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MCB and RCCB in Circuit

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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 Incomer side. The Isolator acted as main Incomer, immediately followed by RCCB. So in the Incomer side, 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 current leaks from an 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 use of 2P and 4P RCCB.

  • In 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 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 bare foot 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, RCCB of 100 mA is used as the person using 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 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, these information are author’s independent knowledge & view)