What is the minimum requirement for a START-STOP momentary-contact pushbutton station?

• A. One set of contacts
• B. Two sets of contacts - one normally open and one normally closed
• C. Three sets of contacts
• D. Four sets of contacts

Answer: (B)

The minimum requirement for a START-STOP momentary-contact pushbutton station is two sets of contacts: one normally open (NO) and one normally closed (NC).

The normally open contact is typically used for the START function. When the button is pressed, this contact closes and completes the circuit, allowing current to flow and start the motor or device. Conversely, the normally closed contact is used for the STOP function. When the button is pressed, this contact opens, interrupting the circuit and stopping the operation of the device.

Having both types of contacts allows for effective control of the equipment, ensuring that it can be easily started and stopped using a single pushbutton with distinct and reliable actions. This design is essential for safety and operational efficiency in control circuits.

In contrast, a single set of contacts would not offer both START and STOP functionalities, while three or four sets of contacts would be more than necessary for a simple start-stop application.