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Thread: Purpose of Grounding Electrode System

  1. #1
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    Purpose of Grounding Electrode System

    Hello everyone,

    I've been a following the forums for years now and have finally joined.

    For whatever reason, grounding and bonding seems like the most misunderstood sections in the electrical field- at least on the construction end. Either I understand some things wrong or most other electricians I've met do. The specific topics I most frequently get into debates about are as follows:

    An electrical system must have a grounding electrode system. Grounding electrodes are buried metal, like ground rods, water pipe, etc., per NEC, that connect to our electrical system, offering zero potential to ground.

    Why do we make a purposeful connection to earth is where the debate comes in. Many responses are "to clear faults" or "to assist in opening a breaker during a fault" or "to protect against electrical shock".

    I thought our connection to earth has nothing to do with clearing a fault. So let's consider a fault: electricity needs a path back to its source to flow. During a fault current flows onto the intentionally bonded surface, back to the main bounding jumper, on to the neutral, offering a complete circuit (home) of low resistance at which point a properly functioning breaker will trip.

    So what is the point of the ground rod (GE) then?

    I always thought a ground rod- or any other GE's main purpose is to offer zero potential between the bonded metal parts of our electrical system and earth. This is done to quickly 'drain' foreign voltages like lightning, static, and other abnormal surges."

    I've read other reasons why the GE system is required... As far as tethering our service down to stabilize voltages during normal operation I'm not sure about. I've installed systems that were not bonded by design. These were operating room SDS's in hospitals where the neutral was always completely floating. Voltages seemed fine.

    I think a lot of confusion comes from the word 'ground' and people automatically think earth. I think they see the ground rods as the 'master component' of the equipment grounds we usually include throughout the system. Add to the mix the 'grounded conductor' (neutral) and most apprentices get totally lost. I was for the first four years. I was never taught correctly.

    So what I'm saying is please correct me if I'm wrong. 95% of the electricians I've met think the GE system has something to do with the voltages we use (utility or emergency standby).

    What does the community think?
    Last edited by daytonajim00; 09-22-18 at 12:36 PM.

  2. #2
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    I like to say that system grounding isn't about safety, it's just a system topology. It effects the potential between the various conductors and earth, the number and placement of OCPD's, and how faults are handled.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #3
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    The purpose is multifold, but is generally to remove any potential between the earth and exposed bonded metal parts, so that no one standing on the earth in bare feet who touches a bare metal part will get electrocuted. There a variety of ways that a potential difference could end up in unintended places. In the US it is also significant that we use a grounded conductor as a fault clearing path. However, my understanding is that even in countries where they don't do that, they still ground expose metal non-current carrying parts, just in case an ungrounded system becomes unintentionally grounded.

  4. #4
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    So electrofelon, you are saying that grounding (to earth) our systems is about the potential between conductors and earth, OCPD's, and clearing faults?

    Jaggedben, you are saying that grounding (to earth) our systems is about the making equal the potential between exposed bonded metal parts, to protect people in bare feet from electric shock?

    Let me give a scenario and use both of those responses. Scenario is there is NO grounding electrode system installed but all metal parts are bonded and all circuits have equiptment grounds going back to the main in which the neutral is bonded. Basically a normal system minus the GE's.

    Electrofelon, should a fault occur in this system, would it not find its way back to the neutral and trip the breaker?

    Jaggedben, since electricity needs to flow back to neutral for one to get shocked, would the removal of the grounding electrodes make a difference? If anything, becoming energized in bare feet with ground rods installed would increase the chance of current flowing and one getting shocked. The current would have that much better of a path: through the slab, across the ground, up the ground rod's GEC, onto the neutral.

    Like I said, perhaps I have had it wrong, but this is exactly like other conversations I've had.

  5. #5
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    Quote Originally Posted by daytonajim00 View Post
    ...

    Jaggedben, since electricity needs to flow back to neutral for one to get shocked, would the removal of the grounding electrodes make a difference?
    Well, let's say the utility neutral fails open, then it would make a pretty big difference. Now the current will try to flow from any bonded metal, through a person with bare feet, to the earth, and back to the grounded neutral node at the utility transformer.

    If anything, becoming energized in bare feet with ground rods installed would increase the chance of current flowing and one getting shocked.
    No, it wouldn't.

    The current would have that much better of a path: through the slab, across the ground, up the ground rod's GEC, onto the neutral.
    ...
    That would only happen if the metal you touched wasn't already properly bonded to the service neutral with an EGC, which is its own hazard. Even if there were no ground rod and GEC locally, you could still get shocked by that metal, because the neutral is grounded back at the utility transformer as well. Having a local grounding electrode system doesn't meaningfully increase that hazard.

  6. #6
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    Quote Originally Posted by jaggedben View Post
    Well, let's say the utility neutral fails open, then it would make a pretty big difference. Now the current will try to flow from any bonded metal, through a person with bare feet, to the earth, and back to the grounded neutral node at the utility transformer.
    ...
    I should add, it would even worse if, in the course of responding to an open utility neutral, someone happens to touch both an electrical conduit and a cold water pipe that goes underground to the street. That water pipe is a functional electrode, so now the person becomes a GEC. If there is already a code compliant low-impedance GEC, then significant current will already be flowing, and the voltage drop between those two pieces of metal will be negligible. The negligible voltage drop is what the person will experience instead of possibly a voltage higher than the line-neutral voltage.

  7. #7
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    Welcome to MH Jim

    First, i would encourage you to go here ,as MH's forum is international

    2ndly, know that we exist on one big nuetral , the closer to substations one gets , the more this applies.

    3rd, Tesla was right

    more as the crew opines

    ~RJ~

  8. #8
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    Quote Originally Posted by jaggedben View Post
    Well, let's say the utility neutral fails open, then it would make a pretty big difference. Now the current will try to flow from any bonded metal, through a person with bare feet, to the earth, and back to the grounded neutral node at the utility transformer.
    If the neutral on the utility failed open, I would guess an electrician is on the way because no single phase circuit using a neutral would be working. In the event that a fault on a piece of metal happened directly after said neutral failure, I can see a hazard laying await. Whether you had a GES apart of that building or not would not matter, the hazard would be the same: there would not be enough conductivity through the earth to clear the fault. This is why, to my understanding, the GES has nothing to do with clearing faults. I could be misunderstanding something but what you explained is a doomsday scenario. It's also the reason why every electrician should know the theory behind all of this. When going on a call never assume anything. I would use an amp probe on the GEC even if everything seems to be working fine. Voltage is easy to see. Current is the invisible killer.

    Quote Originally Posted by jaggedben View Post
    That would only happen if the metal you touched wasn't already properly bonded to the service neutral with an EGC
    I was thinking more in line with becoming energized from an ungrounded conductor. But I can see what you mean that it doesn't make a difference because the utility transformer in grounded as well. The only difference is there would be more earth to have to travel through for the current to make it there.
    Last edited by daytonajim00; 09-22-18 at 04:52 PM.

  9. #9
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    We should invite Mr Kirchoff into this thread... ~RJ~

  10. #10
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    Quote Originally Posted by romex jockey View Post
    We should invite Mr Kirchoff into this thread... ~RJ~
    Or Mike Holt. They wrote an article titled"Ground Rod Does Not Assist in Clearing a Fault"


    https://www.mikeholt.com/technical-g...(01-25-2K).php

    And before the thread gets off topic- which is cool too- I would just like to bring it back to my original point. Why do we bond our electrical systems to earth?

    Is it for lightning, static, and other foreign surges like I thought or is there something I'm missing?

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