History of Mineral Insulated Cables and Copper fire clips and cables

In 1948 Pyrotenax of Hebburn sent us drawings of copper clips, saddles and spacer bars by mistake – the enquiry was meant to go to an Essex Engineering several miles away at Chadwell Heath – but we quoted nonetheless and quoted without charging for tooling. This was a remarkable thing to do since there were 23 different sizes of copper clips, 10 different sizes each of 2 way, 3 way and 4 way copper saddle and half a dozen different spacer bars – and a tool to produce each size would nowadays cost around £6000. By 1956 this was a considerable business producing 800,00 copper clips and saddles regularly each month. Some time in the 70’s Pyrotenax’s Patent expired and BICC (British Insulated Callender Cables) came into manufacturing of Mineral Insulated cable and one year we produced over 20 million copper clips, saddles and spacer bars along with tens of thousands of different terminating tools.

Mineral Insulated cable was made by starting with say a 30ft tube of copper 3” in diameter with ¼ ” wall, putting a pair of ½” diameter conductors inside, to run evenly spaced packed out with mineral, put on a hydraulically  operated drawing bed and literally stretched so that is became say ½” diameter cable with 1/16” conductors running in the mineral. It could be hammered flat, heated to red heat and still conduct the electricity. It became law on all fire alarms and used exclusively in all important installations where fire was a particular hazard and, of course, historic building and churches.

Nowadays, it is made from a continuous coil of copper by gradually forming the flat strip and putting in moulded mineral blocks to space the conductors and seam welding to form the tube. But copper fixing clips and the original terminating tools are still used to hold cable in place and to terminate it to the supply. 

Standards have been modified and nowadays in the UK soft core cable is used where MICC was once the only alternative but still the cable is fixed in place with copper clips and saddles, since copper has a higher melting point than even steel. In places like Dubai, all buildings more than a certain height have to have their electricity supplied by mineral insulated cable because of fire risk and the cables intrinsic physical strength.

News & Articles

Copper has a higher melting point than steel and is the only material used to hold fire alarm cables in place. These cables nowadays can be soft core but for fire alarms Mineral insulated cable is the best available.


Essex Engineering was established in 1935 and moved to its present premises in 1940. During the 2nd World War, it made metal stampings for the MOD. After the war, in 1948 it started to produce the range of copper clips and saddles for Pyrotenax cable (mineral insulated cable) together with the terminating tools necessary for installation.


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