MCCB (Moulded Case Circuit Breaker) – Short circuit and overload protection device, commonly used in the protection in low voltage power distribution and industrial applications. MCB (Miniature Circuit Breaker) – Short circuit and overload protection device, commonly used in the protection of household devices and devices with low short-circuit currents. It can be commonly seen in substations and are used to isolate transformers from the service during maintenance. Isolators and switch disconnectors are less often used in low voltage system. Switch disconnectors are also a type of isolator/ disconnector. They do not offer any kind of protection to the circuit or device. Isolators are offload devices, meaning the current flow through the isolator should be zero before the operation. Isolators or disconnector are devices used to isolate a circuit or equipment from the power supply during maintenance, in order to ensure the safety of workman. The short circuit breaking capacity of an RCBO varies up to 15kA. Also, continuous current ratings of 25A, 40A, 63A, 80A, 100A and 125A are available.
The leakage current sensing range of RCBO ranges as 10Ma, 30mA, 100mA and 300mA. RCBO is available in two poles and four-pole versions. where the risk of electric shock and overload are more.
It is used for the protection of devices like geysers, hairdryers etc. RCDs are stand-alone devices and do not require MCB backup as in the case of RCCB. It is designed to withstand short circuit currents and has arc chutes within. It constitutes short circuit, overload and residual current protection features. Residual current circuit breaker with overloadĪ residual current circuit breaker with overload (RCBO) is a combination of RCCB and MCB. It is available with a continuous current rating up to 2500A. MCCBs can have short-circuited current withstand capability up to 200kA (200,000A). MCCBs are mostly used in power distribution and protection of industrial equipment such as motor starters, drives, pumps etc. Thermomagnetic trip units use the bimetallic strip for current sensing and operation and microprocessor-based units consist of built-in CTs for current sensing and operate the circuit breaker in the event of a fault. It -may be thermal or microprocessor-based units. MCCBs are equipped with trip units to sense and interrupt the current flowing through it. Some of these breakers also have an inbuilt ground fault/ residual current protection features. Also, the continuous current rating of the same can be adjusted as per requirement. Moulded Case Circuit Breakers can withstand more short circuit current more than miniature circuit breakers. Similar to Miniature Circuit Breakers, Moulded Case Circuit Breakers are also overload and short circuit protection devices. MCBs are available in single, double, triple and four-pole versions and continuous current rating from 0.5A up to 100A. Miniature circuit breakers can be used for the protection of lamps, home appliances, electronic devices and equipment with low short-circuit currents. However, short-circuit breaking capacity of an MCB varies up to 15kA.
MCBs can safely act during short circuits resulting in the current flow up to 15kA, depending on its short circuit breaking capacity. MCBs are most commonly used in the distribution board at home. Higher the intensity of fault quicker shall be the MCB action. Miniature circuit breakers sense such excessive currents and disconnect the load from the source, thus preventing greater damages to the load. During overload and short circuits excessive current flows to the load that may damage the equipment. The miniature circuit breaker is a protection device that prevents damage to an equipment /circuit on the event of an overload or short circuit faults.