Discuss Old cable in dwelling light circuit in the Electrical Forum area at ElectriciansForums.net

Lucien Nunes

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Was the lead covered flat cable used at the same time as vir singles? I've never seen it terminated.

Generally yes, but lead fell out of use earlier. Where cost was the main consideration, TRS was cheaper than lead and increasingly found acceptance for domestic work. Where durability was the main consideration, VIR in conduit had always been and remained the system of choice. TRS was superseded by PE/PVC T+E, VIR singles by PVC singles. Lead sheaths kind-of fell through the gap in the middle for building installations, although continued to offer advantages for underground cables.

Lead twin was normally jointed using pressed metal JBs with screw-down clamping bars at the cable entries to connect the sheath to the box. At fittings such as roses and switch pattresses, continuity could be maintained and/or a connection could be picked up off the sheath using screw-on clips, or by pairs of flat bars that could be clamped around multiple cables. These were called 'bonding bars' because at that time 'bonding' meant maintaining earth continuity generally, rather than specifically connecting extraneous conductors to the equipotential. For ironclad fittings and switchgear there were saddle-type clamps that screwed into the conduit entries.

Because lead flows easily, these various clamping methods did not remain very tight. Although continuity was normally maintained, it was recognised as a weak spot and for high-class lead work even by the early '30s there was the option of lead twin with a bare tinned copper CPC inside, in contact with the sheath. This was terminated in the JB in the usual way offering a reliable CPC connection to both the sheath and the next point.
 
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The most common borrowed neutral situation is a single core live taken from the downstairs lighting circuit to the 2 way switch at the bottom of the stairs. Then a twin is taken from downstairs switch to upstairs switch and another single, the switched live, taken from their to the light above the stairs. This light would then have its neutral connected to the upstairs lighting circuit. Thus the two circuits become linked, and quite dangerous for anyone working on it.
This is precisely what has been done, although it is initiates im the downstairs hallway which is also controlled by a 2 way switch. It is such a mess. I’ve also noticed that at every junction box the installer has simply twisted the individual CPC together at the back of each box. Whilst it’s not necessary dangerous as such, it is bad/lazy practice. Indeed at 2 junction box on the final ring, the CPC has separated. I’ve replaced each junction box with new Wago box and connected the CPC securely. It really is quite a mess.
 

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