Abstract: The exclusion circuit includes a normally de-energized relay and a normally non-conducting Darlington pair circuit powered from the key telephone system power supply. The Darlington pair circuit is maintained non-conducting and the relay is maintained de-energized when one of the telephones of a non-excluded group of telephones goes off-hook before one of the telephones of the excluded group of telephones goes off-hook to prevent the one of the telephones of the excluded group of telephones from having access to the excluded central office line, while the Darlington pair circuit is rendered conductive for actuating the relay when one of the telephones of the excluded group of telephones goes off-hook before the one of the telephones of the non-excluded group of telephones goes off-hook to allow the one of the telephones of the excluded group of telephones to have access to the excluded central office line.