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Thread: Purpose of Grounding Electrode System

  1. #21
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    Quote Originally Posted by MAC702 View Post
    This has a 2004 copyright at the bottom. Does this address what you are thinking?

    https://www.mikeholt.com/mojonewsarc...h~20040602.php
    Very nice MAC. That TN system that Norway uses is exactly what we used in hospital OR's. The equipment grounds and neutrals were left separate- not bonded. The pros to that system is that you can not get shocked through grounded metal parts. The cons is that it won't clear a fault either, as faulted current can't jump back to the neutral and trip a breaker. They use some sort of extra monitoring devices that I didn't get a chance to further explore- a third party calibrated the special equipment.

    Even then, that doesn't have to do with a GES. That has to do with bonding the non-current carrying metal likely to become energized with the neutral to clear a fault.

    That engineer emailing Mike Holt states in his conclusion:


    • The grounding of the distribution system is NOT NECESSARY for the system itself; it's only useful when providing protection against lightning. The line voltage protections should be referred to the neutral or common point, a line that should be provided even if not needed for the distribution itself.


    While ground rods protect against lightning they can also carry current in a fault to earth though this is not their intended use- the earth has too much resistance to clear a fault. It's also why we only have to size our ground rod GEC's to #6. You can have a 40 story building with a 4000 amp 480v service and you still will only need #6 to ground rods. Bonding to water pipe as GE we follow 250.66 because we have to consider the service potentially energizing the water pipes.

    Maybe I'm off base in a matter of semantics.

    The purpose of grounding (to earth) our electrical systems is for lightning, static, and other foreign voltages. A water pipe is exceptional as it can run along with the electrical system throughout the building and is to be apart of the GEC system. But a ground rods purpose is NOT to clear faults or protect against shock from our systems.

  2. #22
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    Quote Originally Posted by ActionDave View Post
    It's a common point and is easy to find and connect to.

    If there were a better way it would have been implemented. We've been solidly grounded for almost a century now. More than that if you go back to the telegraph days.
    I'm not saying there's a better way- although we've found out there is in the Norway/OR example which is expensive. I'm saying I've gotten into too many debates with electricians who think ground rods are for clearing faults or that when they get shocked it's electricity passing through them to the earth.

    Electricity always returns to it's source. We bond the metal parts to neutral to clear a fault and that's usually the same reason we get shocked.

    We drive ground rods for lightning.

  3. #23
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    Quote Originally Posted by daytonajim00 View Post
    So electrofelon, you are saying that grounding (to earth) our systems is about the potential between conductors and earth, OCPD's, and clearing faults?
    Yes, but note by "clearing faults" I dont mean that dirt will clear a fault. What I mean is whether the system is grounded or not determines what happens during a first fault. An ungrounded system becomes a grounded system after a first fault. This isnt really a safety issue, unless its an intermittent arcing fault which can result in a phenomenon where voltage can rise excessively and cause damage, or maybe the capacitive charging current could result in enough sparking to start a fire. A first fault on a grounded system causes high fault currents and trip the breaker. So one advantage of ungrounded systems is low fault currents on a first fault. An advantage of grounded systems is the first fault is handled automatically alerting the user that there is an issue because of the tripped breaker.


    Another advantage of grounded systems is they are a bit more economical. Look at a single phase utility MGN system and you will see why: Only one conductor needs a high insulation level, only one conductor needs a fuse/cutout, and the transformer primary only needs one bushing. If were a "delta" (two phases from a delta system) then both conductors would need a a high BIL, fuse, and bushing.

    So as you can see, system grounded determines the general construction of the electrical system and how it functions during faults.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  4. #24
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    Quote Originally Posted by daytonajim00 View Post
    Very nice MAC. That TN system that Norway uses is exactly what we used in hospital OR's. The equipment grounds and neutrals were left separate- not bonded. The pros to that system is that you can not get shocked through grounded metal parts. The cons is that it won't clear a fault either, as faulted current can't jump back to the neutral and trip a breaker. They use some sort of extra monitoring devices that I didn't get a chance to further explore- a third party calibrated the special equipment.
    IT technically- and I disagree. In hospital ORs all EGC are bonded together- Norway made the mistake of not bonding between structures resulting in fires. Meaning structure 1 would have an A phase ground fault and structure 2 might have a B phase fault creating 230 volts potential between structures. A beautiful idea ruined again by what again I think is a global misunderstanding of what is grounding and what is bonding.

    As such RCDs are now recommend as the system is basically a TT at most times. TT systems need grounding electrodes to clear a fault btw.
    I'm in over my head...

  5. #25
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    Quote Originally Posted by jaggedben View Post
    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.
    but that is equipment bonding and earthing and has nothing to do with SYSTEM grounding.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  6. #26
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    Quote Originally Posted by electrofelon View Post
    A first fault on a grounded system causes high fault currents and trip the breaker. So one advantage of ungrounded systems is low fault currents on a first fault. An advantage of grounded systems is the first fault is handled automatically alerting the user that there is an issue because of the tripped breaker...

    So as you can see, system grounded determines the general construction of the electrical system and how it functions during faults.
    This is my problem with the word "grounded". If you subtract the GES but still have the main bonding jumper of all metal parts to neutral is the system grounded?

    Definitions say grounded as Connected to ground
    Definitions say ground is to earth

    If a system is not grounded as you say I read it as it is not connected to earth. That does not affect faults IMO. Now BONDING like the MBJ being subtracted in the TN systems I talked about would and they make expensive counter measures for that.

