This master thesis’s subject is to model an ABB contactor’s dynamics and to develop a hardware-in-the-loop simulation environment. The hardware-in-the-loop method utilizes computer models that are simulated in a real-time simulator. The real-time simulator is connected to hardware components. A contactor is an electrically controlled mechanical switching device and it is used in circuits where large currents can occur. In this thesis, the contactor is divided into three separate subsystems and models are developed for each of them. The three subsystems correspond to the contactor’s mechanics, electromagnetics and electronic components. Computer models are implemented in MATLAB and Simulink to realize the subsystems. The hardware part, of the hardware-in-the-loop simulations, consists of electronic parts that are not modeled. To connect the hardware part to a real-time simulator, from dSPACE, a hardware interface was constructed. This report focuses on the modeling of the mechanics and the electromagnetics as well as the software implementations. The thesis work was carried out in collaboration with another student. The focuses of his report are the modeling of the electronics and the construction of the hardware interface. Validation of the hardware-in-the-loop simulations is done by using measurements collected from a real contactor. The conclusion is that the simulations of the contactor’s behavior correspond well with a real contactor.