Protective equipment for protecting against voltage surges, the protective equipment comprising a modular block that is provided with a housing for receiving at least one lightning arrester cartridge, the protective equipment being characterized in that said modular block houses a shaft referred to as a "cartridge locking shaft" that is provided with at least one locking element (191; 191'), wherein • the shaft is mounted to move in the modular block in such a manner that its movement is associated with the movement of the opening-and-closing device of the circuit breaker; • said cartridge locking shaft is capable of taking up two distinct positions, namely firstly a first position, referred to as a "safe position", that corresponds to the non-tripped state of the circuit breaker, in which safe position each locking element co-operates with a complementary portion of a lightning arrester cartridge so as to prevent said lightning arrester cartridge from being removed and/or inserted, and secondly a second position, referred to as an "access position", that corresponds to the tripped state of the circuit breaker, in which access position each locking element leaves said complementary portion of the lightning arrester cartridge free so as to allow said lightning arrester cartridge to be removed and/or inserted; and • the cartridge locking shaft carries at least one lug forming a locking element, and it is pivotally mounted in the modular block so that one of its ends is to be constrained in pivoting with the opening-and-closing device of the circuit breaker, so as to take up two distinct angular positions, namely the safe position in which each lug projects into the housing of the modular block, and the access position in which each lug is situated set back from said housing of the modular block. • the shaft is mounted to move in the modular block in such a manner that its movement is associated with the movement of the opening-and-closing device of the circuit breaker; • said cartridge locking shaft is capable of taking up two distinct positions, namely firstly a first position, referred to as a "safe position", that corresponds to the non-tripped state of the circuit breaker, in which safe position each locking element co-operates with a complementary portion of a lightning arrester cartridge so as to prevent said lightning arrester cartridge from being removed and/or inserted, and secondly a second position, referred to as an "access position", that corresponds to the tripped state of the circuit breaker, in which access position each locking element leaves said complementary portion of the lightning arrester cartridge free so as to allow said lightning arrester cartridge to be removed and/or inserted; and • the cartridge locking shaft carries at least one lug forming a locking element, and it is pivotally mounted in the modular block so that one of its ends is to be constrained in pivoting with the opening-and-closing device of the circuit breaker, so as to take up two distinct angular positions, namely the safe position in which each lug projects into the housing of the modular block, and the access position in which each lug is situated set back from said housing of the modular block.