Circuit Breaker Design and Components

Almost all circuit breakers have five basic components:

1. External Casing : This is the external shell that encases the other parts. Based on the rated current and voltage, they are further divided into three types:

Molded Case: Typically used in low voltage circuit breakers

Insulated Case: Used in circuit breakers rated for medium voltage and amperage

Metal Clad: Generally for the higher end of the medium-rated circuit breakers

2. Electrical Contacts : There are two contacts in a circuit breaker – a fixed contact and a floating contact (which is controlled by the circuit breaker). When the breaker trips, the floating contact moves away from the fixed contact and disconnects the electricity supply into the circuit.

3. Electrical Arc Extinguishing Mechanism : When the contacts disconnect, electricity can jump through the gap between the last parts in contact. This creates an arc of electricity that can reach very high temperatures. To prevent damage and keep the arc from recreating itself, a circuit breaker uses an arc quenching mechanism to stop these arcs.

4. Main Operating Mechanisms : Circuit breakers can use a variety of methods to disconnect power supply. These can include spring-loaded switches, solenoids, hydraulic and pneumatic switches.

5. Trip Elements : Current flowing through a circuit creates heat and a magnetic field. Trip elements are calibrated to use either or both these factors to gauge the current and voltage and trip a switch, in case the maximum ratings are exceeded.

Types of Circuit Breakers

There are many types of circuit breaker designs and they can be classified on the basis of voltage (high, medium and low) or other characteristics like their arc quenching media and operating mechanism: