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Three Phase Electrical Wiring Installation in Home – NEC & IEC

3-Phase & 1-Phase Electrical Distribution Wiring Installation in Home

In our today electrical wiring installation tutorial, we will show how to do a Three Phase Consumer Unit Installation from Utility Pole to a 3-Phase Energy Meter & 3-Phase Distribution board and then How to connect Single Phase & Three Phase Loads in a Three Phase Wiring Distribution System in home electric supply system.

Related Wiring Tutorials:

What is Three Phase & Single Phase Power?

In power generation plants, Three Phase power is generator by electrical generator or alternator. In an alternator, the generated voltage and current by three independent coils in stator are apart by 120 degree from each other. The generated power from alternators then transmitted and distributed through transmission and distribution lines to the sub distribution.

In industrial and commercial buildings, they need high power. So they are connected to the three phase Delta connection(3 Phase – 3 Wire System – No Neutral Wire) before distribution transformer and then manage the required voltage and current according to their needs in three phase and single phase supply.

On the other hands, buildings that need high power in three phase and single phase, they are connected to the secondary of distribution transformer. This way, they get three phase Star connection (3-Phase, 4 Wire System with Neutral Wire). In the Star connection, Three Phase Line to Line (Phase to Phase) voltage are 415V AC (in US, 208V) and Single Phase Line to Neutral (Phase to Neutral), there are 230V AC (120V in US)

In Three Phase Supply, motors and large electric heaters can be directly connected to the Three Phases while in in Single Phase, load (Light, fan etc) can be connected in between Phase and Neutral through proper protective devices.

Why We Need Three Phase Power Supply?

To operate high power equipment and appliances such as electric motors and and high power rated air compressor etc, we need Three Phase Power supply instead of Single Phase Power supply. In ordinary homes, we mostly use Single Phase power supply to operate lighting load, fans, washing machines etc, but in some cases as well as industries offices high torque motors, multi-storey & large buildings, Three Phase power supply needs to operate and maintain the system.

In our previous posts, We did it for Single Phase electrical wiring installation in home and already know that what are MDB, DB, Final Sub Circuit, MCB, MCCB, CB and RCD etc.

Requirements for Three Phase Wring Installation

In this tutorial, we need the following wiring accessories to wire three phase power in home.

  • Three Phase Energy meter 1 No
  • Three Pole MCCB, 63A, 1 No
  • Double Pole, 63A, 30mA Trip Current RCD, 3 Nos
  • Double Pole MCBs, 63A, 3 Nos
  • Single Pole, 20A, MCB, 6 Nos
  • Single Pole, 16A, MCB, 3 Nos
  • Single Pole, 10A, MCB, 6 Nos
  • Distribution board cases, 3 Nos
  • Bus bar Link for Neutral Cable Connections
  • Copper strips for MCB common connection, 3 Nos (Cu Busbar segment)
  • Copper strip Busbar for Earth & Ground Link

Related Post: Different Types of Electrical Wiring Systems and Methods of Electrical Wiring Installation

How to Wire There Phase Main Distribution Board?

Generally, Electric supply and service providers install a single phase energy meter when load is less than 7.5kW (10HP) in domestic areas (consumer unit for home). If the limit is exceeded, then it’s recommended to install a 3-phase energy meter for consumer units. when load is exceeds from 7.5 kW, then 3-phase electrical wiring is recommended in domestic areas (homes).

In this tutorial, We assume that we will only connect single phase load (Light points, fans, TV, Power Socket, AC etc.) in this three phase electrical wiring installation. In other words, we will not power up 3 phase motors because in our homes, we haven’t that kind of (three phase) loads. If three phase load exists in your home, then you can do so. As we can see that the total load is exceeded the limit of single phase electrical wiring installation as we will be feeding different rooms and areas in home, that’s why we have to wire our distribution in three phase system.

Practical Procedure of Three Phase wiring of distribution board & installation

We have learned the basic electrical wiring of bulb, fans etc (i.e. Sub-circuits and final sub circuits) in our previous posts, so follow the steps below to do the same as mention below..

