circuit breakers

Miniature circuit breaker (MCB)

MCB is a mechanical switching device which is capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and automatically breaking currents under specified abnormal circuit conditions such as those of short circuit.

MCB characteristics

Rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation.

Description of MCB

1) Actuator piker ( for trip and reset )2) Actuator Device mechanism3) Main contact ( flow of current )4) Terminal Block5) Bimetallic steel strip6) Tripping calibration screw7) Solenoid coil8) Arc extinguisher - See more at:

How many pole for Miniature

1) One (1) pole For single phase use ( Live ) 2) Two (2) pole For single phase use ( Live & Neutral ) 3) Three (3) pole For three phase use ( R,S,T ) or TP ( three pole ) 4) Four (4) pole For three phase use ( R,S,T,Neutral) or TPN ( three pole &

neutral )

Current rating and short circuit current

Under fault conditions (such as a short circuit) much more current flows through the circuit than what it was designed for. A circuit that was designed for a maximum of 20A may suddenly be drawing hundreds, if not thousands of amps. The circuit breaker will trip if this occurs.

The value of the kA rating determines how much current the circuit breaker can withstand under fault conditions. The circuit breaker only has to withstand this for a brief period of time, usually the time it takes for the circuit breaker to trip. For example, a value of 6kA means that the circuit breaker can withstand 6,000 amps of current during the brief time it takes to trip.

MCB Selection

The first characteristic is the overload which is intended to

prevent the accidental overloading of the cable in a no fault

situation. The speed of the MCB tripping will vary with the

degree of the overload. This is usually achieved by the use of a

thermal device in the MCB.

MCB Selection

The second characteristic is the magnetic fault protection,

which is intended to operate when the fault reaches a

predetermined level and to trip the MCB within one tenth of

a second. The level of this magnetic trip gives the MCB its

type characteristic as follows:

MCB Selection

The third characteristic is the short circuit protection, which

is intended to protect against heavy faults maybe in thousands

of amps caused by short circuit faults.

The capability of the MCB to operate under these conditions

gives its short circuit rating in Kilo amps (KA). In general for

consumer units a 6KA fault level is adequate whereas for

industrial boards 10KA fault capabilities or above may be

required.

MCB advantages over fuse1-MCB is more sensitive to current than fuse. It detects any

abnormality in the current flow and automatically switches

off the electrical circuit.

2-In case of MCB, the faulty zone of electrical circuit can be

easily identified. Faulty circuit trips to the off position. On the

other hand in case of fuse, the complete fuse wire needs to be

checked by opening fuse grip for confirming the faulty zone

MCB advantages over fuse

3-With MCB it is very simple to resume to the supply. You just

need to push the knob of MCB back to on position. But in case

of fuse, the entire fuse wire needs to be replaced.

4-MCB provides a better interface with the help of knob than a

fuse. In case of fuse the compete handle needs to be taken care

out.

MCB advantages over fuse

5-Handling MCB is electrically safer than handling a

fuse.

6-MCB is reusable and hence has less maintenance and

replacement cost. Whereas a fuse needs to be replaced

whenever it goes faulty

Disadvantages of MCB

Only one disadvantage of MCB over fuse is that this system is more costlier than fuse unit system.

MCCB (Molded Case Circuit Breaker)

Characteristics Rated current up to 1000 A. Trip current may be adjustable. Thermal or thermal-magnetic

operation.

RCD (Residual Current Device / RCCB(Residual Current Circuit Breaker)

Phase (line) and Neutral both wires

connected through RCD. It trips the circuit

when there is earth fault current.

The amount of current flows through the

phase (line) should return through neutral .

It detects by RCD. any mismatch between

two currents flowing through phase and

neutral detect

RCD

by -RCD and trip the circuit within 30Miliseconed.If a house has an earth system connected to an earth rod and not the main incoming cable, then it must have all circuits protected by an RCDRCDs are an extremely effective form of shock protection. The most widely used are 30 mA (milliamp) and 100 mA devices.

RCD•RCD will not protect against a socket outlet being wired

with its live and neutral terminals.

•RCD will not protect against the overheating

•RCD will not protect against live-neutral shocks

Thank you.