Hello,

I have a simple question. I'm trying to wire up this phone intercom system to be able to trigger our electronic door locks. Everything so far is working fine - i'm just not sure i'm understanding the wiring correctly for the relay to trigger the door lock:

We have a door with key-card access so when you use your keycard, the brain sends a switched 12v signal to the electronic solenoid to open the door. I'm adding in this other relay which we can trigger with our phones - i need to be able to provide 12v to the solenoid to open the door. From the attached diagram am I doing this right?

 

Connect the black wires (0V) together, the 12V supply to NO of the relay and the 12V of the solenoid to NC of the relay.

 

I believe you should add 2 diodes to protect both power sources from seeing each other. So it won't matter when one is on and the other is off, or if both are on at the same instant. The small voltage drop caused by the diode shouldn't make any difference to the solenoid, but you'll need to be sure your diodes can handle the solenoid current. Nevermind if the source in both cases is the same 12v power supply.