Weird 70's installation

Postby nerd8192 » Sat Jul 25, 2009 4:09 am

I wonder if anyone has ever come across wiring like this, which basically consists of a copper rod in the wall/ceiling, then capped with a brass cap and some black goo at the point where it is to be connected to socket/switch/rose. This is in a flat built in 1972 with shuttered concrete walls.


I was replacing a light switch when suddenly the wire broke off from the brass cap and I am left with only one wire to my switch! Need to find a way to fix this, hopefully without running a new switch cable - mainly because it is complicated enough as it is.

At the rose end, where I have disconnected the switch wire, I have no clue which is live/neutral/earth and only one wire is live (as tested with a voltfinder once power was re-applied). Most wires are sheathed with black or green insulation, but I am pretty sure most of the green ones aren't earth!

Thanks for your help,

Preston, Lancs
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Joined: Sat Jul 25, 2009 4:02 am


Simply Build It

Postby rosebery » Sat Jul 25, 2009 9:32 am

Link no workee old son.

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Postby sparx » Sat Jul 25, 2009 9:35 pm

Hi you are talking about mineral insulated copper covered cable known as 'Pyro', if you have broken a core you have a serious problem!
The cable is made up of a copper outer sheath (tube) with hard drawn bare copper cores inside with a white powder (no not that one)magnesium oxide, insulator,
the termination consists of a 'pot' which is screwed onto the copper sheath after a length has been removed to expose inner cores for connection, insulation sleeving and a seal are threaded over cores and a sealing compound is inserted into the pot and then sleeving/seal are slid into pot and crimped in place with a special tool.
The outer copper tube is used for circuit earth and the cores have to be tested and marked for use ie Line or neutral, at switch both sleeves should be marked with red over sleeve to indicate live/switch line.
Repairing damaged cable will need experienced, probably older leckie since most don't have tools/knowledge to work on mics cables, also by age cable/pots will be old 'imperial' sizes and no longer available.
Which is why I and hopefully other old geezers keep some in stock!
good luck finding someone in your area, I'm on South Kent coast......
don't travel off Romney Marshes,
regards Sparx

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Location: The fifth continent.

Postby nerd8192 » Mon Jul 27, 2009 9:35 pm

Hi Sparx,

I think that I am dealing with pyro, thanks for your help.

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Joined: Sat Jul 25, 2009 4:02 am

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