Forums » Electrical Engineering

11kV Triplex Cables

    • 27 posts
    February 7, 2019 11:21 PM PST

    Good afternoon. 11kV Triplex Cables Terminated Onto Switchgear Bushings Using Heat Shrink Cable Terminations

    what is the purpose of the black wires?


    photo source:

    • 7 posts
    February 8, 2019 6:13 AM PST
    11Kv and seeing those black wires joined to a common busbar with a green/ yellow,I assume earth ground, is scary to me! I don’t know why that shielding is present if that is what the picture is showing me?
    • 156 posts
    February 8, 2019 8:58 AM PST

    I think, this is the point MV cable earth screen grounding. So, the earth screen MV cable should be grounded at both end. 

  • February 8, 2019 11:20 AM PST

    Yes, as Hameed said, it is shielded cable..  The OP pic shows the outside of the stress cone.  The black wire is connected to the (usually copper foil) shield around the outside of the insulation.  The drain is always connected on one end, not always on both ends.

    I'm out of my area of expertise on the physics.  (That translates to, "I telling you more than I know")  The cable insulation is a dielectric - not non-conductive.  My understanding is this keeps the stress fields even so the insulation does not break down.  The shield is required to bring the outside surface of the insulation down to ground (earth) potential.  The shields have to be earthed (grounded)

    I attached a couple of pictures showing the insides




    Here is a link to an MV terminating guide.

    3m splicing guide

    This post was edited by Deleted Member at February 8, 2019 11:26 AM PST
    • 156 posts
    February 8, 2019 11:41 AM PST

    Yes, Carl is correct. It is not necessary always to ground it at both side. for determining the size of earth screen also one should suppose the worse case as one side grounding.

    I found another photo for this


    • 27 posts
    February 8, 2019 12:23 PM PST

    Thank you