This paper is concerned with the investigation of the motion of an air arc plasma in a quenching chamber, in particular with the effect of different chamber widths and outlet areas. A simplified arc chamber of a low-voltage switch device is used for the analysis. Based on a set of governing equations, a 3-D air arc plasma model is constructed and solved by a commercial code. It is found that increasing both the chamber width and the outlet area leads to an increase in the arc speed, but the strength of the dependence varies, depending on the values of the chamber width and the outlet areas. The tail of the arc column becomes shorter as the chamber width is reduced. This is shown due to the reduction in the backward flow by the squeezing of the two flow vortices that occurs.