This standard applies to the protection system of a nuclear reactor and, more especially, to all interconnections between a reactor protection system and all other systems and equipment not part of the protection system, except: the physical connection between sensors of the protection system and the physical variables that they monitor, the electrical connection between the protection system and the reactor control rods or other safety mechanism, and the electrical and pneumatic connections to the power distribution system (mains) and pneumatic supplies that supply power to the protection system. It applies mainly to protection systems in nuclear power reactors. Its object is to supplement and interpret the requirements of sub-clause 5.5.1 of IEC Publication 231 A. This standard provides assistance in the implementation of this sub-clause.