Normally Open Relay Vs Normally Closed

Normally closed nc contacts allow current through when the relay or contactor is not energized.

Normally open relay vs normally closed.

When it comes to electrical switches and contacts many people seem to be confused by the terms normally open no and normally closed nc the root of the problem seems to start with the fundamental concept of what it means to be open or closed this post attempts to clarify those concepts. In these systems normally closed relays act as. A normally open is one that is an open circuit until you put voltage and a signal to it. Normally closed relays are used to keep ac unit blowers running even after the air compressor shuts off allowing the system to continue generating residual cool air without running the compressor.

Gas valve control systems. A normally closed relay is one that is a complete circuit and therefore allows voltage to pass through it until it gets a signal and then it opens the circuit. Relays and contactors have two types of contacts each suited for different applications. Normally open no contacts allow current when the relay or contactor is energized.

In other words when voltage is applied to the relay contactor terminals this contact closes. Think of your relay as if it were two ends of as wire.