Main Articel: [[Definition of Terms and Symbols| Definition of Terms and Symbols]]
*'''Electrical contact''' is a property which is generated through the touching of
two electrically conducting surfaces.
*'''Contact part''' is a metallic component which is designed to create or interrupt
an electrical contact (is frequently replaced by the term “contact” if it is clearly
understandable that a physical piece or item is meant).
*'''Contact area''' is the whole area on a contact part that may be used for
contacting.
*'''Apparent contact area A<sub>s</sub>''' is the part of the contact area on contact parts that
can make physical contact during the touching of two contacts.
*'''Load bearing contact area A<sub>t</sub>''' is the part of the apparent contact area which
is affected by the contact force. It is the sum of all microscopic actual touching
points.
*'''Effective contact area A<sub>w</sub>''' is the part of the load bearing contact area through
which current is flowing and therefore the sum of all current carrying touching
areas (a-spots), A<sub>w</sub>< A<sub>t</sub>< A<sub>s</sub>.
*'''Contour area A<sub>n</sub>''' is the contiguous area which includes all effective
a-spots, A<sub>w</sub>< A<sub>n</sub>< A<sub>s</sub>; A<sub>n</sub>≠ A<sub>t</sub>.
*'''Contact resistance R<sub>k</sub>''' is composed of the constriction resistance and the film
resistance.
*'''Constriction resistance R<sub>e</sub>''' is the incremental electrical resistance generated
by the constriction of the currents paths in the touching area
(a-spot).
*'''Film resistance R<sub>f</sub>''' is generated by a foreign matter layer, which for ex. is
formed by a reaction of the contact material surface with the surrounding
atmosphere (a surface film is a substance on the contact surface with
different properties than those of the actual contact material).
*'''Path resistance R<sub>d</sub>''' is the total electrical resistance between reference
points (usually the device terminals) which can be freely chosen but must
be defined. It is the sum of the conductor resistance R<sub>b</sub> and the contact resistance R<sub>k</sub>.
*'''Contact force F<sub>k</sub>''' is the force that is exerted between the two contact
parts in the closed position.
*'''Frictional wear''' is the loss of material caused by mechanical wear
between contact parts.
*'''Bounce''' is the single or multiple interruption of conduction between
contact parts during the make operation caused by alternating
transformation of kinetic to potential energy.
*'''Contact wear''' includes all changes on a contact surface. Mechanical
and electrical wear must be distinguished.
*'''Material transfer''' is the transfer of contact material from one contact
part to the other. It occurs mainly during switching of DC loads. The
direction of the transfer depends on the load circuit properties and the
contact materials used.
*'''Arc erosion''' is the loss of material into the surrounding of the contact
spot which is generated by electrical arcing. It occurs during contact make
as well as break operations.
*'''Contact welding''' occurs when melt-liquefied touching areas of the
contact parts come in contact with each other. The melting occurs during
high current carrying through these areas. During make operations this
occurs through bounce arcs, on closed contacts a too high contact
resistance or dynamic separation of the contacts due to high short circuit
currents can cause the welding of the contacts. The welding then may
cause a device failure if the device specific opening forces cannot break
the weld connection.
*'''Arc movement''' happens when during the break operation a sufficiently high
magnetic field is generated which exerts a force on the electrical arc which is
then moved from the originating spot towards an arc chute (or arc splitting
plates).
*'''Arc extinguishing''' means the process of letting the current go to zero and
transferring the arcing gap from a conducting to the non-conducting stage.
Selecting the most effective extinguishing measures depend mostly on the
current characteristics, the current value and the circuit voltage.
*'''Recovery''' of an arc gap during contact opening is defined as the process of
the electrically conducting plasma of an arc losing its electrical conductivity after
reaching current-zero.
*'''Symbole used'''
bild
===6.4.2 Contact Physics – Formulas===