| Aisle
| Part of a sheltered aisle switchgear installation. Connected accessway for multiple vertical enclosures in an outdoor installation. Weatherproof access doors are normally supplied at both ends of the aisle. |
| ANSI
| American National Standards Institute. It was organized to simplify and standardize production and construction. |
| Arc-Resistant
| A special certification that equipment must have for use in certain circumstances. The design of arc-resistant equipment is dedicated to the safe control and release of arc-related overpressures. |
| Automatic Shutter System
| Circuit breaker compartment safety feature. When the circuit breaker is removed from its compartment, the compartment’s fixed primary conductors are automatically covered to prevent contact with live primary current-carrying parts. |
| Auxiliary Compartment
| An optional compartment in a medium voltage switchgear assembly, usually located above or below a circuit breaker compartment. Used when there is a significant volume of auxiliary and/or control equipment required in the assembly. |
| Bus Joint
| The connection between the main bus and a circuit breaker (or other devices). Bus joints must be insulated. |
| Circuit Breaker
| A reusable overcurrent protection device. After tripping to break the circuit, it can be reset to protect the circuit again. |
| Circuit Breaker Compartment
| A compartment in a medium voltage switchgear assembly that contains and electrically connects one or more circuit breakers. |
| Common Aisle Switchgear
| An outdoor installation solution for very large assemblies. A variation on sheltered aisle switchgear, in which vertical structures are on both sides of the aisle. |
| Continuous Current
| The amount of current the breaker can carry continuously at 60 cycles without exceeding the temperature rise limit, according to ANSI charts. |
| Control Compartment
| The space between the front of the circuit breaker and the front doors of the assembly. This is where instruments, meters, relays and other control equipment are usually mounted. |
| Control Power Transformer
| A transformer that provides a safe, reasonable low voltage source for relays, contactors and other devices. |
| Extension Rails
| A common feature of the circuit breaker itself. Allow the circuit breaker slide out of its compartment easily for inspection. |
| Feeder Circuit Breaker
| A reusable overcurrent protection device designed to protect a panel downstream from a medium voltage switchgear assembly. |
| Finger Cluster
| A configuration of spring-loaded conductive fingers mounted on the circuit breaker, often made of silver-plated copper. When the circuit breaker is levered into the CONNECTED position, its finger clusters engage the circuit breaker compartment’s stationary primary conductors to make electrical connection. |
| Ground Bus
| A grounded bus that runs the length of the assembly, and is normally located in the lower part of the line compartment. For safety reasons, the ground bus is capable of carrying the rated short circuit current of the installed circuit breakers for a certain amount of time. |
| IEC
| Abbreviation for International Electro-technical Commission. This organization is associated with equipment used internationally. |
| IEEE
| Institute of Electrical and Electronic Engineers. A professional organization of scientists and engineers whose purpose is the advancement of engineering. |
| Lever
| A term to describe the act of moving a circuit breaker from one position to another. |
| Line Compartment
| Space is provided in this compartment for line terminations or other special devices. Assembly designs usually permit entry and/or exit of cable or bus from the top or bottom of the compartment. |
| Main Bus
| A set of electrical conductors, usually three per set. These individually insulated conductors provide for multiple connections into the electrical system. In medium voltage switchgear assemblies, the main bus usually takes the form of solid copper bars. |
| Main Bus Compartment
| A compartment in a medium voltage switchgear assembly through which the main bus runs. |
| Main Circuit Breaker
| Also “Main Breaker.” A reusable overcurrent protection device designed to protect an entire medium voltage switchgear assembly. |
| Medium Voltage Switchgear Assembly
| An integrated assembly of compartmentalized, removable circuit breakers with an insulated main bus, associated control devices, and auxiliary equipment designed to provide medium voltage circuit protection |
| Metal-Clad
| Equipment in the assembly is enclosed, and separated by metal barriers into individual compartments. Typically associated with medium voltage equipment. |
| Metal-Enclosed
| Equipment in the assembly is enclosed, but not necessarily separated by barriers. Typically associated with low voltage equipment. |
| NEMA
| Abbreviation for National Electrical Manufacturers Association. An organization of manufacturers of electrical products. |
| Outdoor Aisle-less Switchgear
| An outdoor installation solution. Basically, the assembly of a weatherproof enclosure around an indoor switchgear assembly. |
| Outdoor Control Room
| An outdoor installation solution. Encloses all the equipment in one weatherproof house. Normally, the construction takes place at the manufacturer’s location and then moved to the installation site |
| Safety Interlock
| A feature of both the circuit breaker compartment and the circuit breaker itself. Helps ensure safe and proper interfacing between the circuit breaker and its compartment. Interlocks are required by governing standards, and must be supplied by all manufacturers. |
| Seismically-Qualified
| A special certification that equipment must have for use in certain earthquake-prone zones. |
| SF
6 | An arc extinguishing technology involving the use of sulfur hexafluoride gas. |
| Sheltered Aisle Switchgear
| An outdoor installation solution. An outdoor enclosure is constructed around an indoor switchgear assembly with an aisle constructed as part of the enclosure at the front of the assembly. |
| Surge Arrester
| A device that protects equipment from electrical surges. |
| Switchgear
| An assembly of switching and interrupting devices, along with control, metering, protective and regulating equipment. |
| Vacuum Interrupter
| An arc extinguishing technology. Features a pair of separable contacts enclosed in a vacuum-tight envelope. Because the environment inside the interrupter envelope is a vacuum, an arc cannot be sustained easily. |
| Vertical Structure
| A metal enclosure for the other switchgear components. A switch gear assembly can consist of practically any number of adjacent vertical structures. |
| Voltage Transformer
| Also “potential transformer.” A step-down transformer that steps down supplied voltage to a voltage usable by control components such as relays and meters. |
