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    #16
    I think I might have confused you. No, I didn't say bonding D enclosure directly to neutral conductor in D, but rather bonding D to A, where A is the service disconnect with grounded neutral.

    Comment


      #17
      Originally posted by Brian Dang View Post
      I think I might have confused you. No, I didn't say bonding D enclosure directly to neutral conductor in D, but rather bonding D to A, where A is the service disconnect with grounded neutral.
      If I was confused, that's probably because your writing was not clear at all. Assuming metallic boxes, bonding D to A is accomplished by normal installation practice, although it will touch B and C along the way. That is, unless you mean adding a separate conductor directly from D to A but that won't add much of anything.

      What you did not say is "run an insulated conductor from the receptacle or utilization equipment all the way back to the SSBJ", but even that wouldn't do much good unless the equipment itself is completely isolated from all other "grounds", which can be hard to do for anything bigger than a toaster. (Search around these forums for more about "isolated grounds".)

      And running to the actual service disconnect would not be a good idea if the equipment is supplied by an SDS. Heck, it might not be possible at all.

      Comment


        #18
        Originally posted by zbang View Post
        If I was confused, that's probably because your writing was not clear at all. Assuming metallic boxes, bonding D to A is accomplished by normal installation practice, although it will touch B and C along the way. That is, unless you mean adding a separate conductor directly from D to A but that won't add much of anything.

        What you did not say is "run an insulated conductor from the receptacle or utilization equipment all the way back to the SSBJ", but even that wouldn't do much good unless the equipment itself is completely isolated from all other "grounds", which can be hard to do for anything bigger than a toaster. (Search around these forums for more about "isolated grounds".)

        And running to the actual service disconnect would not be a good idea if the equipment is supplied by an SDS. Heck, it might not be possible at all.
        You are still confused. Since I know what an isolated ground is, I fully understand what Brian was saying, both times. When he said run back he meant electrically. If I have a single 20A IG circuit I can legally take the green wire (with yellow stripe allowed) and run it to and through the branch panel, through the conduit containing its feeder and continue until I get to the physical location where the neutral and the ground are bonded together as required in NEC 250. That is what Brian clearly meant. Or I can run an isolated ground wire from that service bond to each subpanel terminating on a separate isolated ground bus that is physically just like a neutral bus, which I can then land the incoming wires from the receptacle feeding the piece of equipment. In any case an isolated ground extends from the receptacle to the bonding point of the service or separately derived system without touching ground along the way, period.

        You supposition about isolating the equipment itself is not relevant. What happens when the equipment is plugged in to the outlet is for them to design. If they are concerned about exposed metal parts being unintentionally grounded they can design it so they don't have any.


        I know what I don't know, and I know where to go to find it!

        Comment


          #19
          Originally posted by zbang View Post
          ...but even that wouldn't do much good unless the equipment itself is completely isolated from all other "grounds", which can be hard to do for anything bigger than a toaster. (Search around these forums for more about "isolated grounds".)
          I have hundreds of pieces of equipment, most mounted in standard 19" racks (some larger), which all utilized a single-point ground. Mine is just one of hundreds of facilities that use this method.

          It can, and is, done.

          You must only have one ground. How your equipment gets there is up to you.
          Kirchoff and Ohm...the only laws that make sense

          Comment


            #20
            Originally posted by cuba_pete View Post
            I have hundreds of pieces of equipment, most mounted in standard 19" racks (some larger), which all utilized a single-point ground. Mine is just one of hundreds of facilities that use this method.

            It can, and is, done.

            You must only have one ground. How your equipment gets there is up to you.
            Help me out here.

            How does the IG stay isolated when it is connected to multiple pieces of equipment on a metal rack?

            Comment


              #21
              Originally posted by iwire View Post
              How does the IG stay isolated when it is connected to multiple pieces of equipment on a metal rack?
              Every data center I've been in has a bonding wire to the rack, the rack/cabinet is bolted to the raised floor (and it's frame is bonded), the PDU has an EGC from it's source, and the actual computers connect the EGC to their chassis. Which is bolted into the cabinet. If you run all of those bonding connections back to a single connection, and if everything is insulated from the GES, then you have a single point ground, but I wouldn't call that an isolated ground.

