ASTM B542-13(2019)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B542 − 13 (Reapproved 2019)
Standard Terminology Relating to
Electrical Contacts and Their Use
This standard is issued under the fixed designation B542; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope arc discharge—a self-sustaining, high current density, high
temperature discharge, uniquely characterized by a cathode
1.1 The terms included in this list are those that are peculiar
fall nearly equal to the ionization potential of the gas or
to electric contacts or general terms that have a specific
vapor in which it exists.
meaning when related to electric contacts.The definitions were
prepared assuming that the reader has a general knowledge in
arc, anode—the arc that occurs at less than a critical electrode
a physical science but is unfamiliar with the terminology of the
spacing (see arc, cathode), and results in anode material
literature of electric contacts.
loss.
1.2 This international standard was developed in accor-
arc, cathode—the arc that occurs at greater than a critical
dance with internationally recognized principles on standard-
electrode spacing (see arc, anode), and results in cathode
ization established in the Decision on Principles for the
material loss.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
arc, shortest—a limiting state of an arc in which the total arc
Barriers to Trade (TBT) Committee.
voltage approaches the sum of the cathode and anode falls.
blowout—the displacement and lengthening of an arc to
2. Significance and Use
facilitate its extinction. The blowout effect can be achieved
2.1 The terms in this standard are used in standards and
by a magnetic field, air blast, etc.
literature related to electric contacts, materials for electric
contacts and test methods for evaluating electric contacts.
brush—a sliding contact member consisting of one or more
These terms may be difficult to locate in a general purpose
sliders (see sliders).
dictionary or the definition in such a dictionary may not cover
cathode fall—the potential difference between the cathode and
the meaning applied in the field of electric contacts.
the electric discharge plasma.
3. Terminology
cathodic (cathode) material transfer—see material transfer.
constriction resistance—the increase in resistance arising
a-spot—the areas of two mating contacts through which
from a change in current density distribution. In electric
current flows from one contact to the other.
contacts it is that portion of contact resistance resulting from
activation—aprocessinwhichcontaminationofthesurfaceof
the convergence of current into the a-spots.
contacts causes arcing at lower than usual voltage or arcing
contact, n—(a) a generic term that applies to a device or part
persists at lower than usual current, or both. For example,
palladium contacts operated in an organic vapor produce of a device and that has the capability of completing or
interrupting the flow of an electrical signal in a circuit, (b)
arcs at voltage and current less than the minimum arcing
voltage and current because of the presence of carbon on the may also be used with modifiers such as: electrical contact,
arcing contact, noble metal contact, separable contact, etc.
contact surfaces.
anode fall—the potential difference between the anode and the contact, adj—contact area, the part of an electrical device that
electrical discharge plasma.
is actually touching and where the electrical signal is
expected to pass. Contact member, one of the electrical path
anodic (anode) material transfer—see material transfer.
parts that can make or break an electrical path.
contact, arcing—an electrical contact whose primary mode of
This terminology is under the jurisdiction of ASTM Committee B02 on
wearout occurs on the contacting surfaces as a result of an
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
arc formed between separating or closing contact pairs.
B02.05 on Precious Metals and Electrical Contact Materials.
Current edition approved Nov. 1, 2019. Published November 2019. Originally
contact bounce—the unwanted operation of contacts immedi-
approved in 1932. Last previous edition approved in 2013 as B542 – 13. DOI:
10.1520/B0542-13R19. ately following intentional operation.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B542 − 13 (2019)
contact(s), butting—a type of contacts in which the direction corona (discharge)—a self-sustaining discharge characterized
of the motion of the moving contact is perpendicular to the by highly asymmetrical electric fields with the result that
contact faces. The contacts close and open with no appre- ionization predominantly occurs near the electrode with the
ciable sliding or rolling action. higher potential gradient.
contact chatter—the unwanted operation of contacts resulting
crimp, v—to establish an electrical and mechanical attachment
from external forces operating on them. For example,
between the two members by mechanically deforming one
vibration may cause contacts to open and close or “chatter.”
contact member around another. In most cases, one member
is a stranded or solid wire, or a group of wires, the other is
contact-closing force—the transient force between contacts
a hollow cylinder or partial cylinder that is deformed around
during closure. At the first instant of closure this force is
the wire(s).
