Resistor spark suppression circuit a

DC relays, contactors and electromagnets are inductive loads. When the coil
is powered off, a high overvoltage will be generated at the contacts due to the existence of self-induced potential . It is added to the contact gap together with the power supply voltage to form spark discharge. This will not only accelerate contact
damage, but also generate a variable frequency signal that seriously interferes with radio communications. Therefore it must be eliminated.
    It must be pointed out that using a spark suppression circuit will delay the operation of relays and other devices.
    The circuit is shown in Figure 6-53. This circuit uses a resistor to provide a discharge circuit for the self-induced potential generated in the coil, so it is called
a resistor spark elimination circuit.
    In the figure, L and R are the inductance and resistance of the coil ,,. is the spark suppression resistor , and S is the moving and closing contact.
    For the circuit in Figure 6-53 (a), 2-3R can be selected; for the circuit in Figure 6-53 (b) , 3-5R can be selected.