              And no, I don't think I'm confused about what an isolated ground is (see also 250.96(B), 250.146(D), and 406.3), but I'm not going to get into the semantics and writing style.

              Comment


                #22
                Originally posted by zbang View Post
                Every data center I've been in has a bonding wire to the rack, the rack/cabinet is bolted to the raised floor (and it's frame is bonded), the PDU has an EGC from it's source, and the actual computers connect the EGC to their chassis. Which is bolted into the cabinet. If you run all of those bonding connections back to a single connection, and if everything is insulated from the GES, then you have a single point ground, but I wouldn't call that an isolated ground.
                Which is what I see as well.

                But I also see folks insist on IGs and IG outlets at each rack outlet which to me is foolish as they all become common at the rack as soon as you plug equipment in there.

                Comment


                  #23
                  Originally posted by iwire View Post
                  Help me out here.

                  How does the IG stay isolated when it is connected to multiple pieces of equipment on a metal rack?
                  This is another case where the language and nomenclature used by the NEC, electricians, engineers, laymen, etc. gets confusing.

                  Of the 14 times that the term "isolated ground(ing)" appears in the 2014 NEC, almost exclusively followed by "receptacle".

                  Excerpted from the NEC:
                  250.96(B) Isolated Grounding Circuits
                  406.3(D) Isolated Grounding Conductor
                  406.3(D)(2) Exception: Isolated Ground Receptacle
                  517.16 Isolated Ground Receptacle
                  250.146(D) Isolated Ground Receptacles
                  406.3(D) Isolated Ground Receptacles
                  406.3(D)(2) Isolated Ground Receptacles
                  517.16 Isolated Ground Receptacles
                  640.7(C) Isolated Ground Receptacles
                  647.7(B) Isolated Ground Receptacles
                  647.7(B) Isolated Ground Receptacles
                  640.7(C) Isolated Grounding-type Receptacles
                  645.15 Informational Note No. 2: Isolated Grounding-type Receptacles
                  250.184(B) Single-Point Grounded Neutral System

                  Whereas the only time that the term "Isolated Ground" is found alone in the 2014 NEC is in the Index, and actually refers to section 517.16 which is, you guessed it, a section on "Use of Isolated Ground Receptacles":

                  Index Isolated Ground 517.16 (section actually titled) "Use of Isolated Ground Receptacles"

                  However...

                  The term single point ground:

                  250.184 single point grounded
                  250.184(B) Single-Point Grounded Neutral System
                  250.184(B) Single-Point Grounded Neutral System
                  250.184(B)(1) Single-Point Grounded Neutral System
                  250.184(B)(1)b. Single-Point Grounded Neutral System

                  And "single point" where relevant to the discussion:
                  250.30(A)(1) single point

                  A complete Single Point grounding scheme is not fully (or even at all...) explained in the NEC.

                  Learning is for school. The NEC just gives us the minimum standards allowable for a "safe" installation (according to the insurance-industry-driven NFPA). There is a lot more to electrical theory, practice and the resultant installation than what is found in the NEC.

                  ...but I digress...

                  An isolated ground receptacle (250.146 (D)) means that the ground is not continuous to the mounting of the receptacle. It is literally isolated from the box and is not, when made fast, bonded nor continuous to the box, raceway, and all other items which are bonded...at that point. At the point where the grounds come together, the single point, is where the system is then made electrically safe and meets the intended need of the system in reducing noise or for other purposes as necessary.

                  A single point ground merely utilizes isolated ground receptacles to achieve the overall system isolation. This allows the boxes, raceways, etc. (exposed and available conductive parts) to be bonded for safety while allowing for the isolation and protection from EMF and other effects on the grounding conductor.

                  ...again, I digress...

