What does it mean if a train operator has slippered a contact shoe?

When a train operator has slippered a contact shoe, it refers to the action of placing a shoe paddle between the third rail and the contact shoe. This is an important step for ensuring the train receives adequate electrical power for operations. The contact shoe is responsible for making contact with the third rail, which supplies electricity to the train. By inserting a shoe paddle, the train operator is effectively enhancing the connection and facilitating the flow of electricity, which is critical for system functionality.

In this context, the other options do not accurately reflect the specific action of slippering a contact shoe, as they pertain to different operational procedures or adjustments unrelated to the direct electrical connection between the third rail and the train.