In an electrical circuit, what causes arcing across the contacts of a panel board switch when it is opened?

Arcing across the contacts of a panel board switch when it is opened is primarily caused by the magnetic energy induced by inductance in the circuit. When the circuit is broken, the inductive load can generate a high voltage spike due to the collapse of the magnetic field. This sudden change can cause a momentary discharge of electricity, resulting in arcing.

Inductance in a circuit creates a magnetic field when current flows. When the circuit is interrupted, the energy stored in that magnetic field may seek a path to continue flowing, often causing a spark or arc as the contacts of the switch separate. This arcing can damage the contacts over time and can lead to further operational issues within the electrical system.

Other factors such as current flow, short circuits, or circuit overloading can contribute to electrical issues, but the specific phenomenon of arcing during the opening of a switch is closely related to the presence of inductance and the resultant magnetic energy that is released.