| ANSI
| American National Standards Institute. It was organized to simplify and standardize production and construction. |
| Arc
| The effect generated when current is forced to be interrupted between two contacts. |
| Arc Chute
| A component of the arc extinguisher in a low voltage circuit breaker. It elongates and cools an arc. |
| Arc Extinguisher
| A component of a circuit breaker. It actually interrupts the flow of current. |
| Circuit Breaker
| A reusable overcurrent protection device. After tripping to break the circuit, it can be reset to protect the circuit again. |
| Continuous Current
| The amount of current the breaker can carry continuously at 60 cycles without exceeding the temperature rise limit, according to ANSI charts. |
| Current Transformer
| A step-down transformer that steps down supplied current to a current usable by control components such as relays and meters. |
| Current Zero
| Also “Zero Point.” A point in the AC current sine wave where the value is zero. |
| Dielectric
| The insulating medium between two contacts. Typical dielectrics are air, gas, ceramic or gas and ceramic. A vacuum is the only perfect dielectric. |
| Dielectric Strength
| The maximum voltage a dielectric can withstand without breaking down. |
| Drawout Mount
| A mounting type for medium voltage power circuit breakers in which the breaker can be completely removed from its compartment onto integral extension rails. |
| Envelope
| Main component of a vacuum interrupter. A sealed, evacuated ceramic enclosure, with a metal end plate brazed to each end. |
| Fixed Mount
| A mounting type for medium voltage power circuit breakers in which the breakers are fixed in place. Usually found in outdoor applications. |
| Frame
| A component of a medium voltage power circuit breaker. Its primary function is to provide a rigid, mechanically strong, insulated housing in which the other components are mounted. |
| 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. |
| Magnetic Air Type Circuit Breaker
| A type of medium voltage power circuit breaker no longer in common use. |
| Maximum Voltage
| The highest voltage at which the breaker can operate, according to ANSI charts. The operating voltage where the circuit breaker is applied should not exceed the circuit breaker’s rated maximum voltage. |
| Medium Voltage Power Circuit Breaker
| A specific type of circuit breaker, used in a switchgear assembly, with a voltage range of 1000 volts to 38 kV. |
| Metal-Clad Assembly
| Equipment in the assembly is enclosed, and separated by metal barriers into individual compartments. Typically associated with medium voltage equipment. |
| Metal-Enclosed Assembly
| 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. |
| Normal Current
| The amount of current the breaker can carry continuously at 60 cycles without exceeding the temperature rise limit, according to IEC charts. |
| Operating Mechanism
| Opens and closes the contacts of a circuit breaker. |
| Panelboard
| A wall-mounted electrical power distribution device for use in commercial and industrial applications. It provides circuit control and overcurrent protection for light, heat or power circuits. |
| Protective Relay
| The specific trip unit used with a medium voltage power circuit breaker. Functions to detect a defective line or apparatus, as well as dangerous or undesirable system conditions. |
| SF
6 | An arc extinguishing technology involving the use of sulfur hexafluoride gas. |
| Short Circuit Current
| A rating of the level of three-phase short circuit current that the circuit breaker can safely interrupt. The short circuit current is a rating at the circuit breaker’s maximum voltage (ANSI) or voltage class (IEC). |
| Switchboard
| A floor-standing electrical power distribution device for use in commercial and industrial applications. It divides large blocks of electrical current into smaller blocks of current used by electrical equipment. |
| Switchgear
| An assembly of switching and interrupting devices, along with control, metering, protective and regulating equipment. |
| Transient Recovery Voltage
| The most severe waveform the vacuum interrupter will have to withstand. |
| Trip Unit
| “brain” of a circuit breaker. |
| UL
| Underwriters Laboratory. An independent laboratory that tests equipment to determine whether it meets certain safety standards when properly used. |
| 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. |
| Voltage Class
| The highest voltage at which the breaker can operate, according to IEC charts. The operating voltage where the circuit breaker is applied should not exceed the circuit breaker’s rated voltage class. |
