What will happen if a 120 volt transformer is connected to a 120 volt DC source?

When a 120 volt transformer is connected to a 120 volt DC source, the primary current will indeed cause the transformer to overheat. Transformers are designed to operate with alternating current (AC) because they rely on the changing magnetic field produced by AC to induce voltage in the secondary winding. In contrast, connecting a transformer to a DC source means that the primary winding will draw a constant current, which does not fluctuate.

This constant current can generate excessive heat due to the winding resistance. Without the magnetic field reversing (as it would with AC), the transformer essentially becomes loaded continuously, leading to overheating and potential damage to the transformer. Over time, this overheating may burn out the insulation on the windings and potentially cause failure.

In this case, it is crucial to remember that transformers are not designed to handle direct current, which explains why overheating occurs as a significant risk when connecting to a DC source.