Glossary Of Terms and Switch-related Abbreviations

Switch Glossary of Terms

Here is a handy glossary of terms for the switch industry, including explanations of switch abbreviations.

Actuator: The mechanical interface between the basic switch contacts and the means of operation, such as the operator’s finger.

Actuation Force: The required force to change a circuit’s electrical state.

Alternate Action Switch: A pushbutton style switch where the change of the electrical state is maintained between actuations.

Ampere: A unit of electrical current flow.

Base (Housing): The main member to which the conducting parts or insulator unit are attached. It may also have parts of the operating or control mechanism attached.

Bounce: Rebounding of moving contact against fixed contact during transfer.

Break: Interruption of a circuit. Double-break occurs when a single mechanism interrupts two contacts simultaneously.

Break Before Make: The term given to a double throw circuit where the first circuit is opened before the second circuit is closed.

Capacity: Usually refers to the current handling capability of a switch.

Chatter: Rapid opening and closing of contacts, usually exhibited during extreme vibration and/or shock.

Clearance (Spacing): Distance through air between electrically live parts of opposite polarity or to ground.

Contact: The contact is a conducting part designed to be united by pressure to another conducting part for the purpose of carrying current.

Contact Bounce: Oscillation of the movable contact upon closure of the circuit.

Contact Gap: The minimum distance between the fixed and moveable contacts.

Contact Resistance: The resistance of current flow across closed contacts.

Dead-break: Open circuit condition, usually caused when slowly actuating snap-action switches. Results from low contact pressure or contact lift-off.

Detent: Feature that indicates actuation point has been reached. Can also be referred to as tactile feel.

Dielectric Strength: The ability of an insulating material to resist voltage from arcing across its surface.

Differential: Distance between trip point (or force) and reset point (or force).

Double-break: A mechanism that breaks the circuit at two points simultaneously by means of a “shorting bar” like device.

Double-throw: Contact arrangement that alternately transfers normally open and normally closed circuits.

Dust-tight: Will withstand sand and dust contamination.

Electrical Life: Expected cycle life when switch is operated at full electrical load.

Free Position: Point at which plunger exists in the un-operated condition.

Insulation Resistance: The resistance to current flow of the insulating materials between contacts.

Lever Actuator: A device, hinged or spring type, applied to a basic switch to facilitate its application.

Make Before Break: The term given to a double throw circuit when the second circuit is closed before the first circuit is opened.

Momentary Action Switch: A circuit is continuously closed or opened only when force is applied. The electrical state returns to its normal position when the force is removed.

Normally Closed: A circuit is closed in the normal switch position.

Normally Open: A circuit is open in the normal switch position.

Operating Point: Point at which contacts transfer. Usually measured from the switch mounting holes.

Over Travel: The distance an actuator travels after the circuit is closed.

Pole: The term to denote a completely separate circuit, which passes through a switch at one time.

Pre-travel: The movement of the actuator prior to closing the circuit. Sometimes identical to “Travel to Make”.

Reset Point: Point at which contact resumes normal position. Single-Break: Mechanism that transfers one contact.

Single Throw Switch: The circuit can be opened or closed by moving the switch blade into or out of one set of contacts only.

Snap Action: The abrupt transfer of contacts from one position to another. This action is relatively independent of the speed of actuator travel.

Splash-proof: Will withstand heavy rain or stream of water.

Switch: A device for making, breaking, or changing the connections in an electric circuit.

Throw: The term denotes the number of positions in which a given pole is closed.

Travel to Make: The distance parallel to the designated direction of the actuator movement at which point a circuit is closed.

Watertight: Will withstand submersion to various depths depending on specification level.

Wiping Action: Lateral travel of movable contact over fixed contact while pressure between the two contacts exists. Occurs during plunger travel. This action helps clean the contacts of contamination.

Switch Abbreviations

N.C.: Normally Closed circuit

N.O.: Normally Open circuit

SPST: Single Pole Single Throw

SPDT: Single Pole Double Throw

DPST: Double Pole Single Throw

DPDT: Double Pole Double Throw

MBB: Make Before Break

BBM: Break Before Make