When are Form B contacts open?

Form B contacts are designed to operate in a specific manner concerning the presence or absence of an energizing force. They are normally closed when the energizing force is applied, meaning they allow current to flow through them in that state. It is only when the energizing force is removed that the Form B contacts open, interrupting the circuit.

This characteristic is crucial in safety and control systems because Form B contacts can act as a fail-safe by removing power or stopping a circuit when conditions change, such as a loss of power or a need to interrupt operations for maintenance. Understanding the operation of Form B contacts helps ensure appropriate design and application in relay logic and control systems, which is essential knowledge for someone preparing for the NETA ETT Certification.