Confidential protection circuit for motors

In order to prevent accidental injuries,
when activating the switch buttons of certain equipment, necessary encryption methods are adopted so that non-professionals
cannot rotate the machine tool even if they press the operating buttons, thus protecting equipment and personal safety. The use of this circuit has been proven in practice to be not only very safe, but also very convenient
to use .     The circuit is shown in the figure. During operation, close the knife switch os, first press the SB2 button, and after confirming that it is correct, press the encryption buttons SB3 and SB4 at the same time , so that the circuit controlling the motor can be connected. Only when KM is powered on can the three-phase motor M work. SB1 is a stop button, not an encryption button that the operator does not know (the encryption button can also be installed in a concealed place). In this way, the motor circuit cannot work if a non- operator presses the start button , thus ensuring the safety of electrical equipment.