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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The cable is out of date but appears to be still serviceable.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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    Legh Richardson:




    The quality of both the insulation and cloth covering at and around the terminals is still flexible as there is quite a bit of spare left in a rather large galvanized switch fused enclosure. That surplus allowed me to take a biopsy! .the cable available to be viewed appears to be healthy for its age; I can't say what the quality is within the conduit but as Zoom has stated it has its own protected micro climate.

    Legh




     




    Legh, the enemy of this cable (and any others) is heat, caused by loose connections or the cyclic nature of the load, causing expansion and contraction at screw terminals, the connections at sockets etc. are then vulnerable. If not checked at routine intervals and tightened when loosened, you get an escalating resistance effect. VRI cable insulation is particularly vulnerable to embrittlement, as you know. It is probably OK inside conduit, provided it is not subject to a heat causing, chimney effect. 


    Jaymack  

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  • 0

    Legh Richardson:




    The quality of both the insulation and cloth covering at and around the terminals is still flexible as there is quite a bit of spare left in a rather large galvanized switch fused enclosure. That surplus allowed me to take a biopsy! .the cable available to be viewed appears to be healthy for its age; I can't say what the quality is within the conduit but as Zoom has stated it has its own protected micro climate.

    Legh




     




    Legh, the enemy of this cable (and any others) is heat, caused by loose connections or the cyclic nature of the load, causing expansion and contraction at screw terminals, the connections at sockets etc. are then vulnerable. If not checked at routine intervals and tightened when loosened, you get an escalating resistance effect. VRI cable insulation is particularly vulnerable to embrittlement, as you know. It is probably OK inside conduit, provided it is not subject to a heat causing, chimney effect. 


    Jaymack  

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