Glossary

A comprehensive list of key words used in the industry.

Active Area (contact): Electrical junction comprising a multitude of contact a- spots through which electrical current passes from one connector component to the other.

Actuation Force: The force required to change a switch actuator from one position to another. Measured exactly when switch changes state.

Actuator: A movable part of a switch which causes a change in the electrical configuration of the switch.

Actuation: Operating or releasing a switch by depressing or releasing its actuator or rotating its shaft.

Air Gap: The minimum distance between separated mating contacts in their fully open position.

Alternate Action: A pushbutton switch style in which the electrical state of the switch is maintained between actuations of the plunger.

Alternating Current: A current, the direction of which reverse at regularly recurring intervals.

Ambient: Surrounding operating conditions external to the switch. This includes physical atmosphere, as well as the form and nature of applied electrical and mechanical loads.

American Wire Gauge: A standard system used for designating the size of electrical conductors. Abbreviated AWG. Based on specified ranges of circular mil area. American Gauge numbers have an inverse relationship to size.

Ampere: A unit of electrical current.

Antistatic Switch: An antistatic switch will withstand a specified potential without conducting between the actuator and any conducting element, usually terminal or bushing.

Arc: Gaseous electrical discharge between separated contacts of a switch, involving a stream of electrons, metal vapors and ions.

AWG: A standard system used for designating the size of electrical conductors. Abbreviated AWG. Based on specified ranges of circular mil area. American Gauge numbers have an inverse relationship to size.

Bifurcated Contact: A wiping movable contact consisting of spring fingers that grip the fixed contact.

Break: An interruption in a circuit. Denotes the number of pairs of separated contacts the switch introduces into each circuit it opens.

Butt Contact: A contact mechanism in which the movable contact makes contact with the stationary contact without wiping motion between the surfaces. Typical of toggle and pushbutton switches.

Cadmium Oxide: A compound added to silver to make it more able to resist welding.

Conductive Rubber: Elastomer filled with carbon or metallic particles which render the material electrically conductive.

Contact: The component of the switch that disengages to cause the actual circuit interruption.

Contact Configuration: Poles, throws, and sequence designated by alpha characters.

Contact Pressure: The amount of force holding the movable and stationary contacts together. While this should be termed Contact Force, by convention in the United States, it is called Contact Pressure.

Contact Resistance: The junction resistance between 2 contacts. Usually measured at contact terminals. It is the total resistance provided by the Construction and Film Résistances.

Contact Wipe: Sliding of one contact on another during actuation of switch.

CSA: Canadian Standards Association.

Current-Carrying Capacity: Specified maximum current which can flow through the switch contacts. Determined by contacts size, shape, material and the force with which they are pressed together.

Current Rating: The nominal or name plate current capacity of a device. The maximum current rating, listed by UL, is the current that can be carried continuously without causing the temperature of the switch terminals to rise more than 30 C above the ambient temperature.

Cycle: The complete program of operations required to return switch to the same condition that existed at the beginning of the cycle.

Contacts: Switch element, which directly provide make-break operation (circuit interruption).

Detent: A mechanism intended to hold actuator and contacts in the fixed position after the actuation forced is removed or reduced to less than specified value. It also identifies actuator position by means of tactile feel.

Dielectric: Non-conductive material, electrical isolation.

Dielectric breakdown: Rupture of insulating material when the electric stress exceeds the dielectric strength of the material (Voltage Breakdown).

Dielectric strength: A specific voltage that a switch can withstand without leakage current between insulated conductors. Most often applies to insulator between switch terminals and metal exposed to operator of the switch.

DIP: Dual-in-line package refers to a component with two rows of PC terminals. The terminals most commonly have pitch of 0.100 and located at 0.30 across the package.

Dome: Dome-shaped metal elastomer switch component used as tactile element/return spring.

Dry Circuit: Low power level or Logic circuit. Power levels do not cause arcing, melting or softening of contacts.

D.W.V.: Dielectric Withstanding Voltage.

Electrical Life: Life of a switch (number of operations) under a specified combination of electrical load, actuation, environment, and criterion of failure.

EMC: Electro-Magnetic Compatibility.

EMI: Electro-Magnetic Interference.

Erosion, Contact: The transfer or vaporization of contact material resulting from the arc due to breaking or opening the circuit.

