Electric wires in conduit?

especially small copper pipes

I went to the factory maybe fifty years ago. The assembly starts off as a copper tube maybe 100mm diameter and copper rods maybe 25mm diameter inside, the ends have a cap brazed over after it's filled with magnesium oxide and pounded down.

It is reduced in diameter by being drawn through a circular die, heated to red heat between to anneal. As the outer tube is squeezed, the inner rods are also squeezed. So what started off maybe 3m long, ends up 50 meters long.

The stuff can be run at red heat and not fail. (But not the terminations.) Water MUST be kept out, this is the purpose of the termination. If the unprotected ends get wet,they can be dried out with a blowlamp, starting 300mm from the end and working towards the end.

I think there's also a stainless steel variant these days.

It's very expensive to buy and install. Used in industrial sites/other places where the fire/explosion risk is very high. Finding someone who can do it these days is very unlikely.

That's exactly how it's done. Actually, they only make one size, and it's drawn down to make all the smaller sizes.

For copper, I would guess annealed, and then cold-drawn, but I don't know for sure.

It's magnesium oxide powder, not ceramic.

Yes. Indeed one of the protection features of MICC is that if it's hit with blunt force and compressed, the compressed shape tranfers right through to the conductors and the insulation integrity remains.

The weak point of MICC is that magnesium oxide is hygroscopic, so all cable ends must be gas tight, or the magnesium oxide will absorb moisture and destroy its insulation properties. A well made installation lasts forever, but badly made off cable ends would cause insulation failures after some years.

You see it in lots of commercial premises.

What the hell was it doing under the floorboards of a bungalow?

I expect someone half inched it from their place of work. In days of yore when I was at work, we used only MICC and steel conduit in hospitals. Nobody in their right mind would use it at home if they had to pay for it.

But why half inch that sort of stuff when cable is easier to nick?

In London at one time, the leccy board insisted on it if you wanted to re-site a meter elsewhere in a house - like say when converting into flats.

It could also make sense for a feed outside the house, like say to a garage. Although SWA is more common for this these days.

A question of what won't be missed. Probably chucked in a corner somewhere. Only used infrequently these days. Eg it was used for fire alarm systems at one time, (no longer so) Mostly used in petrol pumps and similar nowadays.

When MICC first came out. it was an alternative to rubber insulated cable.(In steel conduit) But unlike rubber, it didn't deteriorate.

As long as the ends are properly potted to prevent moisture ingress and no tiny movements break the seal.

SteveW

I used MICC in my conservatory. Where much of the wiring had to be surface. Much smaller and neater than any other method. And great fun to work with.

I still see it used in fire protection systems.

Also commonly used in hight combustible buildings (straw bail construction, or close the thatched roofs).

I used it some 45 years ago, to run a supply to my garage.