I have a situation that I have never run into: the customer is asking for multiple ways to control the lights in a large complex. This is what they want.
first the simple part: 1 photocell that will turn on all the contactors at one time.
second: be able to turn on any one contactor without turning on the others (this is for maintenance of individual areas during the day). I figured simple enough, use a 3-way or 3-position switch on all the contactors so I can have them all on photocell and can switch to manual control with any switch to the contactor of choice.
now they want the big part: also be able to turn on any individual contactor with a remote computer or phone. They have the relays to do it.
But the question is how to keep them all separate. If I tie the relay to the photocell side, then they all will come on. If I tie to the manual side then they would need to flip the switch to manual, meaning the remote from the phone would be useless.
Because they want phone or internet control of this system (and that is a reasonable request these days), you are absolutely married to a home-automation scheme like Wemo or HomeKit.
That means you have two choices: you can build the other controls so they are locked in mortal combat with the automation... Or you can integrate the other controls into the automation using recommended methods. Given that it's for a customer, you're pretty much forced into the second choice. If you are not willing to "skill up" in this area, get a subcontractor.
A plc with multiple zones is a normal part of most industrial sites, overides for zones and photocell , very simple program, photocell turns on all outputs that energise contactors , separate switches 1 input for each contactor provides manual overide control. For a DIY project this could be done with an arduino or similar micro controller.