electrical and electronics engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

, wetting current is the minimum

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

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. A thin film of oxidation, or an otherwise passivated layer, tends to form in most environments, particularly those with high

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

, and, along with surface roughness, contributes to the

contact resistance Electrical contact resistance (ECR, or simply contact resistance) is resistance to the flow of electric current caused by incomplete contact of the surfaces through which the current is flowing, and by films or oxide layers on the contacting sur ...

at an interface. Providing a sufficient amount of wetting current is a crucial step in designing circuits that use

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...

es with low contact pressure. Failing to do this might result in switches remaining electrically "open" when pressed, due to contact oxidation.

Capacitor discharge solution

In some low voltage applications, where switching current is below the manufacturer's wetting current specification, a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

discharge method may be employed by placing a small capacitor across the switch contacts to boost the current through contact surface upon contact closure.

Sealing current

A related term sealing current (aka wetting current or fritting 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 The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...

G.992.3 for "all digital mode ADSL" as a current flowing from the ATU-C (

ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over Copper wire, copper telephone lines than a conventional voiceband modem ...

Linecard) via the phone lines to the

ATU-R A digital subscriber line (DSL) modem is a device used to connect a computer or Router (computing), router to a telephone line which provides the digital subscriber line (DSL) service for connection to the Internet, which is often called ''DSL ...

( CPE). Carbon brushes develop high resistance glaze when they're used without current flow for an extended period. A special circuit is utilized for turbines and generators to introduce current through the brushes into the shaft to prevent this contact fritting.

Contact cleaner

Contact cleaner can be applied to the contact surfaces to inhibit the formation of resistive surface films and/or to ameliorate existing films.

Capacitor discharge solution

Sealing current

Contact cleaner

See also

References

Further reading