                  In your example, when connected to multiple pieces of equipment on (in) a metal rack:

                  The power distribution unit (receptacle), surge suppressor, power strip, etc. is provided an isolated ground receptacle with a dedicated ground which is isolated from any and all bonded raceways, enclosures, building steel, counterpoises, etc. until it reaches either the main service or separately derived service, as applicable. Equipment racks (cabinets, housings, mountings, etc.) used isolated mounting hardware to keep it clear of stray connections to any bonded equipment. A grounding bar, also isolated from the cabinet except at one point (EGC/bonding conductor) is made fast and all EGC's for all rack mounted equipment are attached there. Equipment in the cabinet may also be provided with isolation mounts if necessary (i.e., excessive noise from a power supply at a nuisance frequency), but the EGC must be maintained. All grounding bars and plates for a particular system/installation/cabinet/rack/etc., as applicable must be bonded to the same service where power is derived...this is important for obvious (and NEC derived) reasons.

                  There is a lot more that goes into this, but the whole point is to properly understand and then make use of Kirchoff's observations and to keep circulating currents (EMF induced or vice-versa) whether power system or equipment derived from getting into areas which they is not desired (causing problems). There are endless types of "interference" and the resultant safe and legal methods which can be used to mitigate issues are simply the best way (cheap, easy, quick...pick two) of getting the job done.

                  The IEEE Green (Std 142), Emerald (Std 1100), Standard 3000, and Standard 3003 lay this all out nicely. The NEC and several other documents regularly reference (quoting and interpreting) these engineering standards which can also be directly referenced for exceptional installations of equipment with a very electro-sensitive nature.

                  This is not hypothesis, theory, conjecture, or some sort of hit-and-miss practice. These use of these (now considered) exceptions have a proper time and place for implementation. I agree that they can and have been abused, used as band-aids, and poorly implemented by many people, but that doesn't mean that each instance is nothing but hogwash.

                  I have personally been utilizing single-point grounding methods for nearly 30 years, building on knowledge and practice of over 100 years in my field alone.

                  Works fine...lasts a long time.
                  Kirchoff and Ohm...the only laws that make sense

                  Comment


                    #24
                    Originally posted by cuba_pete View Post
                    This is another case where the language and nomenclature used by the NEC, electricians, engineers, laymen, etc. gets confusing.

                    Of the 14 times that the term "isolated ground(ing)" appears in the 2014 NEC, almost exclusively followed by "receptacle".

                    Excerpted from the NEC:
                    250.96(B) Isolated Grounding Circuits
                    406.3(D) Isolated Grounding Conductor
                    406.3(D)(2) Exception: Isolated Ground Receptacle
                    517.16 Isolated Ground Receptacle
                    250.146(D) Isolated Ground Receptacles
                    406.3(D) Isolated Ground Receptacles
                    406.3(D)(2) Isolated Ground Receptacles
                    517.16 Isolated Ground Receptacles
                    640.7(C) Isolated Ground Receptacles
                    647.7(B) Isolated Ground Receptacles
                    647.7(B) Isolated Ground Receptacles
                    640.7(C) Isolated Grounding-type Receptacles
                    645.15 Informational Note No. 2: Isolated Grounding-type Receptacles
                    250.184(B) Single-Point Grounded Neutral System

                    Whereas the only time that the term "Isolated Ground" is found alone in the 2014 NEC is in the Index, and actually refers to section 517.16 which is, you guessed it, a section on "Use of Isolated Ground Receptacles":

                    Index Isolated Ground 517.16 (section actually titled) "Use of Isolated Ground Receptacles"

                    However...

                    The term single point ground:

                    250.184 single point grounded
                    250.184(B) Single-Point Grounded Neutral System
                    250.184(B) Single-Point Grounded Neutral System
                    250.184(B)(1) Single-Point Grounded Neutral System
                    250.184(B)(1)b. Single-Point Grounded Neutral System

                    And "single point" where relevant to the discussion:
                    250.30(A)(1) single point

                    A complete Single Point grounding scheme is not fully (or even at all...) explained in the NEC.

                    Learning is for school. The NEC just gives us the minimum standards allowable for a "safe" installation (according to the insurance-industry-driven NFPA). There is a lot more to electrical theory, practice and the resultant installation than what is found in the NEC.

                    ...but I digress...

                    An isolated ground receptacle (250.146 (D)) means that the ground is not continuous to the mounting of the receptacle. It is literally isolated from the box and is not, when made fast, bonded nor continuous to the box, raceway, and all other items which are bonded...at that point. At the point where the grounds come together, the single point, is where the system is then made electrically safe and meets the intended need of the system in reducing noise or for other purposes as necessary.

