What would this cable have been for? 3

[swazimatt]

Working on a sit that used to be a work camp in the 40’s and have come across these cables. Two copper cables about 3mm diameter surrounded by some sort of cement(?) all within a copper sleeve.
I am a civil engineer so forgive me if this is obvious. Also not sure what the purpose of the copper outer sleeve was for

 

[LittleInch]

Looks very much like MICC cable.

Mineral-insulated copper-clad cable - Wikipedia

en.m.wikipedia.org

So for protection or sensitive signals.

 

[waross]

Pyrotenax Mineral insulated cables.
The "some kind of cement' is magnesium dioxide.
The cables were almost indestructible.
The enclosed heating elements (Not the exposed spiral nichrome elements)in your oven and stove top elements are often a similar construction, that is insulated with magnesium dioxide.
The magnesium dioxide would absorb water if the cable end was left open.
When terminating MI (Mineral Insulated) or Pyrotenax (Trade name) it was common practice to heat the last foot or so of the cable with a torch to force any moisture out.
There were termination kits that sealed the ends of the cable after it had been cut to length.
I remember seeing the following warning on one termination kit.
CAUTION
IF HEAT IS APPLIED TO DRY THE CABLE,
CARE MUST BE TAKEN THAT THE COPPER
IS NOT MELTED.
That was the maximum peak allowable temperature, just below the melting point of copper.
Years ago,gasoline pumps were wired in threaded rigid conduit.
It took a lot of skill to cut and thread the various pieces of conduit to exactly the correct length.
A sealing fitting had to be included in the piping arrangement.
Then Pyrotenax kits became available for wiring gas pumps.
The cable had the correct number of conductors for a standard gas pump.
The cable was explosion proof.
The cable was inherently sealed and there was no need for a separate sealing fitting to be added.
The required skill level to install was much less than it had been for conduit installations.
Pyrotenax is used for fire critical installations and for high temperature applications.
The last time I used Pyrotenax was to supply the fan motors in a softwood lumber kiln.
The kilns were heated with superheated steam and the ambient temperature could exceed the boiling point of water.
One one run I recorded a peak temperature of 230 degrees F on the fan deck.

 

[waross]

The construction of the cable started with stout copper bars placed inside a stout copper cylinder and the voids between the bars and the cylinder was filled with magnesium dioxide powder.
The assembly was then drawn through ever reducing dies until the combination of the desired length and desired diameters was achieved.

 

[swazimatt]

Thanks for the replies.
So this was a predecessor to armour cable in this application? Buried power supply? Considering this was a government work camp so temporary housing

What era would this have normally been used?
This is in Tokoroa NZ

 

[waross]

WIKI QUOTES:

WIKI

History​

The first patent for MI cable was issued to the Swiss inventor Arnold Francois Borel in 1896. Initially the insulating mineral was described in the patent application as pulverised glass, silicious stones, or asbestos, in powdered form. Much development ensued by the French company Société Alsacienne de Construction Mécanique.[1] Commercial production began in 1932 and much mineral-insulated cable was used on ships such as the Normandie and oil tankers, and in such critical applications as the Louvre museum. In 1937 a British company Pyrotenax, having purchased patent rights to the product from the French company, began production. During the Second World War much of the company's product was used in military equipment. The company floated on the stock exchange in 1954.[2]

WIKI

History​

The first patent for MI cable was issued to the Swiss inventor Arnold Francois Borel in 1896. Initially the insulating mineral was described in the patent application as pulverised glass, silicious stones, or asbestos, in powdered form. Much development ensued by the French company Société Alsacienne de Construction Mécanique.[1] Commercial production began in 1932 and much mineral-insulated cable was used on ships such as the Normandie and oil tankers, and in such critical applications as the Louvre museum. In 1937 a British company Pyrotenax, having purchased patent rights to the product from the French company, began production. During the Second World War much of the company's product was used in military equipment. The company floated on the stock exchange in 1954.[2]

 

[LittleInch]

Not really armoured cable but more fire resistant cable, especially at the size you have there.

 

[waross]

Of course the cable could be cut, but it could not be shorted by blunt force trauma.
The first time that I encountered Pyro' the old UK electricians installing it claimed that the Pyrotenax company had done a demonstration by throughing a Pyro' cable carrying 100 Amps across the tracks at the busiest rail junction in England.
They claimed that after a day of being run over by trains, the cable was still carrying 100 Amps and was not shorted out.
And, I mis-spoke.

magnesium dioxide powder

Should have been;
"magnesium oxide"