Methods of Circuit Wiring as per Bangladesh National Building Code.

The wiring recommendation as per BNBC and NFPA are simple and clear. A single circuit / branch circuit might have several same load or several multiple type of load looped connected and that circuit must be protected by a switchgear -mcb/mccb/fuse. The looping can not be done in the breaker input or output nor there will be multiple cable(multiple cable to separate branch circuit.). But multiple cable to a single branch circuit is valid. Say in a 800amp MCCB 5 nos of 120rm cable can be used but this all 5 cable should be connected the same circuit, if one of them is connected to another circuit that is not valid.

BNBC 2.5.2 Methods of Circuit Wiring

[adsfl]Branch Circuit:Separate branch circuits shall be provided for the installation which needs to be separately controlled. These branches should not be affected by the failure of other branch circuits.Separate branch circuits shall be provided from miniature circuit breaker (MCB) or fuse distribution boards (FDB) for general lighting, automatic and fixed appliances with a load of 500 watt or more and plug receptacles. Each automatic or fixed appliance shall be served by an individual circuit.

So, A single mcb/mccb will protect a single circuit, the circuit might have looped multiple loads, multiple types of loads but not socket and light in the same circuit. We have seen that the mcb/mccb is looped from input to skip installing bus bar. But this is not recommended by BNBC. Every single switchgear- mcb/mccb will feed from bus bar.

Switchgear capacity:Circuits with more than one outlet shall not be loaded in excess of 50% of their current carrying capacity. Individual branch circuits must have spare capacity to permit at ]least 20% increase in load before reaching the level of maximum continuous load current permitted for that circuit. At least one spare circuit must be allowed in the distribution board for each five circuits in use.

[alvaa]Separation:Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent unwanted energizing of a final circuit.

Distance to load: Size of wire to be used in a branch circuit shall be at least one size larger than that computed from the loading if the distance from the over current protective device to the first outlet is over 15 m. When the distance from the over current protective device to the first socket outlet on a receptacle circuit is over 30 m, the minimum size of wire used for a 15A branch circuit shall be 4 mm² (7/0.036). The length of lighting circuits shall be limited to a maximum of 30 m, unless the load on the circuit is so small that voltage drop between the over current protective device and any outlet is below 1%.

The use of common neutral for more than one circuit shall not be permitted.

Looping examples-

Looping mcb
Looping mcb
Looping mccb
Looping mccb

Bunch of cable examples-

Bunch of cable
Bunch of cable

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