What is the meaning of Normally Open (NO) and Normally Closed (NC) contacts in relay symbols? NO contacts are open when the relay is off and close when energized, allowing current flow., normally open [NO/H-type] or normally closed [NC/D-type]). A simple 45° slanted line can determine whether a circuit remains open or closed when idle—a small detail with significant implications. Parameter. To effectively resolve red and green light issues on a Vacuum Circuit Breaker (VCB), the essential first step involves discerning the specific engineering meaning of the indicators. The red light invariably signifies the breaker is in an open, tripped, or faulted state, while the green light. Because the E-stop device is operated infrequently, we recommend that you check its function (with the guard closed) regularly, at the start of your shift or daily, to enable the safety monitoring relay to detect single faults. If the guard is rarely opened, the interlock switch must be checked in. Each process condition is called a permissive, and each permissive switch contact is wired in series, so that if any one of them detects an unsafe condition, the circuit will be opened: If all permissive conditions are met, CR 1 will energize and the green lamp will lit. In real life, more than. The International Electrotechnical Commission (IEC) and the American National Standards Institute (ANSI) have established symbol standards that are widely adopted, though some variations exist between regions and industries. A car exercises different types of relays depending on the need of the work, so it is important to know the concept of the normally open and (NC) relay.