I am wanting to connect a volt free contact to my Hikvision NVR so that when the alarm is set I can trigger the input on the NVR to start alerts etc. 

 

I just cannot workout what OP3 is, if volt free I would have expected to see a ground terminal so I can connect to OP3 and ground and then this would act as a switch for the NVR. 

Volt free would be a relay so would be marked COM/NC/NO, if it's a single terminal it will be switched output so you will need a relay.

Manual will say if it's +ve/-ve applied or removed then you need to use an auxiliary voltage for the other coil side of the relay.

 

Should be transistorised relay too due to possible back EMF.

or just connect a relay to the output and voila! 

As above, I would use a 12v dc relay personally and power it from a little 12v independent psu (as it’s an NVR you probably won’t have a 12vdc PSU powering any cameras as everything will likely be Poe) 

Wouldn't expect the NVR needs 12V just a closed loop on it's own input/output, hence needing a relay.

Voltages shouldn't be shared between them

Agreed

12 hours ago, aissecur said:

As above, I would use a 12v dc relay personally and power it from a little 12v independent psu (as it’s an NVR you probably won’t have a 12vdc PSU powering any cameras as everything will likely be Poe) 

He is after a voltage free output, and the panel will drive the relay, adding another PSU will only complicate things