zero. It then builds up to a maximum value dependent on the
forces and inertia of the contact system and finally stabilizes
dark (or Townsend) discharge—a discharge which may or
at the static contact force.
may not be self-sustaining. It is characterized by a uniform
field, current in the microampere range, and a nonluminous
contact, composite—a contact made of two or more distinct
inter-electrode space.
materials or alloys bonded to each other. For example, a
contact with a facing of a precious metal bonded to a
electromigration—(1) Current-induced atomic diffusion in a
base-metal backing.
solid metal due to electron momentum and the potential
contact force—the force to close, maintain, or open contacts.
gradient, (2) electrochemical process of growth of metallic
See also insertion force, withdrawal force, and normal path across an insulating surface under imposed electric
force.
field.
DISCUSSION—The solid state process may cause significant material
contact noise—a varying voltage across a pair of electric
transport in regions of high current density such as a-spots in contacts.
contacts due to conditions at their interface.
In devices with electrical contacts, the electrochemical process may
form shorts between conductors under certain environmental condi-
contact, non-arcing—mating electrical contact surfaces that
tions.
do not experience wearout due to arc erosion that is opposite
of arcing contacts.
film resistance—that portion of the contact resistance that is
due to the presence of contaminants on one or both of the
contact, pitted—a contact that has numerous discrete hollows
contact members.
in its surface.
contact pressure—the force per unit area of physical contact fine transfer—see material transfer, bridge.
betweentwocontacts.Thistermisfrequentlybutimproperly
fretting, n—small amplitude oscillatory motion, usually
used when contact force is meant. The area of physical
tangential, between two solid surfaces in contact.
contact is usually difficult to determine and quite different
DISCUSSION—Here the term fretting refers only to the nature of the
from the apparent area of contact.
motion without reference to the wear, corrosion, or other damage that
may ensue.The term fretting is often used to denote fretting corrosion
contact resistance—the resistance to current flow offered by
and other forms of fretting wear. Usage in this sense is discouraged
the contact interface, comprising the sum of the constriction
because of the ambiguity that may arise.
resistance plus the film resistance.
fretting corrosion—a form of fretting wear in which corrosion
NOTE 1—In a practical measurement, correction must be made for bulk
plays a significant role.
resistance consisting of contact material, lead wires, etc.
DISCUSSION—In electrical contact interfaces involving non-noble
contact, screw—a contact fabricated with an external thread
metals, fretting corrosion can cause rapid and substantial increases in
for attachment to a support member or for adjustment. contact resistance as a result of localized appearance of insulating
oxides and other corrosion products at the interface.
contact, sliding—an electric contact which is expected to do
its primary function during sliding. fretting wear—wear arising as a result of fretting. See
fretting.
contact, solid—a monolithic contact member.
friction polymerization—the process by which organic com-
contact, spring—a contact system in which one piece of
pounds (such as adsorbed air pollutants) on mating surfaces
material is used for both the driving spring and electric
that move relative to each other polymerize to yield com-
contact.
pounds of high molecular weight.
contact, static—an electric junction designed for infrequent
NOTE 2—When this occurs on electrical contacts and the materials
separation and connection.
formed remain on the surface, contact resistance may increase substan-
contacts, wiping—contacts that have some sliding motion tially. The solid materials that are produced by the polymerization process
are called “friction polymers” or “frictional polymers.”
during opening or closing.
contact wipe—relative tangential motion between contacting fritting (A-fritting)—an electric breakdown between mating
surfaces that occurs during the normal course of contact metallic contacts, separated by an insulating film, which
closure. occurs when the field strength exceeds approximately
B542 − 13 (2019)
1 000 000V/cm. Metallic bridges are produced through the showering—a particular form of corona discharge character-
film if the fritting voltage is above the contact melting ized by strongly ionized streamers or streams of luminous
voltage. plasma. It generally occurs at a field value just below that
which is required for a complete breakdown.
fritting voltage—the voltage at which fritting occurs.
slider—that member of a sliding contact pair, normally the
glow discharge—a self-sustaining discharge characterized by
smaller, which may be moved through a range of locations
essentially symmetrical electrodes, low current density, and
on the opposing member.
a high cathode fall of about 200 V.
sliding electrical contacts—contacting members that perform
glowing connecti
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