An interlock arrangement between a pair of industrial rated circuit breakers in adjoining circuit breaker compartments utilizes a pair of circuit breaker interlock units, one mounted on the rear surface of each circuit breaker. A corresponding pair of compartment interlock units are arranged within the circuit breaker compartments for interaction between the two circuit breaker interlock units to open the contacts within one of the circuit breakers when an attempt is made to electrically connect the circuit breaker within one compartment when the circuit breaker in the adjoining compartment is already electrically connected within the adjoining compartment.