ASTM B542-00
(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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B 542 – 00
Standard Terminology Relating to
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—a process in which contamination of the surface of
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.
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 Editorial and Terminology.
contact with a facing of a precious metal bonded to a
Current edition approved Oct. 10, 2000. Published January 2001. Originally
base-metal backing.
published as B 542 – 32 T. Last previous edition B 542 – 99
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B542–00
contact force—the force to close, maintain, or open contacts. fretting, n—small amplitude oscillatory motion, usually tan-
See also insertion force, withdrawal force, and normal gential, between two solid surfaces in contact.
force.
DISCUSSION—Here the term fretting refers only to the nature of the
contact noise—a varying voltage across a pair of electric
motion without reference to the wear, corrosion, or other damage that
contacts due to conditions at their interface.
may ensue. The term fretting is often used to denote fretting corrosion
contact, non-arcing—mating electrical contact surfaces that and other forms of fretting wear. Usage in this sense is discouraged
because of the ambiguity that may arise.
do not experience wearout due to arc erosion that is opposite
of arcing contacts.
fretting corrosion—a form of fretting wear in which corrosion
contact, pitted—a contact that has numerous discrete hollows
plays a significant role.
in its surface.
DISCUSSION—In electrical contact interfaces involving non-noble
contact pressure—the force per unit area of physical contact
metals, fretting corrosion can cause rapid and substantial increases in
between two contacts. This term is frequently but improperly
contact resistance as a result of localized appearance of insulating
used when contact force is meant. The area of physical
oxides and oter corrosion products at the interface.
contact is usually difficult to determine and quite different
fretting wear—wear arising as a result of fretting. See
from the apparent area of contact.
fretting.
contact resistance—the resistance to current flow offered by
friction polymerization—the process by which organic com-
the contact interface, comprising the sum of the constriction
pounds (such as adsorbed air pollutants) on mating surfaces
resistance plus the film resistance.
that move relative to each other polymerize to yield com-
NOTE 1—In a practical measurement, correction must be made for bulk
pounds of high molecular weight.
resistance consisting of contact material, lead wires, etc.
NOTE 2—When this occurs on electrical contacts and the materials
contact, screw—a contact fabricated with an external thread
formed remain on the surface, contact resistance may increase substan-
for attachment to a support member or for adjustment. tially. The solid materials that are produced by the polymerization process
are called “friction polymers” or “frictional polymers.”
contact, sliding—an electric contact which is expected to do
its primary function during sliding.
fritting (A-fritting)—an electric breakdown between mating
contact, solid—a monolithic contact member.
metallic contacts, separated by an insulating film, which
contact, spring—a contact system in which one piece of
occurs when the field strength exceeds approximately
material is used for both the driving spring and electric
1 000 000 V/cm. Metallic bridges are produced through the
contact.
film if the fritting voltage is above the contact melting
contact, static—an electric junction designed for infrequent
voltage.
separation and connection.
fritting voltage—the voltage at which fritting occurs.
contacts, wiping—contacts that have some sliding motion
glow discharge—a self-sustaining discharge characterized by
during opening or closing.
essentially symmetrical electrodes, low current density, and
contact wipe—relative tangential motion between contacting
a high cathode fall of about 200 V.
surfaces that occurs during the normal course of contact
high resistance—contact resistance exceeding an arbitrary,
closure.
specified limit.
corona (discharge)—a self-sustaining discharge characterized
inrush current—a transient current that exists at the instant of
by highly asymmetrical electric fields with the result that
contact closure and persists for a relatively short time.
ionization predominantly occurs near the electrode with the
insertion force—the force required to mate two connector
higher potential gradient.
halves.
dark (or Townsend) discharge—a discharge which may or
material transfer—a general term to describe the carry-over
may not be self-sustaining. It is characterized by a uniform
of material from one electrical contact to another.
field, current in the microampere range, and a nonluminous
NOTE 3—When the discussion becomes specific, the term “gain” or
inter-electrode space.
“loss” is used with respect to a particular contact (for d-c application,
electromigration—(1) Current-induced atomic diffusion in a
anode or cathode; for a-c application, stationary contact or movable
solid metal due to electron momentum and the potential
contact). For example, anode gain, anode loss, stationary contact gain.
gradient, (2) electrochemical process of growth of metallic
material transfer, negative—see material transfer.
path across an insulating surface under imposed electric
material transfer, positive—see material transfer.
field.
material transfer, bridge—material transfer that occurs with-
DISCUSSION—The solid state process may cause significant material
out the presence of a gaseous electric discharge. The filament
transport in regions of high current density such as a-spots in contacts.
of molten contact material that connects the two separating
In devices with electrical contacts, the electrochemical process may
contacts does not rupture in the middle; thus there is a gain
form shorts between conductors under certain environmental condi-
of material on one co
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.