The slot motor is used in high-power devices to open a circuit when the current exceeds a limiting value. It is critical for the proper functioning of the device, to predict exactly the force produced by the current. In this paper, the three-dimensional magnetostatic field within the motor is analyzed by solving directly for magnetic flux density and the results are used to predict the forces generated. The results are then verified experimentally. This paper also introduces the concept of the fictitious vector potential for the graphical display of three-dimensional magnetic fields.