  • First of all, connect the three-phase energy meter as shown in fig. ( if you don’t sure that how to wire a 3-phase energy meter, then check this simple tutorial which show How to wire a Three-Phase Energy Meter.
  • Connect the MCCB (Moulded Case circuit Breaker) as main switch to the incoming three phases (R, Y, B) from 3-phase energy meter. (Check the wiring color code for different areas in below section)
  • Now connect the outgoing three phases (R, Y, B) from MCCB (Moulded Case circuit Breaker) to the DP (Double Pole MCB , RCD, SP (Single Pole MCBs and load) as shown in fig)
  • Now connect the RCD from DP with Phase (Line) and Related Neutral Link. The Out going Phase lines should be connected to the final and final sub circuits. The same can be done for Neutral Wires.
  • Finally, Connect the electrical appliances with the Earth link terminal which leads to earth electrode in the earthing and grounding system as shown in fig below.
  • Do the the same steps for all three distribution boards for different rooms and areas.
 Click image to enlarge
Three Phase Electrical Wiring Installation Diagram
Fig 1 – Three Phase Electrical Wiring Installation Diagram

Good to Know

You may also use a Four Pole MCCB instead of Three Pole MCCB. Simply connect the Neutral wire in the last slot of that MCCB (Incoming and Outgoing like other phases) and then connect the outgoing Neutral to copper strip (i.e. Earth Link) as shown in fig.

Wiring Diagram of Three Phase Distribution Board

Click image to enlarge

Electrical Wiring Diagram of Three Phase & Single Phase Consumer Unit with RCD
Fig 2 – Electrical Wiring Diagram of Three Phase & Single Phase Consumer Unit with RCD

Wiring Color Codes of IEC and NEC

Wiring Color Code:

We have used Red for Live or Phase , Black for Neutral and Green for Earth Wire. You may use the specific area codes i.e. IEC – International Electrotechnical Commission (UK, EU etc) or NEC (National Electrical Code [US & Canada] where;


Single Phase 120V AC:

Black = Phase or Line, White = Neutral and Green/Yellow = Earth Conductor

Three Phase 208 AC:

Black = Phase 1 or Line1, Red = Line 2, Blue = Line 3, White / Gray = Neutral and Green/Yellow = Earth Conductor


Single Phase 230V AC:

Brown = Phase or Line, Blue = Neutral and Green = Earth Conductor

Three Phase 208 AC:

Grey= Phase 1 or Line1, Black = Line 2, Brown = Line 3, Blue = Neutral and Green = Earth Conductor

Below are given the Three Phase Distribution Electrical Wiring Installation Diagram according to NEC & IEC.

Three Phase Electrical Wiring Installation Diagram According to NEC Color Code

Click Image to enlarge

Three Phase Distribution Board Electrical Wiring Installation Diagram According to NEC Color Code
Fig 3 – Three Phase Distribution Wiring According to NEC Color Code

Three Phase Electrical Wiring Installation Diagram According to IEC Color Code

Click image to enlarge

Three Phase Distribution Board Electrical Wiring Installation Diagram According to IEC Color Code
Fig 4 – Three Phase Distribution Wiring According to IEC Color Code

Note: The same description and details can be for both NEC and IEC wiring diagrams used as mentioned for the above general fig 1.

How to Connect Single Phase & Three Phase Loads in a Three Phase Wiring Distribution System?

As mentioned above, Three Phase loads (415V or 208V AC Such as 3-Phase Motors) can be directly connected to the three lines accordingly i.e. there is no need to connect to the neutral point. For Single Phase Loads (230V or 120V AC Light, TV, Power socket, Fans etc), They can be connected to the Phase and Neutral wire as shown below. Note that Earth or ground wire must be connected to the electrical appliances and equipment connected to both single phase and three phase supply system for safety.

