Announcement

Collapse
No announcement yet.

Ground wire in MC cable

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Ground wire in MC cable

    Why is the ground wire in MC cable insulated? I feel like its more cost without anything in return so I'm guessing their must be a reason.

    #2
    Tradition!

    Presumably buried somewhere in the UL requirements.

    Actually the ground wire in 'MC-AP' is non-insulated aluminium, and placed outside of the wrap that protects the other conductors, so that it is in contact with the spiral sheath. So you get a cheaper aluminium conductor that lets you use the sheath as the EGC. The 'full size' aluminium conductor is roughly the same size as the insulated copper conductors, so everything falls together pretty nicely.

    -Jon

    Comment


      #3
      We talked about redesigning NM to have an insulated ground.

      Uninsulated EGCs in boxes are a never ending problem, especially now with AFCI and GFCI breakers that readily show up the problem of an EGC contacting the neutral if someone is not very careful installing devices.

      Also, unlike NM, MC is likely to be used at higher voltages in commercial installations, so a bare EGC floating around in device boxes is asking for trouble.

      So, really, an insulated EGC in NM equals higher quality and a safer, more trouble free installation IMO.

      As far as MC-AP, as far as I'm concerned it should be considered type AC. MC was never allowed to use the armor as an EGC and unless the ground wire is required to be brought into the box and bonded to the box with a ground screw, I don't see the difference between it and AC. They both rely on just the box clamp to armor to provide the ground bond. I'm thinking the NEC caved to some manufacturer once again.

      -Hal

      Comment


        #4
        Originally posted by hbiss View Post
        We talked about redesigning NM to have an insulated ground.
        Missed it. Is there a thread?

        Uninsulated EGCs in boxes are a never ending problem, especially now with AFCI and GFCI breakers that readily show up the problem of an EGC contacting the neutral if someone is not very careful installing devices.

        Also, unlike NM, MC is likely to be used at higher voltages in commercial installations, so a bare EGC floating around in device boxes is asking for trouble.

        So, really, an insulated EGC in NM equals higher quality and a safer, more trouble free installation IMO.



        -Hal

        Can I be honest? I always thought a bare EGC was cheesey, even thought that code should mandate insulation- though not without getting some vocal critiques.



        As far as MC-AP, as far as I'm concerned it should be considered type AC. MC was never allowed to use the armor as an EGC and unless the ground wire is required to be brought into the box and bonded to the box with a ground screw, I don't see the difference between it and AC. They both rely on just the box clamp to armor to provide the ground bond. I'm thinking the NEC caved to some manufacturer once again.

        Exactly! I am in full agreement here. To me MC without a dedicated ECG is simply AC cable.

        Comment


          #5
          Originally posted by hbiss View Post
          We talked about redesigning NM to have an insulated ground.

          Uninsulated EGCs in boxes are a never ending problem, especially now with AFCI and GFCI breakers that readily show up the problem of an EGC contacting the neutral if someone is not very careful installing devices.

          Also, unlike NM, MC is likely to be used at higher voltages in commercial installations, so a bare EGC floating around in device boxes is asking for trouble.

          So, really, an insulated EGC in NM equals higher quality and a safer, more trouble free installation IMO.

          As far as MC-AP, as far as I'm concerned it should be considered type AC. MC was never allowed to use the armor as an EGC and unless the ground wire is required to be brought into the box and bonded to the box with a ground screw, I don't see the difference between it and AC. They both rely on just the box clamp to armor to provide the ground bond. I'm thinking the NEC caved to some manufacturer once again.

          -Hal
          Finally someone else has spoken up about the problems with with a uninsulated bond wire that I been thinking about for yes.

          Especially now with trying to install a AFCI brk on a existing circuit you are trying to meet code with remodelling work amongst other things.

          I couldn't agree more.

          Comment


            #6
            Years, Not yes.

            Comment


              #7
              Originally posted by mbrooke View Post

              Missed it. Is there a thread?
              Ah, it was in one of those rants about AFCIs where we got to thinking about making wiring safer to begin with. No idea which one. Wasn't much more said than what I said here anyway.

              -Hal

              Comment


                #8
                probably because whoever wrote the UL specs for MC decided it was a good idea. Lots of things happen that way. Or maybe so it can be buried.
                Bob

                Comment


                  #9
                  Or maybe it was done that way since they decided to add an EGC to NM way back in, what, the 30's? Why change it now?

                  -Hal

                  Comment


                    #10
                    JMHO, it all comes down to a fault path>

                    ~RJ~

                    Comment


                      #11
                      Originally posted by romex jockey View Post
                      JMHO, it all comes down to a fault path>

                      ~RJ~
                      But a bare EGC wouldn't make a difference, right?

                      Comment


                        #12
                        Right. An insulated or bare EGC in itself doesn't make a difference as far as being able to carry a fault current and trip the breaker, sizes being equal.

                        The difference above with HCF vs MC is that HCF provides a redundant EGC using the armor plus a separate EGC run with the other conductors. MC is prohibited from using its armor as an EGC and has a separate EGC run with its other conductors.

                        Now they have MC-AP that has a full size bonding conductor under the armor allowing the armor to be used as an EGC. Like AC, there is no separate green grounding conductor. Only difference between it and AC is that there is no paper wrapping under the armor. Might as well call it MC-AC

                        -Hal
                        Last edited by hbiss; 10-08-19, 02:43 AM.

                        Comment


                          #13
                          One thing that makes MC-AP closer to normal MC than to AC is that that the full size ground conductor _may_ be used as a wire EGC in the same fashion as the green insulated EGC in normal MC.

                          MC-AP is _marketed_ and generally intended to be used where you cut the EGC wire short and use the connection to the sheath via to cable clamp as the EGC. Essentially exactly the way AC gets used. However you are _permitted_ to bring the wire into the enclosure and splice just like any other wire EGC...except that your splice needs to be suitable for aluminium conductors.....


                          -Jon

                          Comment


                            #14
                            And two AWG sizes smaller? I don't know of any connector that takes less than 12 AWG aluminum.

                            Comment


                              #15
                              How's this for a guess, the cable was originally designed for pools where an insulated EGC was required and MC was easier to run than a metallic raceway. Of course this has changed.
                              Rob

                              Moderator

                              All responses based on the 2017 NEC unless otherwise noted

                              Comment

                              Working...
                              X