3 Phase Distribution Board Layout and Wiring Diagram / Three phase DB Wiring with New Color Code

 I try to explain three phase distribution board layout and wiring diagram. Three phase power supply is required, when the Power distribution requirement cannot be handled by a single phase power supply.

Three-phase system can be described as the common method of alternating current power generation, transmission, and distribution. In this system, the current will pass through the three wires, and there will be one neutral wire for passing the fault current to the earth.

Updated Electrical Wiring Color Codes

Phase 1- Brown

Phase 2 - Black

Phase 3 - Gray


Protective Earth - Green-and-Yellow

How to Wire a Three Phase, 400V Distribution Board?

Three Phase Distribution Board

A distribution board is the combination of protective devices such as Main switch, MCB, MCCB, RCD, RCBO, Isolator, Fuses and Switches etc. used to control and safely distribute the power supply to the electric appliances and appliances.

A distribution board is also known as main breaker box, electric panel or panel board used in commercial (as industrial) and domestic (as residential) applications to fulfill the need for safe electrical installations and distribution.

In UK, EU and other countries following the IEC rules, the voltage between three phases (L1, L2, and L3) is 400V, Three Phase (4 or 5 Wires) while the voltage between any Phase and Neutral is 230V AC (2 and mostly three Wires including the protective earth "E"). This way, a three phase distribution can also provide single phase supply from any phase and neutral.

We already know the difference between single phase and three phase power supply as well as balanced and unbalanced loads system, so we will never repeat them again. Please note that we have only three phase MCB and load points in this panelboard as we have already discussed the single phase, split load, dual split load and combination of single phase and three phase distribution board and consumer unit wiring tutorials. Now let's move to the wiring installation of only three phase loads and distribution board.

How to Wire a Three-Phase Distribution Board?

As shown in the fig, the three phase, 400V (Three Lines + Neutral) service cable (from the secondary of Star or Y connected transformer (fed up by the secondary of delta connected power transformer) mounted on the utility (pole having 11kV voltage ) and 3-phase kWh energy meter) enters to the main distribution board.

All the three Lines (Phases) are connected to the three or four pole main switch MCB (Miniature Circuit Breaker) or MCCB (Molded Case Circuit Breaker). In case of 4 poles MCB/MCCB, the neutral should be connected to the neutral terminal mentioned on the breaker otherwise, connect the neutral directly to the neutral busbar terminal in the panel.

For enhanced and integrated protection, you may connect four RCD/RCCB poles right after the main switch. You may do the same for split load or dual split load distribution boards to transfer and separate the load points which depend only on a single RCD. We will discuss this scenario in our next post for 3-phase split load distribution board wiring installation.

All the 12 No. of three poles MCB's are connected to each live busbar i.e. Phase 1 or Line 1 as brown, Phase 2 or Line 3 as Black, Phase 3 or Line 3 as Gray. Keep in mind that Earth/Ground is must while Neutral is optional and depends on the system design especially in three phase load distribution.

400V Distribution Board Wiring - Old UK Wiring Color Codes

Some of the readers requested in the page inbox as well as email to include the Old UK wiring color codes (UK now using IEC wiring color codes) for three phase and single phase distribution boards and consumer unit as the same wiring codes are still applicable in many countries including India, Pakistan, United Arab Emirates, Saudi Arabia etc. So, here is the three phase distribution wiring according to old United Kingdom Wiring color codes (prior-2004).

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