Is there an electrical connection between upper and lower cage in double cage induction motors?

There are two types of induction motors which have double rotor slots. In the first type, both slots,upper and inner, are filled with the same conducting material (aluminum for example) and as a consequence the motor has a single cage finaly, despite the double rotor slots. In the second type, usually different materials are to fill the upper and inner rotor slots (for example aluminum for the upper slots and copper for the inner slots). So, in this category the motor has two electrically independant rotor cages.

Hi Dear Monjezi
There are two type end-rings, Separated and Connected end-rings in double cage motors.

Hi Shadman,
Both windings are independent electrically. The outer cage consists of bars of high resistance metal, whereas the inner cage has low-resistance copper bars. Thus the outer cage has a high resistance with low reactance to resistance ratio and the inner cage has low resistance but high reactance to resistance ratio. but as the power dissipated during operation is divided among them they are considered parallel when equivalent circuit is drawn.

The only way for the two windings of any type (coils OR bars) to be electrically independent is: 1) insulate each winding with some form of groundwall, and 2) leave the ends of of the windings unconnected from each other.

In the case of most double-cage windings, there is some form of electrical pathway between the upper cage material (which is in direct contact with the lamination steel) and the lower cage (which is ALSO in direct contact with the lamination steel).

Usually, the choice for a double-cage arrangement boils down to optimization of the overall cage performance between two "standard" materials available to a manufacturer: one is often a high resistance material and the other is a low resistance material. When combined, the result is a somewhat-balanced "medium" resistance material.