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Strange C.P.C. attack and size reduction.

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Evenin' all,

                         today I attended a shop store at a beach location. The store is on the prom just above high water level.


I decided to replace a double socket with rusty screws that the owner has suspicions about. The socket is wired in old 2.5/1.0mm2 T&E copper cable. There were three 2.5s connected at the socket, a ring pair and a spur. The live of the spur cable was blackened at the point where the sheath had been removed. The copper C.P.C. of the spur cable immediately snapped off when I moved it. It was discoloured and pitted along its length, but the weird thing is that its diameter reduced, pretty much consistently, the closer the C.P.C. was to the remaining sheath. When removed, the copper C.P.C. resembled a needle, tapering down in diameter towards the place where it broke off at the point of sheath removal. Was this due to historical tracking between live and C.P.C? Or was it electrochemical corrosion and weird physics? The damaged length was about 50mm long,


Z.


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  • 0
    I don't recall ever seeing a tapering effect on any cable. Generally if salt water had got in a junction box, ite would be a corroded mess.  The only odd corrosion that I recall was on a Stern Light (a small white light on the stern) not a high wattage. A quick Googles tells me that a stern light needs to be visible at 3 miles (in the dark!).  Anyway, this particular junction had different corrosion on each of the two terminals: one terminal was black, the other not, even though an a.c. supply.  ISTR that I put it down to the earth monitoring system impressing low voltage DC onto the system, and thus the cause of the differing corrosion was from that DC.  Incidentally, I recall that the red line on the earth leakage meter for the 220 v 60Hz domestic (including nav lights) was 220 k ohm basically 1 mA per volt. 

    Clive
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  • 0
    I don't recall ever seeing a tapering effect on any cable. Generally if salt water had got in a junction box, ite would be a corroded mess.  The only odd corrosion that I recall was on a Stern Light (a small white light on the stern) not a high wattage. A quick Googles tells me that a stern light needs to be visible at 3 miles (in the dark!).  Anyway, this particular junction had different corrosion on each of the two terminals: one terminal was black, the other not, even though an a.c. supply.  ISTR that I put it down to the earth monitoring system impressing low voltage DC onto the system, and thus the cause of the differing corrosion was from that DC.  Incidentally, I recall that the red line on the earth leakage meter for the 220 v 60Hz domestic (including nav lights) was 220 k ohm basically 1 mA per volt. 

    Clive
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