What occurs when the secondary side of a transformer is connected first?

Connecting the secondary side of a transformer first is generally accepted practice due to the operational characteristics of transformers. When the secondary side is energized first, it allows for the load to be connected securely before energizing the primary side. This is crucial because it helps prevent damage to the transformer and any sensitive equipment connected to the secondary side.

In practical scenarios, connecting the secondary first ensures that any fault conditions, such as short circuits, will only involve the secondary circuit. Energizing the primary with an already connected load might lead to incorrect voltage levels or surges, which could cause stress on the transformer or connected equipment.

This method is often implemented to manage safety and operational reliability, ensuring all systems are ready before applying line voltage. Hence, it is considered an acceptable and secure practice within standard operating procedures for working with transformers.