AIR CIRCUIT BREAKERS - Electrical and Electronics Division

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MOULDED CASE CIRCUIT BREAKERS
L&T was the first company to introduce “Moulded case circuit Breakers (MCCBs)” in India. Over the years, it has developed &
enhanced the products to growing requirements of market conditions.
L&T MCCBs use latest technologies for circuit interruption under faults. These MCCBs comply with standards IS 13947, IEC 60947
and EN 60947-2 and are certified at independent and approved test authorities.
L&T offers a wide range of MCCBs with current ratings from 0.63A to 1600A in 3-Pole & 4-Pole versions & breaking capacity from
6kA to 100kA. These MCCBs are available with Thermal-Magnetic as well as with Electronic release (above 125A in DX range).
These MCCBs are available in �ixed or Drawout versions. They are also available in utilisation category ‘A’ or ‘B’.
L&T MCCBs are complemented with a wide variety of internal and external accessories.
APPLICATIONS
Distribution �eeders Ideally suited for incoming and outgoing feeder circuits on distribution boards.
Transformers Provide effective protection to distribution transformers as outgoing breakers on the LT side.
DG Sets Used for protection and control of diesel generating sets against overloads and short circuits.
AP�C Systems Suitable for controlling LT capacitors for power factor corrections.
DC Loads Suitable for both AC as well as DC applications. Hence find application in protecting rectifier panels.
UPS Used for UPS & Electronic equipment protection.
Motors Specially designed MCCBs for Motor back-up protection provide Type-2 co-ordination (as per IEC 60947)
in conjunction with suitably rated contactors and relays.
�urnaces Suitable for high frequency systems upto 400Hz and can be used for control of high frequency furnaces.
Also used in induction furnaces along with semiconductor fuses.
WORKING PRINCIPLE
L&T’s new range of MCCBs operate on “Current limiting” principle. This
helps in very fast clearance (less than 10 mS) of short-circuit faults. This is
achieved by –
1. Quick opening of main contacts.
2. Guiding the arc rapidly away from the contacts into the arcing chamber.
3. Quick quenching of arc by using effective arc quenching devices.
As a result peak short circuit current (I p ) is limited to cut-off current (I c ).
Thus, I2t let through (proportional to the shaded area) is considerably
reduced, resulting in lower thermal stresses in downstream equipments
and connecting cables.