1994 Pontiac Grand Am Repair Manual download free. Circuit breakers are used in nearly all electrical systems — from residential dwellings to electric utility facilities. We rely on them to protect our systems from damaging overcurrents and short circuits. Understanding circuit breaker construction and operation is key to realizing their limitations and proper usage. This article covers basic components and operation of popular types of circuit breakers, including molded-case (MCCB), insulated-case (ICCB), low-voltage power (LVPCB), medium-voltage air-magnetic (MVACB), and medium-voltage vacuum (MVVCB) circuit breakers. Key Components MCCBs contain five components — a frame, operating mechanism, interrupting structure, trip unit, and terminal connections. These components are shown in. • • Frame — houses and supports the components and also provides insulation to contain the arc.

• Operating Mechanism — opens and closes the contacts. • InterruptingStructure — includes the arc chutes and all current-carrying parts except the trip unit. Arc chutes are designed to interrupt the arc quickly, usually 1.5 to two cycles for MCCBs and ICCBs. • Trip Unit — senses abnormal current flow and causes the operating mechanism to open the contacts. MCCB trip units are usually of the thermal-magnetic type. • Terminal Connections — provides a suitable connection from the breaker to the conductor.

Molded-case circuit breakers typically bolt directly to the bus. Most manufacturers’ MCCBs have similar components and similar appearance.

ICCBs have the same basic construction as MCCBs, but use solid-state and digital trip units (as opposed to thermal-magnetic trip units) and have much higher interrupting ratings. ICCBs are often draw-out type, as opposed to bolt-in, although they can be either. LVPCBs ( Photo 1 at right) are also known as air-frame and draw-out circuit breakers. download free Yamaha Ttr 225 Manual. There are five major assemblies on a typical LVPCB: • • Disconnects or Stabs • Main disconnects — connect the circuit breaker to the main bus. • Secondary disconnects — connect the circuit breaker to the control circuits. • Ground disconnect — connects the circuit breaker to the ground bus.