Page 126 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

In MCCB, thermal and magnetic releases are adjustable. A shunt release is also incorporated for remote tripping
and interlocking at MCCB. MCCBs are provided with under voltages release. There are two types of MCCB.
1 Thermal magnetic type.

2 Fully magnetic type (Fig 2).
Advantages of MCCB
1 MCCBs occupy much less space in comparison to fuse switch units.
2 MCCBs provide equal amount of protection against high faults as switch gears having HRC fuses.
Disadvantages

1 MCCBs are much costlier.
2 Leak proof situation required.
3 Sensitivity to insulation resistance low.

Fig 1 & 2

ELCB - types - working principle - specification

Objectives: At the end of this lesson you shall be able to:
• explain the working principle, different types and construction of an earth leakage circuit breaker (ELCB)
• explain the technical specifications of ELCB’s.

Introduction
The sensation of electric shock is caused by the flow of electric current through the human body to earth. When
a person comes in contact with electrically live objects like water heaters, washing machines electric iron etc., the
extent of damages caused by this current depends on its magnitude and duration.
This kind of current is called the leakage current which comes in milli-amps. These leakage current being very
small in magnitude, hence undetected by the fuses/MCBs are the major cause for the fires due to electricity.

The leakage current to earth also results in the wastage of energy and excessive billing for electricity not actually
used.
These residual current circuit breakers (RCCB) are popularly called as Earth leakage circuit breakers (ELCB).
Basically ELCBs are of two types namely voltage operated ELCBs and the current operated ELCBs.

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CITS : Power - Electrician & Wireman - Lesson 20-25 CITS : Power - Electrician & Wireman - Lesson 20-25