Is the NC contact of a relay normally open or normally closed?
2 Answers
Relay NC is a normally closed contact, which refers to a contact that remains closed and conductive when no power is applied. A contact refers to the output form where the load current is not connected when the detection body is inactive. The working principle of a relay is: when the change in the input quantity meets specified requirements, it causes a predetermined step change in the controlled quantity within the electrical output circuit. Relays are used in automated control circuits as automatic switches that use small currents to control the operation of large currents. Their functions in circuits include: 1. Automatic regulation; 2. Safety protection; 3. Circuit switching. They are categorized into normally open type, normally closed type, and changeover type.
Once my car suddenly wouldn't start, the mechanic pointed to the relay in the fuse box and told me that the one labeled NC stands for Normally Closed contacts. Normally Closed means that when the relay is not energized, those two terminals are originally in a connected state, just like the default closed position of a household switch. If the relay fails and causes the NC contacts to not close, it's equivalent to the entire circuit being open, causing components like headlights and air conditioning to stop working directly. The problem was solved after replacing the relay. During inspection, using a multimeter to test continuity was particularly accurate. Remembering the Normally Closed characteristic of NC is very useful for troubleshooting circuit faults.
