Identify rubbery cable insulation: Need to replace?

Oct 10, 2005 7 Replies
M

Hello,



I am just about to replace a 2 fused CUs with a single split-load MCB CU in order to make capacity for a new Cooker circuit.



House is mid 1960s with PVC insulation, steel (I think) conductors (multistrand earth). The cable seems fine and the insulation is intact wherever I have seen it, so I am thinking it doesn't need to be replaced. All I am planing on doing is sheathing the bare earth conductors. Does anyone disagree?



However, I have found 1 section in the ring main which appears to have black/red rubber insulation inside grey PVC sheath. Again, conductors appear to be steel. Did that exist? I thought rubber insulated cable tended to have rubber black sheath too. The 'rubber' insulation isn't degraded. It is still soft and flexible which makes me think that it isn't actually rubber, but it certainly feels rubbery and looks very different to the PVC elsewhere.



Does anyone have any ideas as to what this section of cable is? Does it need replacing? It is in a room I have already decorated, so I would rather not if there is not a good reason.



Thanks



Mark


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D

The conductors will be tin plated copper - not steel. Steel is a poor conductor and would need very large cables to be any use.

I'd be more concerned about the lack of earth on the lighting circuit.

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M

Probably tinned copper, not steel.

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C

Not if you've inspected it carefully.

What makes you think they're rubber? I've never heard of the two materials being mixed like this.

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M

Nor have I. But it strike me as probably perfectly possible. (theres lawyer talk.) Hybrids crop up occasionally at changeover times.

I'd inspect it carefully, and if its ok, its ok. How to rate it, as per rubber or as per pvc? I guess rubber.

NT

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M

Thanks

The insulation on the conductors of this 1 piece of cable (from the CU to first socket) is different. Much larger external diameterfor the same size of conductor, matt rather than gloss surface, feels rubbery to the touch and has writing on it (Made in England, I think). Unlike any PVC insulation I've seen, and unlike the PVC in all the other cables in the house.

I know it sounds strange, that's why I'm asking.

M
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A

Lead sheathed looks just like grey PVC. Lead sheathed rubber was quite common. It won't have an earth wire -- the lead sheath is the earth.

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C

Yes, it might if you don't touch or handle it or look at it very closely.

But not perhaps in the mid '60s (see OP).

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