Production of insulated electrical conductors

A method of forming a covering layer of substantially constant diameter upon an electrical conductor, the layer formed from composite material comprising magnetically permeable particles homogeneously mixed with a fluid carrier, the method comprising:

• passing the conductor downwards through a reservoir of the composite material in fluid form and vertically through a die orifice with the composite material applying a pressure at the die orifice to draw the material through the orifice and form the covering layer in fluid form upon the conductor;
• measuring the diameter of the layer as it moves away from the die orifice and sending a signal to an analyzing means which compares the signal with a datum signal corresponding to a desired diameter of the layer;
• and
• upon any difference occurring between the signals, sending a control signal from a control means to operate a valve means which controls the rate of flow of the composite material into or out of a container holding the reservoir of composite material thereby to adjust the height of the reservoir of the material appropriately to adjust the pressure of the composite material at the orifice and change the diameter towards that desired.