Question 179Electricity & Electronics - 1st Asst/Chief

The correct answer is C) low voltage on the operating coil. When the operating coil of a magnetic relay experiences low voltage, it can cause the contacts to chatter or buzz loudly, leading to welding of the contacts. This is because the low voltage is insufficient to fully energize the coil and pull the contacts together firmly, leading to an unstable connection and the buzzing/welding effect. The other options are incorrect because: A) lubrication of the contacts would not cause buzzing or welding, B) overheating of the coil would more likely lead to the relay failing to operate, and D) low insulation resistance to ground would not specifically result in the described symptoms.