Three(3) Phase to Single Phase Distribution Board Wiring Diagram

Termination of distribution board for beginners step by step guide for DB installation for industry and domestic use

Devices used in the DB
RCBO(Residual Current Breaker with Overcurrent)

Modern Distribution Boards use RCBOs instead of using the combination of MCB and RCCB because it provides the facilities of both MCB and RCCB. In the three-phase to single-phase distribution board, the four poles RCBO is used where all the three phases and neutrals go through the RCBO.

MCB(Miniature Circuit Breaker)

Generally, single-pole MCBs are used for the output loads. All three phases have an equal number of MCBs. For example, if the DB has eight MCBs, then each of all three phases will be connected to eight MCBs. So, the total MCBs in the box will be twenty-four (24).

Neutral Link

A neutral link is used to distribute a neutral supply to all the output loads. When single-pole MCBs are used for output loads, the neutral wire of the loads is connected to the neutral link.


Earth Link

The earthing terminal of the power supply and loads are connected to the earth link. Sometimes, the wire from the earthing pit is also directly connected to the earth link. Even the metallic body of the distribution panel is also connected to the earth link.


Connection Procedure
First of all, select MCB and RCBO Rating as per your load requirements.
Identify the input-output sides of the MCB and RCBO.
Also, identify the line and neutral terminals on the RCBO if it has.
Now connect all the there phases and neutral from the input power supply to the input of the RCBO.
Connect the L1(or R phase) terminal from the output of the RCBO to all the single pole MCBs that you want to connect with the L1 terminal or R phase.
Connect the L2(or Y phase) terminal from the output of the RCBO to all the single pole MCBs that you want to connect with the L2 terminal or Y phase.
Connect the L3(or B phase) terminal from the output of the RCBO to all the single pole MCBs that you want to connect with the L3 terminal or B phase.
Connect the neutral wire from the output of the RCBO to the neutral link. If the DB has multiple neutral links, then interconnect them with each other.
Connect the Earth Wire (it may come from the input power cable or earth pit) to the Earth link. If the DB has multiple Earth links, then interconnect them with each other.

Follow the below procedure if you use MCB and RCCB instead of RCBO,
Connect all three phases and neutral from the input power supply to the input of a 4-pole MCB.
Now connect the output of the 4-pole MCB to the input of a 4-pole RCCB.
Connect the neutral from the output of the RCCB to the neutral link.
Connect all three phases from the output of the RCCB to the single-phase MCBs by connecting an equal number of MCBs per phase.
Earthing connection is the same for both types of connection.