Current production plants are highly customizable and flexible in their processes. This flexibility is mainly realized by software. Standards like IEC 61508 for functional safety demand intensive testing efforts to ensure a certain level of integrity. The uncertainty about system behavior, especially in fault situations, complicates reliability testing. We propose a concept that integrates fault models into SysML system models for model based development. The introduced fault models can be designed in two granularity levels, starting with coarse information at early development phases up to precise mathematical relations. The concept is applied to a component (rotary switch) of a laboratory plant, which connects three conveyor bands where friction deviation can occur during rotary movement. Such models can build the foundation for test generation in reliability testing.