ASTM B542-04
(Terminology)Standard Terminology Relating to Electrical Contacts and Their Use
Standard Terminology Relating to Electrical Contacts and Their Use
SCOPE
1.1 The terms included in this list are those that are peculiar to electric contacts or general terms that have a specific meaning when related to electric contacts. The definitions were prepared assuming that the reader has a general knowledge in a physical science but is unfamiliar with the terminology of the literature of electric contacts.
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Designation:B542–04
Standard Terminology Relating to
1
Electrical Contacts and Their Use
This standard is issued under the fixed designation B 542; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope arc, shortest—a limiting state of an arc in which the total arc
voltage approaches the sum of the cathode and anode falls.
1.1 The terms included in this list are those that are peculiar
blowout—the displacement and lengthening of an arc to
to electric contacts or general terms that have a specific
facilitate its extinction. The blowout effect can be achieved
meaning when related to electric contacts.The definitions were
by a magnetic field, air blast, etc.
prepared assuming that the reader has a general knowledge in
brush—a sliding contact member consisting of one or more
a physical science but is unfamiliar with the terminology of the
sliders (see sliders).
literature of electric contacts.
cathode fall—the potential difference between the cathode and
2. Significance and Use
the electric discharge plasma.
cathodic (cathode) material transfer—see material transfer.
2.1 The terms in this standard are used in standards and
constriction resistance—the increase in resistance arising
literature related to electric contacts, materials for electric
from a change in current density distribution. In electric
contacts and test methods for evaluating electric contacts.
contacts it is that portion of contact resistance resulting from
These terms may be difficult to locate in a general purpose
the convergence of current into the a-spots.
dictionary or the definition in such a dictionary may not cover
contact, n—a) a generic term that applies to a device or part of
the meaning applied in the field of electric contacts.
a device and that has the capability of completing or
3. Terminology
interrupting the flow of an electrical signal in a circuit. b)
may also be used with modifiers such as: electrical contact,
a-spot—the areas of two mating contacts through which
arcing contact, noble metal contact, separable contact, etc.
current flows from one contact to the other.
contact, adj—contact area, the part of an electrical device that
activation—aprocessinwhichcontaminationofthesurfaceof
is actually touching and where the electrical signal is
contacts causes arcing at lower than usual voltage or arcing
expected to pass. Contact member, one of the electrical path
persists at lower than usual current, or both. For example,
parts that can make or break an electrical path.
palladium contacts operated in an organic vapor produce
contact, arcing—an electrical contact whose primary mode of
arcs at voltage and current less than the minimum arcing
wearout occurs on the contacting surfaces as a result of an
voltage and current because of the presence of carbon on the
arc formed between separating or closing contact pairs.
contact surfaces.
contact bounce—the unwanted operation of contacts immedi-
anode fall—the potential difference between the anode and the
ately following intentional operation.
electrical discharge plasma.
contact(s), butting—a type of contacts in which the direction
anodic (anode) material transfer—see material transfer.
of the motion of the moving contact is perpendicular to the
arc discharge—a self-sustaining, high current density, high
contact faces. The contacts close and open with no appre-
temperature discharge, uniquely characterized by a cathode
ciable sliding or rolling action.
fall nearly equal to the ionization potential of the gas or
contact chatter—the unwanted operation of contacts resulting
vapor in which it exists.
from external forces operating on them. For example,
arc, anode—the arc that occurs at less than a critical electrode
vibration may cause contacts to open and close or “chatter.”
spacing (see arc, cathode), and results in anode material loss.
contact-closing force—the transient force between contacts
arc, cathode—the arc that occurs at greater than a critical
during closure. At the first instant of closure this force is
electrode spacing (see arc, anode), and results in cathode
zero. It then builds up to a maximum value dependent on the
material loss.
forces and inertia of the contact system and finally stabilizes
at the static contact force.
1
This terminology is under the jurisdiction of ASTM Committee B02 on contact, composite—a contact made of two or more distinct
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
materials or alloys bonded to each other. For example, a
B02.91 on Terminology.
contact with a facing of a precious metal bonded to a
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