MCB Flashcards
What is an MCB and what does it stand for?
Miniature circuit breaker.
It is a mechanical protection device capable of making, carrying and breaking currents under normal and abnormal circuit conditions.
What else can an MCB be used for?
It can be used as a switch for a particular circuit.
What are the two types of tripping mechanisms and explain?
Thermal tripping: Overload current passes through the MCB, which causes a bi-metallic strip to slowly bend over and open the breaker.
Magnetic tripping: When a short circuit occurs, the high current in the magnetic coil produces a strong magnetic field, which instantly opens the breaker.
How are the bi-metallic strip and magnetic coil connected in an MCB?
They are connected in series.
What is the thermal tripping factor for MCBs? What stays true?
It is a range from 1.13 - 1.45 multiplied by the MCB current rating. This is true for all MCB types.
What is the magnetic trip factor for each type of MCB?
Type B: (3-5) × rated current (In)
Type C: (5-10) × In
Type D: (10-20) × In
Describe each type of MCB.
Type B: Suited for domestic and commercial uses where little to no switching surges are likely.
Type C: Generally suited for commercial and industrial installations in use of small motors.
Type D: Should be used where there is an abnormally high rush in current when some device, like an X-ray equipment, is switched on.
List 3 advantages of MCB’s?
It is easy to identify when tripped, even when dark.
Does not normally require replacement.
Doesn’t age in service.
Gives accurate protection and is tamper proof.