ESD: Electrostatic discharge, the static charge that is built up that can amount to several thousand volts. Can destroy electronic components.

Form A: A single pole, single throw, normally open contact or SPST NO.

Form B: A single pole, single throw, normally closed contact or SPST NC.

Form C: A single pole, double throw contact or SPDT.

Force, Contact: The force, holding closed contact together.

Gap: The shortest straight-line distance between two separate contacts.

Ground: Used to indicate a negative side or ground side of a battery or electrical supply (ac or dc).

Hall effect: A voltage generated across a current carrying conductor, when the conductor is placed in a magnetic field.

Heat Rise: An indirect measurement of a contact resistance used by rating agencies. The temperature rise of a contact carrying a prescribed current is measured to determine acceptable limit.

Horse power, HP: Unit of power. 1 HP=736 W=0.36 kW

Horse Power Rating: UL switch rating for the adequate motor load. Intended to simulate lock rotor conditions. Typical HP rating is 1/4HP, 1/2HP, 3/4HP, 1 HP at the nominal voltage. Switch is tested with specified current for the specified number of cycles; e.g. 1/4 HP tested with 35A current for 50 cycles.

Housing: A three dimensional enclosure, a container for a switch.

Hz: Unit of measure of frequency. Reciprocal of time period: 1 Hz= 1/sec

Inrush current: Current that drawn by electrical motor during start-up transitioning or by a lamp filament during heating to its operating resistance.

Insulation Resistance: The electrical resistance between two normally insulated parts; measured at a specific high potential (1000 Vrms). Typical value for switches is 1 G.

Life Electrical: The life of a switch, controlling a specified electrical load.

Life Mechanical: The number of cycles of operation that a switch will perform with no voltage applied to the contacts.

Make: Indicates that a switch has completed the dynamics of closing an electrical circuit.

Make & Break Contacts: Contacts that make/break current flow. They are differentiated from those that operate principally in a sliding mode.

Make-before-Break: The moving contact establishes a new circuit before interrupting the circuit previously established, while transferring to another position.

Momentary Action: The circuit is either opened, or closed, only as long as the switch is actuated.

Non-shorting contacts: Break-before-make.

Normally Closed: A term used to describe contacts which establish a circuit when in the normal position.

Normally Open: A term used to describe contacts which interrupt the circuit when in their normal position.

Passive components: Components which have no gain characteristics, such as capacitors and resistors.

Shorting Contacts: Make-before-break. Referred to rotaries and slides.

Sliding Contact: Contacts that make or interrupt current flow by means of tangential motion (rotary, slip ring).

Slow make-slow break: Purposely designed switch mechanism (“see–saw” type) with relatively slow operation to provide a slight time delay, permitting the ac wave to go through its zero energy level (natural current zero duration is 8.35 msec).

Pitch: The spacing between centers of adjacent leads.

Pole: The number of completely separate circuits that can pass through the switch at one time.

Resistance, electrical: Ability of the element, component, conductor or a system to obstruct current flow.

Resistance, insulation: Resistance of electrical isolator between two electrodes, defined by Ohms Law as result of division of the applied voltage and measured current. Not to be confused with dielectric strength.

Resistivity: (specific resistance:) property of material that impedes electrical current when a sample of specified unit dimensions is considered.

Surface Mounting (SMT): A method of soldering packages directly onto the surface of printed-circuit boards without insertion of the leads through hole in the board.

Switch Abbreviations: SPST: Single-pole single-throw; SPDT: Single-pole double-throw; DPST: Double-pole single-throw; DPDT: Double-pole double-throw.

Throw: Denotes the number of different circuits that each individual pole can control.

Total Travel: The sum of pretravel and overtravel for snap-and push-button switches.

Truth Tables: The output code or connection sequence from a thumbwheel switch.

UL: Underwriters Laboratories.

VDE: Verdband Dentscher Electrotechniker Germany’s equivalent to USA Underwriters’ Laboratories.

Voltage Drop: Change in voltage that results from a current passing through a device. For switches Voltage drop is typically referred as Contact drop DV.

Wiping contact (action): Lateral travel of movable contact over fixed contact while pressure between the two contacts exist. The action helps clean the contacts of contamination and oxidation film. It is very important in low energy circuits applications.