    Let me also exemplify Article 250.4 General Requirements for Grounding and Bonding
    (a) (1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.

    This is my issue with the words grounding and bonding. I feel like too many mistake grounding for having much to do with the MBJ and clearing a fault.

  7. #27
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    Quote Originally Posted by mbrooke View Post
    IT technically- and I disagree. In hospital ORs all EGC are bonded together- Norway made the mistake of not bonding between structures resulting in fires. Meaning structure 1 would have an A phase ground fault and structure 2 might have a B phase fault creating 230 volts potential between structures. A beautiful idea ruined again by what again I think is a global misunderstanding of what is grounding and what is bonding.

    As such RCDs are now recommend as the system is basically a TT at most times. TT systems need grounding electrodes to clear a fault btw.
    I don't know about Norway and just discovered that it was called IT but I can tell you it's definitely used in modern OR's. Of course all EGC are bonded together. It's the neutrals on that very SDS which are not bonded to the EG's.

  8. #28
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    Quote Originally Posted by mbrooke View Post
    Norway made the mistake of not bonding between structures resulting in fires. Meaning structure 1 would have an A phase ground fault and structure 2 might have a B phase fault creating 230 volts potential between structures.
    But that would only be an issue if serving the structures from a common transformer. Of course serving each structure with its own transformer gets expensive.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  9. #29
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    Quote Originally Posted by daytonajim00 View Post
    I don't know about Norway and just discovered that it was called IT but I can tell you it's definitely used in modern OR's. Of course all EGC are bonded together. It's the neutrals on that very SDS which are not bonded to the EG's.
    Yup- it is indeed used in modern ORs.

    Quote Originally Posted by electrofelon View Post
    But that would only be an issue if serving the structures from a common transformer. Of course serving each structure with its own transformer gets expensive.


    100% true, however, sadly, A single transformer often feeds 100 homes. Had they bonded everything together, the concept would have been a much safer one. But in any case it shows you the importance of bonding in any power system.
    I'm in over my head...

  10. #30
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    Quote Originally Posted by ActionDave View Post
    ...If there were a better way it would have been implemented. We've been solidly grounded for almost a century now. More than that if you go back to the telegraph days.
    Not to disagree, exactly, but my understanding is that France and Japan adopted new and quite different (TT) systems after WWII, when everything in those places was destroyed enough that it didn't cost too much to essentially start from scratch. So sometimes things keep getting done a certain way because it's too expensive to change the entire system at once, rather than because there isn't a better way.

    Quote Originally Posted by daytonajim00 View Post
    ...
    While ground rods protect against lightning they can also carry current in a fault to earth though this is not their intended use- the earth has too much resistance to clear a fault. It's also why we only have to size our ground rod GEC's to #6. You can have a 40 story building with a 4000 amp 480v service and you still will only need #6 to ground rods. Bonding to water pipe as GE we follow 250.66 because we have to consider the service potentially energizing the water pipes.

    Maybe I'm off base in a matter of semantics.

    The purpose of grounding (to earth) our electrical systems is for lightning, static, and other foreign voltages. A water pipe is exceptional as it can run along with the electrical system throughout the building and is to be apart of the GEC system. But a ground rods purpose is NOT to clear faults or protect against shock from our systems.
    I think you should be careful thinking that the NEC required GES does much, if anything, to help with lightning. I think it's definitely the case that some people who've had a hand in writing the code think that. But my understanding is that in reality it's not going to help all that much. Poor grounding practices can also make lightning problems worse. I think even some NEC required grounding practices could make issues with lightning worse, given some bad luck. If you want real lightning protection, there are SPDs which the NEC does not require, and there's NFPA 780 for lightning protection systems.

    Again, the GES potentially does a lot of different things, I think some of which you are grasping and some of which you aren't yet.

    Quote Originally Posted by daytonajim00 View Post
    We drive ground rods for lightning.
    And some other stuff, which you mentioned. And some other stuff that you don't seem to be accepting. By the way, have you read what the NEC actually says the purpose of grounding is? It's 250.4(A)(1) and (2). (2) in particular is very, very general and I believe is motivated by what I said in post 3.

    Quote Originally Posted by daytonajim00 View Post
    This is my problem with the word "grounded". If you subtract the GES but still have the main bonding jumper of all metal parts to neutral is the system grounded?
    If it's a service, it's probably still grounded somewhere else. If it's an SDS, no, the system is no longer grounded. By the way, the NEC allows some systems to be ungrounded by design. But those systems should still have a GES, and the NEC requires it.

    This is my issue with the words grounding and bonding. I feel like too many mistake grounding for having much to do with the MBJ and clearing a fault.
    It's certainly correct that too many are confused, and the traditional use of 'Equipment Grounding Conductor' in the US is partly to blame. EGCs are for bonding, not grounding per se. And clearing faults using OCPDs is the primary reason for bonding. But, there are still other reasons to ground the same stuff. EGCs ultimately ground stuff as well, if they are ultimately connected to a GES.

    There are also different kinds of faults and different kinds of fault protection, and different ways designing systems to deal with them. In systems that rely on RCDs and similar devices to clear faults, the GES is still important to clearing faults as well.

    Quote Originally Posted by electrofelon View Post
    but that is equipment bonding and earthing and has nothing to do with SYSTEM grounding.
    I'm not quite sure what your point is. Did the OP originally ask about system grounding? In the US, earthing and system grounding tend to be quite conflated. In other countries it might be less so.

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