Which of the following is a common reason for transformer failures?

C is identified as a common reason for transformer failures because transformers are highly sensitive to their operating environment and load conditions. Overloads occur when a transformer is subjected to a higher current draw than it is rated for, leading to overheating, insulation breakdown, or even catastrophic failure. Shorted loads can cause excessive current flow, which similarly stresses the transformer's components and can result in failure.

Additionally, environmental factors like extreme temperatures, humidity, and the presence of contaminants can adversely affect a transformer's performance and longevity. Proper maintenance and monitoring of these conditions are critical in preventing failures.

On the other hand, while excessive power loss, faulty capacitors, and inadequate grounding can lead to issues in electrical systems, they are not as directly related to transformer failures as the combined stress of environmental factors and load conditions.