, where it should have never been in the first place if the system was better earthed in the first place.
Again I realize and agree that from the way in which I worded my original response; it’s understandable to me how one could misconstrue it to mean something entirely different than what I had intended. For that I am actually glad that you guys called it out. This gave me the opportunity to give my post a 2nd look so that I could provide more clarity on something that I should have written out better the first time around.
Anyway, hopefully I’ve cleared some things up regarding what may have been fairly, but also falsely perceived as a poor or total lack of understanding of EGCs and their purpose.
 
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The Great Sarducci said:
Unfortunately, I think my answer may have been misconstrued. To start, I never said anything about using the EGC to clear an electrical fault. Obviously it’s the OCPD which clears a fault.
It clears through the EGC (other than L-L faults). That is its sole purpose in life.

And yes, I understand that in the case of an arc fault, a low impedance path to ground will of course make the situation worse because it will in turn draw a much larger fault current; making the arc a much hotter/more destructive force.
That is also not true. A higher current draw might well cause the upstream OCPD to trip much faster thus causing far less incident energy to be discharged.

I get that, and also get how my using of an example which would result in arc flash was probably a poor choice for highlighting the safety benefit of a well-grounded system. Looking back at my post, I would choose a different example. But one thing that I think we can probably all agree on, and what I was trying to illustrate in my post is that THE purpose of proper grounding/bonding is to provide a conductive path to intentionally, and safely channel current through a normally non-current carrying medium, to earth.
The earth is NEVER supposed to be an intentional part of the fault clearing path.

“Effective Ground Fault Current Path” as defined in Art. 100 of the NEC would have perhaps been a better term to use to illustrate my intent. Of course grounding isn’t always a good thing, and I agree, it can make matters worse, such as in the case of arc flash. Will grounding/bonding prevent or minimize the unique hazards that exist in that situation? Of course not; BUT, when a fault does occur, it will also likely prevent someone from being electrocuted when they come into direct contact with the bonded metallic surfaces that have unintentionally become a part of the electrical circuit. Is a lower impedance to ground a problem in this case? Absolutely not. In fact, we want it to be as low as possible so that a higher fault current can be drawn thru the breaker/fuse, and maintained just long enough to allow this device to effective open the circuit. Of course, the faster this can be achieved, the better as even fractions of a second matter a whole hell of a lot when SCC is in the 10's of kA. If we do not design our grounding system properly, and the overall impedance to earth is too high (usually considered as >25W );
Once again, the earth is NEVER supposed to be an intentional part of the fault clearing path. the impedance between the GEC and earth really just does not matter much.

not only will it take longer for the OCPD to effectively clear the fault; resulting in far more damage, but it may also allow for a substantial voltage potential to exist at the exposed energized surface where it should be designed to be kept as close to 0V as possible so that somebody doesn’t die when they are in a situation where their body can provide a nice competitive path to ground for this remaining potential, where it should have never been in the first place if the system was better earthed in the first place.
Again I realize and agree that from the way in which I worded my original response; it’s understandable to me how one could misconstrue it to mean something entirely different than what I had intended. For that I am actually glad that you guys called it out. This gave me the opportunity to give my post a 2nd look so that I could provide more clarity on something that I should have written out better the first time around.
Anyway, hopefully I’ve cleared some things up regarding what may have been fairly, but also falsely perceived as a poor or total lack of understanding of EGCs and their purpose.
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I think you have some serious misunderstandings about some of these topics.
 
petersonra said:
I think you have some serious misunderstandings about some of these topics.
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That may be an understatement.

Mr. Sarducci, please hit your spacebar every now and then, your posts are very difficult to read.

Roger
 
Sarducci, I would recommend for starters reading the Sticky in the grounding and bonding page. It covers these basic grounding myths.

connecting equipment to earth/dirt is of relatively little importance. Other than perhaps a few specialized applications, for low voltage wiring, the resistance achieved by a grounding electrode system really doesnt matter.
 
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