Here is a scenario. You have an older building that has multiple HVAC systems, fans, etc., throughout the building. Each sub system operates independently of one another. One day, the powers that be wants to integrate all these independent systems and control them with a central controller. All these fans and motors are various sizes and voltages running off of separate panels throughout the building.
Question: Does the control signal from the new control panel have to control the existing run circuits at each existing starter or can the existing motor and fan control circuits be looped through the new control panel?
I think the control panel must supply the coil power to the relay coils because by looping the control circuit through the control panel will leave multiple "hot" wires in the control panel even when the control panel is powered off presuming each existing motor starter has its own power source. At the same time a lighting control panel can have multiple circuits feeding the contactor from several panels and have the same issues of multiple "hot" wires in a control panel that is off.
By looping the existing run circuits to the new panel would eliminate the cost of retrofitting all the starters in the building to be compatible to the new control panel but I can not find a reference anywhere this either option is right or wrong.