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Glossary

Assemblage   A specific physical arrangement of blades and terminals grouped to form a single pole of contacting. Assemblages (called Circuits in snap switches) are usually designated by a number. The most popular Assemblages by far are Ass. 2 and Ass. 3.

Break   When a contact opens and current cannot flow that contact is said to Break.

Break Before Make   Abbreviated as BBM, this refers to a contact designed to open before contacts in adjacent positions close. This is the most common type of contact and BBM switches generally have all contacts open between positions. Also called "Non-shorting".

Cam   Any of a group of Industrial Switches in which the contacts are controlled by the action of a mechanical follower moving over the contoured surface of a "cam" or plastic disk affixed to and rotated by the handle shaft. The surface contours of the individual cams are chosen to provide the needed contact action. Electroswitch cam switches are the 20K [utility] and KW [ind] families.

Continuous   In electrical ratings, "Continuous" refers to the maximum current flow possible through a given closed contact that will not damage or compromise the useful life of that contact. The rating is generally a function of the physical size of the conductors used and implies no making or breaking of the contact under load.

Detent   Specifically, a detent is the spring and starwheel mechanism that holds the switch in a selected position. More generally, we use the term "Detent Switches" to refer to any of the family of industrial, utility or military blade switches such as Series 24, 31, 25, AF, or SJR. Cam Switches and Snap Switches are not Detent Switches.

Escutcheon   See Nameplate

Form A Contact   A normally open contact. It must be operated to close.

Form B Contact   A normally closed contact. It must be operated to open.

Form C Contact   A single pole, double throw [SP/DT or 1P/2T] contact

Indexing   The angle between handle positions. Can be 45 [maximum of 8 positions], 30 [max 12], 90 [max 4] or many others. Dividing 360 by the maximum number of positions yields the indexing angle. Dividing 360 by the indexing angle gives the maximum number of positions. Not all indexing angles are available on all switches.

Interrupting   In electrical ratings, "interrupting" usually designates the highest current at which a contact can be opened "under load" [while current is flowing] without compromisinging published life expectancy of the switch. Due to the destructive effects of arcing, this the most strenuous type of operation for a contact and Interrupting ratings are generally lower than Continuous ratings for a given contact type.

Latching   In a relay, latching refers to the ability to move contacts into a specific state [open or closed] upon command and have them then remain in that state when the command is removed. Some subsequent action or command is usually required to move the contacts back to the prior state.

Maintained   Unlike Spring Return or Momentary switches, Maintained switches remain in position when the handle is released.

Make   When a contact closes making it possible for current to flow, that contact is said to Make.

Make Before Break   Abbreviated as MBB, this refers to a contact that is designed to "Make" or close before another contact in an adjacent position can "Break" or open. Also called "Shorting" or "Overlapping" contacts, MBB contacts are most often used in ammeter, current transformer and other applications where it is important that current flow not be interrupted while the position of the switch changes.

Making Ability   The maximum amount of current that a given contact can close on without damaging the contact and/or imparing switch life. Useful mostly in Circuit Breaker control operations, Making ability is usually far greater than interrupting ability.

Momentary   When the contacts of a switch or relay are moved to one state [n/o or n/c] and then automatically revert back to the prior state when the stimulus is removed, that is described as momentary contacting. On manual switches, "Spring Return" action refers to momentary contacts.

Nameplate   The front plate provided with many switches on which can be engraved or stamped words designating the function of the switch [title engraving] and/or the functions of each handle position {position engraving]. Usually mounted on the front of the panel behind the handle, the nameplate can also be called an Escutcheon, Designation Plate or Title Plate.

Non-shorting   Another term for Break Before Make contacting.

Normally Closed   Also called a Form B contact, this refers to a contact that is closed whenever the switch handle is moved to what is considered to be the "Normal" position. Often abbreviated as n/c. This term is most useful and unambiguous in switches limited to two positions.

Normally Open   Also called a Form A contact, this refers to a contact that is open whenever the switch handle is moved to what is considered to be the "Normal" position. Often abbreviated as n/o. This term is most useful and unambiguous in switches limited to two positions.

Overload Current   A measurement of the maximum current flow possible in a given closed contact for a specified short time. Experiencing this current level may or may not compromise the life of a contact.

Pole   On a switch, each independent electrical circuit is called a Pole. The number of Poles is usually equal to the number of discrete inputs on the switch. The term "Pole" is usually used in conjunction with "Throw". For example, the phrase "Six Pole/Double Throw with Off" describes a switch with 6 electrically independent circuits fed through 2 active handle positions and an Off position.

Shorting   Another term for Make Before Break contacting.

Snap   Any of the family of switches that utilize the Snap Drive mechanism. Examples are the Series 101, 103, 105, 1SR and 20SR among others. As Snap switch handles are rotated, a spring is wound. When the handle reaches 120 the blade is released to move 90 at high speed and make or break the circuit. The speed of the snap switch action makes it very effective for interrupting large DC currents.

Target   A colored indicator on a nameplate that is used to show the last active position into which the switch handle was moved. Usually seen on spring return Breaker Control switches where Red [denoting the Close position] and Green [Trip] are the typical colors used. Lockout Relays use a nameplate with an Orange target flag to indicate a Tripped LOR.

Throw   On a switch, the number of "throws" is usually the same as the number of handle positions producing a discrete output. This term is usually used in conjunction with "pole" as in "Double Pole/Double Throw", "Six pole/Five Throw", or "Three Pole/Five Throw with Off". Often abbreviated as "DP/DT", "2P/4T ", etc.