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    Megger or Replace cable

    Hi folks,

    We're replacing a low voltage air compressor that has been in service for around 50 years at an industrial plant. Would you recommend megger testing the feed or pulling a new cable? The distance is about 70 feet from MCC to the unit.

    Thanks,
    EE

    #2
    Originally posted by FaradayFF View Post
    Hi folks,

    We're replacing a low voltage air compressor that has been in service for around 50 years at an industrial plant. Would you recommend megger testing the feed or pulling a new cable? The distance is about 70 feet from MCC to the unit.
    My gut says replace it but you will need to do a cost benefit analysis to get a definitive answer that question i.e. [cost to replace cable] vs. [cost to test cable] + [cost to replace cable] x odds it has failed stated as a decimal from .00 to 1.00.

    Make sure you take all the labor and material costs into account for an accurate analysis. (Including the difficulty of running the cable.)

    You could also do nothing and replace it when it fails. This might be the least expensive solution if downtime is allowed.

    Comment


      #3
      We did a sound analysis of feeders for some pellet mills. I had the CEO listen as I bent the wires in a gutter. The sound of the old rubber insulation cracking was enough. It most likely would have passed a megger test as the area was dry and they had had no issues.
      Tom
      TBLO

      Comment


        #4
        Originally posted by ptonsparky View Post
        I had the CEO listen as I bent the wires in a gutter. The sound of the old rubber insulation cracking was enough. It most likely would have passed a megger test as the area was dry and they had had no issues.
        And they might meg out fine until they're being bent around to connect the new compressor. If it's a fairly easy pull, I'd just replace them.

        What size are we talking about? Heck of a difference between replacing 10g and 2g.

        Comment


          #5
          In a nuke you megger new wire.

          Comment


            #6
            Originally posted by sameguy View Post
            In a nuke you megger new wire.
            Not only nukes. I've seen many new switchgear installs get megged. Last thing you want is all that new equipment blowing up due to a bad conductor.

            Comment


              #7
              Originally posted by Coppersmith View Post
              Not only nukes. I've seen many new switchgear installs get megged. Last thing you want is all that new equipment blowing up due to a bad conductor.
              It is in our spec to meg all new circuit conductors--Done that all my career--just makes sense--only takes seconds to meg a conductor
              RichB N7NEC

              Comment


                #8
                Originally posted by FaradayFF View Post
                Hi folks,

                We're replacing a low voltage air compressor that has been in service for around 50 years at an industrial plant. Would you recommend megger testing the feed or pulling a new cable? The distance is about 70 feet from MCC to the unit.

                Thanks,
                EE
                Define low voltage. What HP?
                Tom
                TBLO

                Comment


                  #9
                  20 HP unit.

                  Comment


                    #10
                    Originally posted by FaradayFF View Post
                    20 HP unit.
                    That's #8 at 480v. It cost more to talk about it than pull new wire. Depending on what your work procedures are, of course. Is there easily scheduled down time?
                    Tom
                    TBLO

                    Comment


                      #11
                      pt -
                      Yep, and #10CU are enough

                      20HP
                      27A x 1.25 = 34A
                      310.15.b >> #10CU, 75C >> 35A
                      Without data you’re just another person with an opinion – Edwards Deming

                      Comment


                        #12
                        Well,

                        These are actually 208Volts motors. The cables are installed in a dry environment, so I think we'll just end up megger them.

                        Thanks to all who responded.

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