A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of fire. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
Circuit breakers are made in varying sizes, from small devices that protect low-current circuits or individual household appliances, to large switchgear designed to protect high voltage circuits feeding an entire city. The generic function of a circuit breaker, or fuse, as an automatic means of removing power from a faulty system, is often abbreviated as OCPD (Over Current Protection Device). Also, there are many different types of Smart Circuit Breaker, Ewelink WIFI Circuit Breaker, Tuya WIFI Circuit Breaker, RS485 Circuit Breaker, Remote Control Circuit Breaker, Zigbee Circuit Breaker, Solar Systems Circuit Breaker, Automatic Recloser Circuit Breaker, DC WIFI Circuit Breaker, RS485 DC Circuit Breaker, etc.
Differences amoung overcurrents, overloads and short circuits
NEC defines and overcurrent as any current in excess of the rated current of equipment of the ampacity of a conductor. An over current is the result of an overload, short circuit, arc or ground fault. Effects of overcurrent include fires, conductor insulation damage and equipment damage.
According to NEC, an overload is the operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time would cause damage or dangerous overheating. An overload is NOT a short circuit, ground or arc fault.
A short circuit is an overcurrent which greatly exceeds the normal full load current of the circuit. Also, as the name infers, a short circuit leaves the normal current carrying path of the circuit and takes a short-cut around the load and back to the power source. A short circuit is an overcurrent but not an overload.
Circuit breaker components
Although low and medium voltage circuit breakers have unique designs that are specific to amperage, voltage and application, there are five main components that are universal across the different types of circuit breakers. The five universal circuit breaker components are:
Frame – Protects internal parts of the circuit breaker from outside materials
Operating mechanism – Provides a means of opening and closing the circuit breaker
Contacts – Allows the current to flow through the circuit breaker when closed.
Arc extinguisher – Extinguishes an arc when the circuit breaker interrupts a fault.
Trip unit – Opens the operating mechanism in the event of a prolonged overload or short circuit.