Why is there a spark in the relay contacts? Suppose that the coil and the contacts are connected to two different power supplies. If i suddenly disconnect the power supply to the coil, then the voltage across the coil will increase and a spark will jump across the switch that I used to disconnect the power supply from the coil. But the relay contacts are isolated from the coil circuit, and should be unaffected by the voltage from the coil. The only way for a spark to jump across the contacts is if there is an inductive load connected to it. I am asking this, because every time I read about this topic online, they say that it is due to the voltage in the relay coil. Thank you for your time.