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.
