Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
The circuit breaker which does not contain any serviceable part is known as:
Oil circuit breaker (OCB)
Miniature circuit breaker (MCB)
Air circuit breaker (ACB)
Air blast circuit breaker (ABCB)
Miniature circuit breaker (MCB)
A Miniature Circuit Breaker (MCB) is a hermetically sealed, compact electromagnetic device designed for low-voltage residential and commercial circuits. Because it is factory-sealed to ensure calibration and safety, it contains no field-serviceable parts; once it fails or trips beyond its mechanical life, it is replaced as a complete unit.
A Miniature Circuit Breaker (MCB) is a hermetically sealed, compact electromagnetic device designed for low-voltage residential and commercial circuits. Because it is factory-sealed to ensure calibration and safety, it contains no field-serviceable parts; once it fails or trips beyond its mechanical life, it is replaced as a complete unit.
TтИЭI21тАЛ тАФ Relationship between tripping time and current in inverse time characteristics
F=BIl тАФ Magnetic force acting on the solenoid plunger during short circuit
The MCB operates on two main mechanisms: a bimetallic strip for inverse time-current characteristics (thermal protection against overload) and an electromagnetic solenoid for instantaneous tripping (short-circuit protection). When a fault occurs, the mechanism triggers a spring-loaded toggle, opening the contacts and extinguishing the arc within a built-in arc chute.
MCBs provide both thermal and magnetic protection in a single integrated unit.
The sealed construction prevents dust and moisture ingress, maintaining calibration.
Designed for current ratings typically up to 100A and low voltage (usually < 1000V).
Does not require routine maintenance, making it cost-effective for small-scale installations.
Compact size and easy installation
High operational safety due to sealed casing
Reusable after manual resetting
Accurate and consistent tripping characteristics
Cannot be repaired if internal components fail
Limited capacity compared to industrial Air Circuit Breakers (ACB)
Susceptible to wear if subjected to frequent heavy-fault interruptions
Residential wiring and distribution boards
Small-scale industrial motor protection
Office building lighting and power distribution
Serviceable circuit breakers like OCBs or ACBs allow contact replacement or oil filtering.
MCB usage is governed by IS/IEC 60898 standards.
B is correct тАФ The MCB is a factory-sealed, maintenance-free device intended for direct replacement rather than repair of individual components.
Always remember that 'serviceable' is a key differentiator in switchgear; high-capacity breakers (ACB/VCB) are designed for maintenance, while low-capacity breakers (MCB/MCCB) prioritize affordability and simplicity.