As I understand it, an EDACS TRS, is not limited in what channels it can assign as a control channel. However, the controller does like to keep a standard rotation with two or more channels on a daily basis. If for any reason the transmitters on all the regular control channels should fail, the controller can then select a normal voice channel as an alternative control channel, until the system is repaired.
I know Jackson County has been watching the developments in Ingham County, and it will be interesting to see what direction they will pursue in regards to their future communications system.
73's
Ron