Magnetic flux leakage is a significant item in dispersed losses and in caged rotors, most rotors occur leakage currents from the bars to the core slides as they look for the shortest path through the iron of a short circuit ring to the other.

For nearly half a century, various methods have already been suggested to block these leakage currents through an insulation between the bars and the magnetic core. Chemical and metallurgical processes have been tested in order to isolate the bars from the cage or the surface of the core blades where they form the grooves of the bars.

Most of the methods were inefficient or very costly and one reason for this is that the treatment of the core in a caged rotor needs to withstand the injection temperatures of the aluminum. Another problem is the inevitable swelling and contraction that materials suffer in an uneven manner as the machine heats up when it comes into service and cools off. retractable hose reels

An alternative way of dealing with the problem was to use conductive covers in order to reduce the core-to-core resistance, and found even greater failure rate for small and medium-sized engines produced on a large scale.