Wetting current

In electrical engineering, wetting current (sometimes also spelled as whetting current in archaic sources) is the minimum electric current needing to flow through a contact to break through the surface film resistance at a contact. It is typically far below the contact's nominal maximum current rating.In some low voltage applications where switching current is below the manufacturer's wetting current specification, a capacitor discharge method may be employed by placing a small snubber capacitor across the switch contacts to boost the current through contact surface upon contact closure.A related term sealing current (aka wetting current or fritt current) is widely used in the telecommunication industry describing a small constant DC current (typically 1-20 mA) in copper wire loops in order to avoid contact oxidation of contacts and splices. It is defined in ITU-T G.992.3 for 'all digital mode ADSL' as a current flowing from the ATU-C (ADSL Linecard) via the phone lines to the ATU-R (CPE).Contact cleaner can be applied to the contact surfaces to inhibit the formation of resistive surface films and/or to ameliorate existing films.