Contact Form

Basics

Contact Form

1. SPST-NO (Single Pole Single Throw Normally Open)

The contacts close when the switch is operated. They are normally open.

  • SPST-NO OFFThe contacts are separated while the switch is not pressed, so the circuit is not connected and the lamp is not lit.
  • SPST-NO ONWhen the switch is pressed, the contacts come into contact, closing the circuit and lighting the lamp.

Use NO contacts when you want the load to operate when the switch is operated.

2. SPST-NC (Single Pole Single Throw Normally Closed)

The contacts open when the switch is operated. They are normally closed.

SPST-NC

  • While the switch is not pressed, the circuit is connected and the lamp is lit.
    When the switch is pressed, the contacts separate, opening the circuit and causing the lamp to go out.

Use NC contacts when you want the load to stop operating when the switch is operated.

3. SPDT (Single Pole Double Throw)

Changeover contacts have the functions of the both NO and NC contacts.

SPDT

Use changeover contacts when you want to switch two circuits when the switch is operated.