...
NC (Normally Closed): A normally closed configuration is used when you want to turn off the relay by default. In this configuration, the relay is always closed and remains closed until you send a signal from the Vutlan monitoring system to the relay module to open the circuit.
NO (Normally Open): A normally open configuration works the other way in which the relay is always open until you send a signal from the Vutlan monitoring system to the relay module to close the circuit.
...