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Case 2. C.P.C. corrosion in T&E cable.

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Today I stripped some 2.5mm2 T&E cables that run in 25mm black plastic conduit outside. The cable was continuous with no joints in the conduit boxes. The plastic conduit showed signs of being overheated in the sun at some period through the day. I had to cut the cable to make a joint, and I found that the C.P.C. showed signs of corrosion, just starting to show, nothing serious but enough to cause concern. I repeat, the cable had not been jointed when I found it and was continuous with the outer sheath intact throughout.


I can only conclude that the cables's outer sheath has let in moisture, even though the cables run in plastic conduit.


Is this why the Regs. do not advise running P.V.C. cables submerged in water? P.V.C. is not totally waterproof. 522.3.

https://www.belden.com/blog/broadcast/waterblocking


Z.

  • 0
    Agree - I have seen large SWA dragged through ornamental lakes and ponds just to get the length and cost down - they end up paying twice because it is not submarine cable and is not designed to be submerged for any length of time.

    SWA run outside is pretty much ok since the rainwater runs off it. But it was never designed to be run underwater.

    PVC T&E outside is just pants.

    Use NYY or SWA instead
  • 0

    whjohnson:

    Agree - I have seen large SWA dragged through ornamental lakes and ponds just to get the length and cost down - they end up paying twice because it is not submarine cable and is not designed to be submerged for any length of time.

    SWA run outside is pretty much ok since the rainwater runs off it. But it was never designed to be run underwater.

    PVC T&E outside is just pants.

    Use NYY or SWA instead




    What about running SWA underground? Isn't that wet?

  • 0

    Chris Pearson:




    whjohnson:

    Agree - I have seen large SWA dragged through ornamental lakes and ponds just to get the length and cost down - they end up paying twice because it is not submarine cable and is not designed to be submerged for any length of time.

    SWA run outside is pretty much ok since the rainwater runs off it. But it was never designed to be run underwater.

    PVC T&E outside is just pants.

    Use NYY or SWA instead




    What about running SWA underground? Isn't that wet?


     




    It certainly can be but at a guess, an in areas other than bogs, the water pressure should be much lower than if the cable was running at the bottom of a lake etc.

  • 0
    NYY cable looks tough for outdoor use. I would not bury it though as it has no earthed armouring. Normally P.V.C./P.V.C. cables seem to be o.k. run on brickwork if they have a chance to dry out after rain. I imagine that the cables in the plastic conduit that I discovered were subjected to a hot humid environment on occasions like in a sauna, which may have caused moisture ingress into the cable. The conduit had no drain holes at the lowest points.


    Z.
  • 0
    PVC and in fact most plastics  slightly porous to water, (not like a cloth, more like plywood is..) and they will reach some sort of very long term (many days) equilibrium with the surroundings. The rate of absorption by PVC seems to depends very much on the plasticizers used, and is much slower for hard PVC (like conduit, drain pipe etc.) than the flexible films.

    A sample of pure PVC will gain about 0.1% in weight after long term immersion and then being dried off and weighed - the water has burrowed in and is hidden in between the molecules.

    Polypropylene and polythene are much better materials in this regard- nylon and polystyrene are  a lot worse.

    table on page 5 is relevant.

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