Low Voltage ACB Earthing

Earthing terminal are provided on Cradle of ACB which is a made of Sheet steel & need earthing. On Breaker either ACB OR MCCB no earthing terminal is provided

MCCB is "Moulded Case Circuit Breaker" and it is used for Power Switching applications.
It is available in a variety of continuous current ratings from 16A to 3200A and also with
short circuit breaking capacities ranging from 10kA to 75kA. They are capable of Making,
Carrying & Breaking Electric Currents in Circuits during Normal Conditions as well as during
abnormal or faulty conditions. An MCCB normally will have over current & short circuit
protection. Nowadays, MCCBs are also available with in-built earh fault protection.

A MCCB has a housing that is made from non conductive material. Available for low voltage
applications and comes in amperages from the single poles in the panel in your house to
3 phase and about 4000A.

Earthing terminals are provided on the metallic body/enclosures/panels etc for safety of personnel by providing a path for any leakage current due to insulation failure in the concerned equipment.

These metallic parts are not supposed to carry any current under normal condition.Accordingly the metallic panels/enclosures housing ACB/MCCB/VCB are invariably provided with earthing terminals.But, earth terminals are never provided on the ACB/MCCB/VCB itself. You may note that in 4 pole ACB/MCCB Neutral terminal is also available in addition to the 3 phase terminals (But, no Earth terminal).

As regards functioning of the MCCB under earth fault condition, in-built current transformers will sense the fault & trip the MCCB if the earth fault protection release is provided therein.

Hope, this is clear.

The other name for MCCB is totally insulated circuit breaker. In an ACB, the enclosure or case is metallic anbd hence during an earth fault, the fault curent might find a path thro the case, which might develop dangerous touch voltage hazards for human beings. To provide an alternate low impedance path for the fault current, one provides earthing connection to the ACB case.

Wheras in an MCCB as the case is made up of insulating material, no current can flow thro the case and hence no earthing terminal is required.