This European Standard specifies, as for Home or Building Electronic Systems (HBES) for the domain of Building Automation and Control System Application and Building Management (BACS), common rules for a class of multi-application bus systems where the functions are decentralised and linked through a common communication process. This European Standard sets the basic requirements for products and systems. The requirements may also apply to the distributed functions of any equipment connected in a home or building control system if no specific standard exists for this equipment or system. Due to its reference to the EN 50090 series, this European Standard sets requirements for the BACS area in relation to Architecture and Hardware and Application and Communication of systems based on HBES amongst other areas, and specifies the basic requirements for interoperability (between products and systems). Aspects such as environmental conditions/external influences, electrical safety, EMC, etc. also used to be covered by EN 50090-2-2, which will be superseded by the now available EN 50491 series. The latter European Standards series was jointly developed by CENELEC/TC 205 and CEN/TC 247 and will in the future also include aspects like functional safety in normal use (now contained in the EN 50090-2-3). The EN 50491 series applies, together with the relevant product standard for devices, if applicable.