About 30 years I was helping a mate move into his "new" house. I can't remember why I cut into what looked like a metal pipe or conduit, but I did. It was not flexible. Inside were 3 bare wires, no insulation but the pipe/conduit was packed full of white powder. I'd never seen this before, neither had the owner of the electrical shop. Has anybody any idea what this thing was?
Sounds like bog standard MICC cable.
Philip
Mineral insulated cable, AKA Pyro?
some of us would use a proper ringing tool
A nasty festered rubber coated old mains supply perished to heck.
Either that or a very long bbig fuse!! Brian
What was the diameter of the "pipe"?
(although it sounds like MICC, that is quite narrow in most commonly used domestic sizes).
Maybe half inch.
No sheath, the wires just seemed to be somehow kept apart by the powder.
Cheers for that Harry, I now sort of understand. How the hell did they get the wires into the tube without them making contact with each other?
I don't know how they make it either, but I suspect that, like seaside rock, it starts off shorter and fatter, and is then drawn through a die. Maybe hot, maybe cold? The friction between the ceramic insulator particles will stop anything from moving about radially, and will transmit the axial strain from the drawing process through to the wires.
Long plastic pipe, on the other hand, is extruded hot through a die. The bore is formed by a bullet-like object located centrally by three spider legs, the slits left by them close up as the material solidifies. You can see the witness marks on ABS tube.
That would be a fairly hefty cable - perhaps 2 x 10mm^2 (and you get more current for your square mm in MICC since it can run hotter)
There is a table of common sizes here:
I think that Harry has enlightened me, thanks for your help. What the hell was this sort of stuff doing under the floor boards of a bungalow?
After 30 years who knows?
Feeding a garage? It may have gone outside further down the run.
It may not have been not use. Did it go bang when you cut it? Maybe an old feed from when it was a building site.
I think it may have been feeding the garage as I was putting lights in the garage. I can't remember why I cut it, maybe to rewire the cable to the garage, which I did.
I had all the power turned off.
Do you often cut 'pipes' without knowing what they do?
Inside were 3 bare wires, no insulation but
Are shops a good source of advice? I went into Asda and the girl on the till hadn't a clue about how to work the camera I bought from there 15 years earlier.
MICC cable aka "Mineral Insulated" or "Pyro".
The powder is Magnesium Oxide (I think) - it is packed in as part of the drawing process - literally the "wires" star off as copper rods in a big copper tube, add powder, draw the whole lot out to the required thickness, rods and all.
It comes in pretty long lengths. I've always wondered how it starts out, and what sort of machinery is used to "draw" it. Wikipedia says it is reduced using rollers which I guess makes sense.
Just for info to others who may not have come across it, thermocouples clad in stainless steel tube are essentially the same technology. So are the heating elements in electric ovens. I've made up "custom" heaters in the past using nichrome clad in stainless steel. You terminate by removing a suitable length of sheath, brazing a "nipple" to the sheath, and sealing the exposed magnesium oxide insulation by fusing glass powder into a cup on the nipple. If you don't do this, moisture gets into the insulation and you lose insulation resistance.
Close, but it is rolled, rather than drawn.
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