SIL classification for intelligent motor control systems in accordance with the ATEX directive

While the motor management system and its hardware control devices is part of a low voltage assembly the Low Voltage directive applies. This directive refers to European standards that have their own requirements. But how to interpret other EU directives to classify and certify motor management systems including motor protection as part of low voltage switchgear? This paper describes the "route of the process" based on experience obtained during the certification process of an electronic motor protection device as part of motor management system and its failsafe hardware control devices in a low voltage assembly and the effort of how to find the correct product and safety standards that apply for a complete system. The requirements of the ATEX directive 94/9/EC Annex II (Essential Health and Safety Requirements) are covered by compliance with the European Safety standards, in which SIL is used as a method to define the (for the process) required safety level of a system consisting of safety related devices for equipment used in various zones within potentially explosive areas. Because there are no specific product standards available and they operate in a wide area where various directives are applicable, it is a challenge to find the right European standards to meet the relevant demands. Process industries require a safety integrity level (SIL) classification for a larger chain of control and protection equipment, from which the product certification in terms of MTBF, safe failure fraction (SFF) and diagnostic coverage (DC) is a part of, in order to rate the safety level in hazardous areas.