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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.

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    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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  • 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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