LearnTronics
One Relay, Several Contacts
One coil can operate many contacts
A relay can have one normally open contact, one normally closed contact, several of each, or changeover contacts that provide both paths.
NO and NC describe the de-energized state
| K1 coil | K1 NO contact | K1 NC contact |
|---|---|---|
| 0 / de-energized | open | closed |
| 1 / energized | closed | open |
When the coil energizes, the armature moves and all contacts operated by that armature change state.
Ganged does not mean electrically connected
Several contacts may be mechanically ganged because the same relay armature operates them. That does not mean those contacts share the same electrical circuit.
One contact might switch a 24-volt control signal while another switches a completely separate indication circuit.
Relay contact descriptions
Terms such as SPST, SPDT, DPDT, and similar abbreviations describe the number of poles and throws. We will use them later, but the first skill is simply recognizing which contacts are normally open and normally closed and which coil operates them.