In an SPDT automotive relay, which number signifies the common terminal?

In an SPDT (Single Pole Double Throw) automotive relay, the common terminal is designated by the number 30. This terminal serves as the switch connection that can either connect to terminal 87 (normally open) or terminal 87a (normally closed) depending on the state of the relay.

Understanding the functionality of the common terminal is essential in relay operation. When the relay is energized, the common terminal connects to the normally open terminal 87, allowing current to flow through the connected circuit. Conversely, when the relay is not energized, the common terminal connects to the normally closed terminal 87a, completing the circuit in a different way.

This numbering is standardized in most automotive applications, making it easier for technicians to identify and work with the relay effectively. Having a clear understanding of the terminal designations helps in proper installation and troubleshooting of relay circuits in automotive electronics.