Normally Open (NO): SPST type - Relays that close and complete the connection when current is sent to them
Normally Closed (NC): SPST type - Relays that open and interrupt the connection when current is sent to them
Change-Over Relays (NO/NC): SPDT type - relays that switch from one circuit to another
Note: The relay case bears an imprint stating "30 amp", this rating is based on a minimum 250,000 cycle life. The manufacturer also certifies a 40 amp capacity based on a minimum 100,000 cycle life.