Solution

To solve this, let us first understand the normal operation (motor spinning)

· The motor has coils that rotate inside a magnetic field.
· According to Faraday's Law, as the coil rotates in the magnetic field, a voltage is induced in the opposite direction to the current feeding it. This voltage is called back electromotive force (back EMF, or CEMF).
· The back EMF acts as a "natural regulator": it opposes the source voltage and limits the current flowing through the coils.
· The resulting current is small (only what is needed to overcome the mechanical load and losses), and the motor runs stably without overheating.

Now let us analyze the case of a locked rotor (motor stalled)

If the rotor stops due to an overload or jam:

· There is no motion → no magnetic flux change → the back EMF disappears.
· With the opposition gone, the source voltage (V) is applied directly across the ohmic resistance (R) of the coils, which is very small.
· By Ohm's Law, the current surges to a very high value:
I_{\text{start}} = \frac{V}{R}
· This current is 5 to 10 times higher than the rated current. All this electrical energy is converted into heat (Joule effect: P = I^2 R).

As a result:
The extreme heat melts the insulating enamel on the wires, causes internal short circuits, and burns out the motor.