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MCB and RCCB in Circuit

Normally RCCB is employed as the In-comer and MCB as outgoing feeders. Before RCCB was introduced, Isolator was engaged as Incomer and MCBs as feeders.

When RCCB initially came into vogue, both Isolator and RCCB started being used on the Incomer side. The Isolator acted as the main Incomer, immediately followed by RCCB. So on the Incomer side, the current 1st flows thru Isolator and then RCCB.

RCCB is a key ingredient in the electrical distribution system employed in homes and buildings as it protects individuals from being electrocuted. If the current leaks from electrical equipment the person coming in contact can get fatally electrocuted. RCCB protects us from such an unfortunate eventuality.

Forward-looking state Governments have made use of RCCB compulsory in homes. For domestic circuits, care must be taken to employ a 30 mA RCCB. All these MCBs, Isolator & RCCB are housed in the MCB-Distribution box. On the outgoing side (4way, 6way, 8way, 12way MCB-Distribution box) MCBs acted as the feeders to the various circuits.

With RCCB becoming popular, Isolator has been dispensed with and RCCB is solely used as Incomer.

Further explanation on the use of 2P and 4P RCCB.

  • In the SPN distribution board, 2P RCCB is used as In-comer and SP MCBs as outgoing feeders.
  • In TPN DB, 4P RCCB is used as In-comer and 3 separate Outgoing SP MCB ways (4, 6, 8, or 12 ways) are used for each of the phases.
  • In some states, for 3P circuits, (7 segment MCB-DB is mandatory)
    1. 1st segment at the top is the main 4P Isolator. Just below,
    2. 2nd line forms 3 segments. (2nd, 3rd,4th segment) In each segment, for each phase 2P, RCCB is used. So 3 nos. of 2P, RCCB is required.
    3. Below this is the 3rd line, forming 3 more segments (5th,6th, 7th segment)

These are the no. of ways, like 4, 6, 8, or 12way outgoing feeders, where SP MCBs are installed.

A 30 mA RCCB is strongly recommended for use in domestic installations. Walking barefoot within our homes, coming in direct contact with a faulty electrical gadget can get us electrocuted. Leakage current in excess of 30 mA can prove fatal. RCCB trips the circuit when leakage exceeds this threshold value.
For offices and other locations, and RCCB of 100 mA is used as the person using an electrical gadget is unlikely to be on bare feet. Meaning, contact with electrical gadgets could be termed as indirect. So a higher threshold is acceptable.

BCH Electric offers a wide range of high-quality MCB, RCCB, and MCB-Distribution boxes to customers across India.

KP Abbas, NSM, BCH Electric
(Note: BCH Electric Limited has no obligation for the data & information presented in this article, this information are the author’s independent knowledge & view)