In electrical systems, NO and NC stand for Normally Open and Normally Closed, respectively. These terms describe the default state of contacts in switches, relays, and contactors when no external force or power is applied. The behavior of NO and NC contacts in relay. An electrical relay consists of a electromagnet and a spring loaded changeover contacts. This is because the current path can either be open or closed. So, these two types work accordingly. The switch may have any number of applications such as contact, break contact, and combination of those two.