These device is consist of a coil of wire is covered with an iron core. When electricity is applied to an v1 & v2 means coil of wire it becomes magnetic, hence the term electro magnet. The A,B & C terminals are SPDT Switch controlled by an electro magnet. When electricity is applied to v1 & v2, the electromagnet acts upon the SPDT switch so that the B, C terminals are connected. When the electricity is disconnected, then A,C terminals are connected. If electricity is disconnected, some current present in that coil. During turn off the reverse emf don’t worked means, we are using flywheel diode. These diode don’t allow the current in the previous block.