Contact protection

Conversely, they “turn power off” when the moving electrode breaks contact and the resulting arc plasma stops burning as the dielectric gap widens sufficiently to prevent current flow.

These different ratings are due to contacts being designed to compensate for the destructive arcing that naturally occurs between the electrodes during normal Wet operation.

[1] When the contact is operating under power (wet), the sources of the wear are the result of high current densities in microscopic areas, and the electric arc.

Heating due to arcing and high current density can melt the contact surface temporarily.

Below 2 Amperes, a variety of transient suppressing electronic components have been employed with varying success as arc suppressors, including: capacitors, snubbers, diodes, Zener diodes, transient voltage suppressors (TVS), resistors, varistors or in-rush current limiters (PTC and NTC resistors).

[9] However, this is the least effective method as these neither significantly influence the creation of nor suppress the arc between the contacts of electromechanical power switches, relays and contactors.

Typical contact elements of an electromechanical relay or contactor.
From left to right:
  1. Pristine contacts from a relay
  2. The nearly destroyed contacts from a relay operated under power for nearly 100,000 cycles
Contact Protection Using Electronic Power Contact Arc Suppression - from left to right: new contact (out of box); failed contact with < 100K unprotected cycles; "like new" contact after 100K protected cycles; and "like new" contact after 1 million protected cycles.