                    A single point ground merely utilizes isolated ground receptacles to achieve the overall system isolation. This allows the boxes, raceways, etc. (exposed and available conductive parts) to be bonded for safety while allowing for the isolation and protection from EMF and other effects on the grounding conductor.

                    ...again, I digress...

                    In your example, when connected to multiple pieces of equipment on (in) a metal rack:

                    The power distribution unit (receptacle), surge suppressor, power strip, etc. is provided an isolated ground receptacle with a dedicated ground which is isolated from any and all bonded raceways, enclosures, building steel, counterpoises, etc. until it reaches either the main service or separately derived service, as applicable. Equipment racks (cabinets, housings, mountings, etc.) used isolated mounting hardware to keep it clear of stray connections to any bonded equipment. A grounding bar, also isolated from the cabinet except at one point (EGC/bonding conductor) is made fast and all EGC's for all rack mounted equipment are attached there. Equipment in the cabinet may also be provided with isolation mounts if necessary (i.e., excessive noise from a power supply at a nuisance frequency), but the EGC must be maintained. All grounding bars and plates for a particular system/installation/cabinet/rack/etc., as applicable must be bonded to the same service where power is derived...this is important for obvious (and NEC derived) reasons.

                    There is a lot more that goes into this, but the whole point is to properly understand and then make use of Kirchoff's observations and to keep circulating currents (EMF induced or vice-versa) whether power system or equipment derived from getting into areas which they is not desired (causing problems). There are endless types of "interference" and the resultant safe and legal methods which can be used to mitigate issues are simply the best way (cheap, easy, quick...pick two) of getting the job done.

                    The IEEE Green (Std 142), Emerald (Std 1100), Standard 3000, and Standard 3003 lay this all out nicely. The NEC and several other documents regularly reference (quoting and interpreting) these engineering standards which can also be directly referenced for exceptional installations of equipment with a very electro-sensitive nature.

                    This is not hypothesis, theory, conjecture, or some sort of hit-and-miss practice. These use of these (now considered) exceptions have a proper time and place for implementation. I agree that they can and have been abused, used as band-aids, and poorly implemented by many people, but that doesn't mean that each instance is nothing but hogwash.

                    I have personally been utilizing single-point grounding methods for nearly 30 years, building on knowledge and practice of over 100 years in my field alone.

                    Works fine...lasts a long time.
                    250.184 is in the section for over 1000 volts.

                    250.30 saying to connect the system bonding jumper to a single point in a separately derived system.

                    Service supplied systems are already grounded multiple times on the utility side if there is a grounded conductor because that is what POCO's do.
                    I live for today, I'm just a day behind.

                    Comment


                      #25
                      Originally posted by cuba_pete View Post
                      This is another case where the language and nomenclature used by the NEC, electricians, engineers, laymen, etc. gets confusing.

                      Of the 14 times that the term "isolated ground(ing)" appears in the 2014 NEC, almost exclusively followed by "receptacle".

                      Excerpted from the NEC:
                      250.96(B) Isolated Grounding Circuits
                      406.3(D) Isolated Grounding Conductor
                      406.3(D)(2) Exception: Isolated Ground Receptacle
                      517.16 Isolated Ground Receptacle
                      250.146(D) Isolated Ground Receptacles
                      406.3(D) Isolated Ground Receptacles
                      406.3(D)(2) Isolated Ground Receptacles
                      517.16 Isolated Ground Receptacles
                      640.7(C) Isolated Ground Receptacles
                      647.7(B) Isolated Ground Receptacles
                      647.7(B) Isolated Ground Receptacles
                      640.7(C) Isolated Grounding-type Receptacles
                      645.15 Informational Note No. 2: Isolated Grounding-type Receptacles
                      250.184(B) Single-Point Grounded Neutral System

                      Whereas the only time that the term "Isolated Ground" is found alone in the 2014 NEC is in the Index, and actually refers to section 517.16 which is, you guessed it, a section on "Use of Isolated Ground Receptacles":

                      Index Isolated Ground 517.16 (section actually titled) "Use of Isolated Ground Receptacles"

                      However...

