This standard is applicable to nuclear power plant instrumentation and control (I&C) systems, and their cables, that are important to safety, as defined in IAEA Safety Guide NS-G-1.3. It is also applicable to temporary installations which are part of those I&C systems important to safety (for example, auxiliary equipment for commissioning tests and experiments). Clause 6 is intended particularly for the cabling of the I&C systems important to safety. This standard applies to the I&C of new nuclear power plants as well as to I&C upgrading or back-fitting of existing plants. For existing plants, only a subset of the requirements is applicable; this subset is to be identified at the beginning of any project. Where independence is required by general safety standards such as IAEA safety guides or IEC 61513, one aspect of achieving this independence is physical separation between the systems and their equipment that perform functions important to safety. This standard defines the assessments needed and the technical requirements to be met for I&C systems important to safety and their cables, in order to achieve adequate physical separation between redundant sections of a system and between a system and another system. This separation is needed to prevent or minimise the impact on safety that could result from faults and failures which could be propagated or affect several sections of a system or several systems.