Question 445Electricity & Electronics - QMED

The correct answer is A) welded contacts. If a magnetic controller relay fails to drop out when the coil voltage is removed, the most probable cause is that the contacts have become welded or stuck together. This can happen due to excessive current or arcing across the contacts, which can cause the metal surfaces to fuse together. When the contacts are welded, they will not open even when the coil voltage is removed, preventing the relay from dropping out as it should. The other options are less likely causes. Excessive current (B) can contribute to welded contacts, but is not the primary reason for the relay failure. Excessive spring tension (C) or overvoltage (D) are not the main factors in this scenario where the relay fails to drop out.