Arc suppression is the reduction of the electric arc energy that occurs when current-carrying contacts are opened and closed. An electric arc is a man-made, continuous arc-discharge consisting of highly energized electrons and ions supported by an electric current of at least 100mA; not to be confused with an electric spark.

Every time an electrical power device (for example: heaters, lamps, motors, transformers or similar power loads) turns on or off, its switch, relay or contactor transitions either from a CLOSED to an OPEN state ("BREAK") or from an OPEN to a CLOSED state ("MAKE"), under load, an electrical arc occurs between the two contact points (electrodes) of the switch.

The temperature of the resulting electric arc is very high (tens of thousands of degrees), causing the metal on the contact surfaces to melt, pool and migrate with the current. The high temperature of the arc causes dissociation of the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter. This very activity causes the material in the contacts to degrade quickly, resulting in device failure.

Understanding arc suppression requires an understanding of both arcing and arc initiation mechanisms. Contact arcs are either a Thermionic-Emission-Initiated-Arc ("T-Arc") or a Field-Emissions-Initiated-Arc ("F-Arc"), and are maintained by a continuous supply of power (think of an arc welder or a Xenon arc lamp).:

While arcing occurs during both the BREAK and MAKE transitions, the break arc is typically more energetic and thus more destructive.

During contact MAKE, F-Arc initiation occurs as the moving electrode nears the stationary electrode. Then the MAKE F-Arc plasma ignites and is promptly extinguished at the instant of contact impact. This initial impact results in a series of plasma pressure amplified MAKE bounces, with each bounce yielding a T-Arc. These bounces continue until the contact is micro-welded in the CLOSED position. (Note that "arc suppression" does not mean "arc elimination", as some tiny arcs ("arclets") yield beneficial micro-welds. These micro-welds are a desired and important power contact feature as they ensure vibration-resistant, low ohmic, and non-permanent electrode connections.)

The "BREAK Arc" consists of an initial BREAK T-Arc that may be extended by a series of BREAK F-arcs. The initial BREAK T-Arc is created after the explosion of the super-heated molten-metal bridge that had been carrying current as the contact begins to open. As the BREAK T-Arc plasma extinguishes and current is interrupted, inductance in the loop extends the duration of the "BREAK Arc" by initiating a series of BREAK F-Arcs which continue until the contact gap widens beyond the thermodynamic ability to support the burning plasma.

There are several possible areas of use of arc suppression methods, among them metal film deposition and sputtering, electrostatic processes where electrical arcs are not desired (such as powder painting, air purification, and contact current arc suppression. In industrial, military and consumer electronic design, the latter method generally applies to devices such as electromechanical power switches, relays and contactors. In this context, arc suppression is contact protection.