Abstract: The series connection of a normal close contact to the mam contactor coil of a JJ1 series auto pressure reducing starting cabinet can achieve noise silencing and energy saving. But it is difficult with the LB(N)Z series operating stack to control the shutdown button with two normal close contacts in explosion and water hazard place. Through the study on block driagram of starting cabinet, it is concluded that it is feasible to remove the other normal contact for perfecting equipment performance. The reason is that the releasing time of main contactor coil when pushing the shutdown button is shorter than the time delay of the operator's consciousness, and therefore, the system can operate normally.