                      The term single point ground:

                      250.184 single point grounded
                      250.184(B) Single-Point Grounded Neutral System
                      250.184(B) Single-Point Grounded Neutral System
                      250.184(B)(1) Single-Point Grounded Neutral System
                      250.184(B)(1)b. Single-Point Grounded Neutral System

                      And "single point" where relevant to the discussion:
                      250.30(A)(1) single point

                      A complete Single Point grounding scheme is not fully (or even at all...) explained in the NEC.

                      Learning is for school. The NEC just gives us the minimum standards allowable for a "safe" installation (according to the insurance-industry-driven NFPA). There is a lot more to electrical theory, practice and the resultant installation than what is found in the NEC.

                      ...but I digress...

                      An isolated ground receptacle (250.146 (D)) means that the ground is not continuous to the mounting of the receptacle. It is literally isolated from the box and is not, when made fast, bonded nor continuous to the box, raceway, and all other items which are bonded...at that point. At the point where the grounds come together, the single point, is where the system is then made electrically safe and meets the intended need of the system in reducing noise or for other purposes as necessary.

                      A single point ground merely utilizes isolated ground receptacles to achieve the overall system isolation. This allows the boxes, raceways, etc. (exposed and available conductive parts) to be bonded for safety while allowing for the isolation and protection from EMF and other effects on the grounding conductor.

                      ...again, I digress...

                      In your example, when connected to multiple pieces of equipment on (in) a metal rack:

                      The power distribution unit (receptacle), surge suppressor, power strip, etc. is provided an isolated ground receptacle with a dedicated ground which is isolated from any and all bonded raceways, enclosures, building steel, counterpoises, etc. until it reaches either the main service or separately derived service, as applicable. Equipment racks (cabinets, housings, mountings, etc.) used isolated mounting hardware to keep it clear of stray connections to any bonded equipment. A grounding bar, also isolated from the cabinet except at one point (EGC/bonding conductor) is made fast and all EGC's for all rack mounted equipment are attached there. Equipment in the cabinet may also be provided with isolation mounts if necessary (i.e., excessive noise from a power supply at a nuisance frequency), but the EGC must be maintained. All grounding bars and plates for a particular system/installation/cabinet/rack/etc., as applicable must be bonded to the same service where power is derived...this is important for obvious (and NEC derived) reasons.

                      There is a lot more that goes into this, but the whole point is to properly understand and then make use of Kirchoff's observations and to keep circulating currents (EMF induced or vice-versa) whether power system or equipment derived from getting into areas which they is not desired (causing problems). There are endless types of "interference" and the resultant safe and legal methods which can be used to mitigate issues are simply the best way (cheap, easy, quick...pick two) of getting the job done.

                      The IEEE Green (Std 142), Emerald (Std 1100), Standard 3000, and Standard 3003 lay this all out nicely. The NEC and several other documents regularly reference (quoting and interpreting) these engineering standards which can also be directly referenced for exceptional installations of equipment with a very electro-sensitive nature.

                      This is not hypothesis, theory, conjecture, or some sort of hit-and-miss practice. These use of these (now considered) exceptions have a proper time and place for implementation. I agree that they can and have been abused, used as band-aids, and poorly implemented by many people, but that doesn't mean that each instance is nothing but hogwash.

                      I have personally been utilizing single-point grounding methods for nearly 30 years, building on knowledge and practice of over 100 years in my field alone.

                      Works fine...lasts a long time.
                      So long long long post later you don't have an IG system in your lab.

                      Got it.

                      Comment


                        #26
                        Single point grounding is a term that has multiple meanings depending on who is using it....in the NEC it really just means that there is only one connection between the grounded and grounding conductors. That would be at the main bonding jumper for a service or the system bonding jumper for a SDS.
                        Don, Illinois
                        (All code citations are 2017 unless otherwise noted)

                        Comment


                          #27
                          Yeah, I got it.

                          My main point by providing the actual documentation in the NEC is that electricians who rely solely on the NEC won't learn anything about the true nature of, or how to implement single-point grounds, nor will they learn what an isolated ground is/isn't.

                          Trying to apply learned logic and reasoning with one publication that isn't a valid resource can be frustrating and will not provide proper results.
                          Kirchoff and Ohm...the only laws that make sense

                          Comment

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