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rubber insulated cloth covered tinned copper submain cable in galv. conduit.

Legh Richardson
Had a look at an installation which has a submain running approximately 25m to supply a kitchen.

We thought umm this looks interesting, cut a slice off at the output of the switched fuse and re-terminated. The cloth, and rubber appears to be in reasonable condition for what appears to be nearly 70 years old. An insulation test at 500V gave a reasonable result (>500M) and a leakage test gave the same, 0.41mA.

The cable is out of date but appears to be still serviceable. It is not heavily used and the ambient temperature is generally quite low. I think I might advise that the cable is replaced by a newer edition or at least regularly checked every year. Has anybody got any other ideas?


Legh
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    Old rubber insulated cable, including cotton covered or rubber insulated in a lead sheath, lasts for many years. This cable in a conduit is similar in that it exists in its own protective "micro climate". It is normally at the ends that changes of temperature and humidity cause rubber deterioration. I have seen just the ends of such cable oversleeved with P.V.C. sleeving after just the ends deteriorated. I inspected a house in Sheringham a few years ago, and the main runs of the old rubber insulated cables were in a remarkably good condition considering that they were probably installed in the 1040s/50s. They were still flexible and the insulation resistance was very high. The rubber insulation was remarkably think. The old boy owner would not have a rewire, all I could do was to improve the earthing for safety.


    Z.
Reply
  • 0
    Old rubber insulated cable, including cotton covered or rubber insulated in a lead sheath, lasts for many years. This cable in a conduit is similar in that it exists in its own protective "micro climate". It is normally at the ends that changes of temperature and humidity cause rubber deterioration. I have seen just the ends of such cable oversleeved with P.V.C. sleeving after just the ends deteriorated. I inspected a house in Sheringham a few years ago, and the main runs of the old rubber insulated cables were in a remarkably good condition considering that they were probably installed in the 1040s/50s. They were still flexible and the insulation resistance was very high. The rubber insulation was remarkably think. The old boy owner would not have a rewire, all I could do was to improve the earthing for safety.


    Z.
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