What is the primary characteristic of a normally open relay?

A normally open relay is primarily characterized by its contacts, which remain open (not allowing current flow) until the relay is energized, at which point the contacts close and allow current to flow through the circuit.

The reason option B is correct is that the relay contacts are indeed held open by a spring mechanism. This spring action ensures that the contacts do not make contact under normal conditions, meaning that the circuit remains open and inactive until an electrical signal energizes the coil of the relay. When the coil is energized, it creates a magnetic field that overcomes the spring tension, pulling the contacts closed and allowing current to flow.

Understanding the operation of a normally open relay is crucial in various electronic systems, as it serves as a control mechanism to manage the flow of electricity in a circuit. This functionality is widely used in automation, where devices need to be turned on or off in response to various triggers.

While the other options reference different characteristics of relay operation, they do not accurately describe the nature of a normally open relay. For instance, permanently closed contacts refer to normally closed relays, while manually controlled contacts imply a different operational mode not characteristic of an open relay.