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    Code in your area? "grounds"

    Is it now a requirement in your area to pull separate grounding conductors through all conduits, including rigid metal pipe, IMC, EMT, and ofcourse PVC.

    How about metalic sheathed cables, do they require bonding bushings with attached lugs to conect and bond the sheath of the cable with the rest of an installation? If so at both ends?

    Most installations that use metalic conduits have no ground wire pulled through, since metal is a good conductor and could be used as the grounding conductor. Today, practices are changing and much work is being done with a seperate grounding conductor pulled in addition to the conductive properties of the conduits being used as mechanical protection.

    What is the practice that are being used in your area, and what is required by code?

    Grounding theory often confuses me, in regards to safety purposes, for it is supposed to provide protection from personal injury and damage to property.
    But when you get into fault currents, which can be a much higher magnitude of the regular circuit conductors capacity, it is almost impracticable to size grounds to safely handle such currents.

    It is undertstood that overcurrent protection, such as fuses and breakers help with this issue, but when is it determined safe enough?

    Under a specific ammount of time.
    Ive been shocked before multible times but never carried a full fault current through my body that I know of.

    What is would be the effect of a person being in contact of a grounding wire during a fault?

    #2
    What is would be the effect of a person being in contact of a grounding wire during a fault?
    If the grounding wire that the person is touching is the one that is carrying the fault current, he will be subjected to a voltage to earth that is equal to the voltage drop on the EGC. Under fault conditions, this voltage may often be greater than 40 volts. If he is touching a grounding conductor that is not the one clearing the fault, he will be subjected to a voltage that is equal to the votlage drop on the grounded conductor between the main bonding jumper and XO of the utility transformer. This votlage drop should be much less than that on the EGC itself. Note that this second voltage will be on all conductive objects that are connected to the electrical grounding system. These voltages will be there until the OCPD acts to open the circuit.
    Don
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

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      #3
      But when you get into fault currents, which can be a much higher magnitude of the regular circuit conductors capacity, it is almost impracticable to size grounds to safely handle such currents.
      Not really. They only have to handle the current for a very short time if the OCPD is doing its job. An insulated copper conductor can handle 1 amp for each 42.25 circular mils of area for 5 seconds. For example #14 has an area of 4110 circular mils and can carry 97.31 amps for 5 seconds. Now 5 seconds is much longer than the trip time of a properly selected OCPD, so we need to convert this to "amperes squared seconds". 97.31 x 97.31 x 5 =47,346 amperes squared seconds. You divide this number by the expected clearing time of the OCPD to find out how much current the conductor can withstand. If the OCPD has a clearing time of 3 cycles (0.05 seconds) than the #14 can withstand 973 amps without damge for 3 cycles. (take the square root of 47346/0.05 to get this number).
      This Bussmann document does a much better job of showing this than I did.
      Don
      Don, Illinois
      (All code citations are 2017 unless otherwise noted)

      Comment


        #4
        Brightidea, welcome to the forum.

        I don't suppose you could fill us in on some of your background? "Electrician" is a broad term. I am a residential electrician who recently broke into commercial. Most of my practical experience is with romex, and for the past two months I've been learning to bend pipe.
        Originally posted by brightidea
        Is it now a requirement in your area to pull separate grounding conductors through all conduits, including rigid metal pipe, IMC, EMT...
        No, according to 250.118 (2), (3) and (4), IMC, RMC, and EMT are still valid types of equipment grounding conductors. However, a conductor is generally pulled inside these conduits in practice in my area.

        How about metalic sheathed cables, do they require bonding bushings with attached lugs to conect and bond the sheath of the cable with the rest of an installation? If so at both ends?
        No, according to the UL White Book, page 177 (pdf 215):
        Also, I don't believe bonding bushings are available for MC connectors, but I could be mistaken. I don't see how you could install one on a regular snap-in 3/8" connector.

        Comment


          #5
          Originally posted by brightidea
          Is it now a requirement in your area to pull separate grounding conductors through all conduits, including rigid metal pipe, IMC, EMT, and ofcourse PVC.

          I can't answer this question, but I can, I hope, help to explain it. From my years living in Chicago, I recall (and I might be completely wrong about this) that the Chicago Electrical Code includes the requirement that an EGC be pulled, even if the conduit is metallic. I hope someone from that area will affirm or refute that old memory of mine.

          Is that what your are asking, about whether other local areas have similar requirements?
          Charles E. Beck, P.E., Seattle
          Comments based on 2017 NEC unless otherwise noted.

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            #6

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              #7
              My entire life revolves around electricity; I eat sleep breath and talk electricity.
              Well then, you've come to the right place.

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                #8
                Welcome aboard. I joined this forum a couple of months ago, and it has been great.

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                  #9
                  Again thank you for your replies and most importanlty your help.

                  bright idea

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                    #10
                    This is a fantastic tool for all of us to improve our knowledge of our chosen feild. I just joined myself, and have certainly learned a few things! I am always aware that I still have a lot to learn. I hope to improve myself professionally, which would certainly translate to improving myself as a person. I'm certainly going to keep coming back!
                    John from Baltimore "One Day at a Time"

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                      #11
                      BightIdea, you stated that:
                      Is it now a requirement in your area to pull separate grounding conductors through all conduits, including rigid metal pipe, IMC, EMT, and ofcourse PVC.

                      You are aware that a EGC is not required for IMC and RMC in the NEC. The IMC and RMC is itself allowed as an EGC. If an EGC is required, then its a workmanship issue on the IMC and RMC installation, per the CMP. I personally want to see an EGC in all raceways.
                      Moderator-Washington State
                      Ancora Imparo

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