A coil powered with DC voltage, an inductive voltage is created anytime power to the coil is de-energized. The inductive voltage is called an inductive kick and it is up to ten times the applied voltage and is in reverse polarity to the applied voltage. A diode or other type of suppression device must be connected across the coil of the solenoid to protect any other electronic components in the circuit that may be damaged by this voltage. The diode is connected in reverse bias across the DC solenoid coil so that when voltage is applied in normal polarity, the diode does not provide a path for current. When the solenoid coil is de-energized, the inductive voltage is the opposite polarity to the power supply, so it will flow through the diode and back into the coil. Since the coil is made of a large length of wire. the energy of the inductive voltage will be dissipated as it moves through the wire. This will render the excessive inductive voltage harmless. slnd-diode-protect_fig4.jpg