Q: State
difference between MCB & MCCB, Where it is used?
Ans: MCB (miniature circuit breaker) thermally
operated device and used for overload and short circuit protection in small current rating. Usually
it is used not more than 125A and factory set O/L and S/C setting.
MCCB (molded case circuit breaker) is thermal
operated for over load current and magnetic operation for instant trip at short
circuit condition.Thermal and Magnetic protections are adjustable.Under voltage and under frequency may be incorporated.Now a days microprocessor based protections are available.
Q: What is the
difference between Isolator and Circuit Breaker?
Ans: Isolator is a no-load device which is used to
isolate the downstream circuits from upstream circuits for maintenance purpose. Isolator cannot operate in fault conditions, actually they used for isolating the circuit breakers for maintenance.
It is manually operated and does not have any automatic trip mechanism like in
circuit breaker.
Whereas circuit breaker is on-load automatic device
used to make and break circuit in both normal and abnormal conditions like
short circuit, overload etc.
Q.What is
RCD/RCCB?
Ans: RCD/RCCB (Residual current device/Residual
current circuit breaker).
Phase and neutral connected through RCD. It trips
the circuit to be protected during earth fault. The amount of current flows
through phase should return to neutral. In case of earth fault there is
mismatch which is sensed by RCD and trips the circuit.
RCD/RCCB trips for leakage current of order 30mA, 100mA,
300mA .
Q: Why ELCB can't
work if N input of ELCB do not connect to ground?
Ans: ELCB is old name of RCCB.ELCB is used to
detect earth leakage fault. Phase and neutral of service line are connected to
ELCB.
The current will flow through phase and that much
current will have to return neutral so resultant current is zero. During ground
fault in the load side, current from phase will directly pass to earth, not
return through neutral of ELCB. That means there is mismatch of current and ELCB
will trip.
If the neutral is not grounded, fault current will return
back through ELCB so there will be no mismatch in current hence no tripping of
ELCB.
Q: What is Air
Circuit Breaker(ACB)? Where it is used?
Ans: In ACB air is used as arc quenching medium.
Rated current up to 400 to10000A. Thermal or
thermal-magnetic, under voltage, over voltage protections are available in ACB. This
type of CB is used up to 11 KV.
Q: What is MOCB? Where
it is used?
Ans: Minimum oil circuit breaker(MOCB) uses mineral oil
as arc quenching medium.
Usually used between 11- 66 KV. This type of CB is
available up to 8000MVA at 245 KV.
Q: What is Air Blast
Circuit Breaker? Where it is used?
Ans: In ABCB air blast is used as arc quenching
medium.This is of two types a)Axial blast b)Cross blast type.