How to Connect Single Phase & Three Phase Loads in a Three Phase Wiring Distribution System?
Fig 5 – Single Phase & Three Phase Load Connected in Three Phase Supply System

Good to Know

In a Three Phase Wiring Distribution System (Star Connection i.e. 3 Phase, 4 Wire System);

Line to Line Voltage = 415V AC (208V in US)

Line to Neutral Voltage = 230V (120V in US)


  • L1 to L2= 440 V
  • L2 to L3= 440 V
  • L3 to L1= 440 V


  • L1 to N = 230 V
  • L2 to N = 230 V
  • L3 to N = 230 V

in USA and other Countries

  • L1 to L2= 208V
  • L2 to L3= 208V
  • L3 to L1= 208V


  • L1 to N = 120V
  • L2 to N = 120V
  • L3 to N = 120V

Related Post: How to Connect a Portable Generator to Home Supply System (Three Methods)

General Precautions

  • Electricity is Our Enemy, if you give it a chance to kill you, Remember, they will never miss it. Please read all caution and instruction while doing this tutorial in practical.
  • Disconnect the power source before servicing, repairing or installing electrical equipments.
  • Ue the proper cable in size with this simple calculation method ( How to determine the suitable size of cable for Electrical Wiring Installation)
  • Never try to work on electricity without proper guidance and care.
  • Work with electricity only in presence of those persons who has good knowledge and practical work and experience who know how to deal with electricity.
  • Read all the instruction and cautions and follow them strictly.
  • Doing your own electrical work is dangerous as well as illegal in some areas.Contact the licensed electrician or the power supply company before practicing any change in electrical wiring connection.
  • The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

 You may also check the related Electrical Wiring Installation Tutorials.

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Electrical Technology

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  2. saugata sen says:

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    1. Electrical Technology says:

      Thanks for your kind words…

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  17. In the diagram, no protection (switchgear) is used between utility pole and incoming of 3-ph energy meter…is direct connection from utility pole to meter OK or is it necessary to use any fuse/cut??

  18. Anand Singhal says:

    Thanks. The information is very useful since I am constructing my own 4 bedroom house in New Delhi. I have a query though: i would like to have one light; fan and TV in each room to be connected to a single phase UPS. The electrical contractor is asking for high extra payment for doing this. Would there be significant extra cost involved. I would have thought that the only extra is drawing one wire from the mains to the UPS and from the ups to the bus for emergency circuits. The wiring of the mergency circuits would not change since they would get power from the grid normally and from the ups in case of power failure

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  20. One ups power and multi utility meters wiring diagrams

  21. I want to 3,phase and single phase electrical panel energy meter CIRCUIT

  22. Abdul quadri Ismail adio says:

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  23. what cause circuit breaker to read 439v and trips most of the time

    1. Vijay prabhudas ingle says:

      2003 starting to helper working in metro Delhi

  24. Im really impressed from your work.

    Please can you guide or send me a link to understand a change over switch and a phase selector in a 3 phase environment.

  25. Consider a max 10 KW connection is provided by electricity board then what will be max power capacity at each phase?

    Total Power : 10 KW
    Electricity Board : MAHA VITARAN

    Phase 1(R) : V = ? & I = ?
    Phase 2(Y) : V = ? & I = ?
    Phase 3(B) : V = ? & I = ?

  26. we ask some question the building the install wiring is three phase but the wiring is single phase that building have a laboratory so i think some lab need 3 phase for the units so how to install 3 phase electrical wiring , the electric compony install 25 kva its that enough for the load of the building.

  27. gamal ateya says:

    I can not understand how Phase to Phase voltage is 440 volt , and phase to neutral voltage is 230 v ?
    as i know V phase to neutral = VLine/ root 3

    so for 440v VL , V phase = 254 volt ?

    please correct if I am wrong

    1. Electrical Technology says:

      You are ignoring the Power factor in 3 Phase system….

  28. 25hp motor can you use 220v contactor?

    1. Khizar Awan says:

      yes of course . you can use . but the conducting capicity should be higher than your running load .

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    Thanks so much

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  33. ssenabulya lawrence says:

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  34. nick strong says:

    how should i wire a three phase water heater to single phase 240 volt. i have two 120 legs and a neutral to attach to 3 lugs and a neutral in the heater.

  35. Olusola Ogunsina says:

    Please can you present a well illustrated diagram showing how a free standing 3-Phase AC is connected. I am intrested in the details at the switching point of the AC.


  36. simple methods of installing a hammer mill( electrical wiring)

  37. Engr. Igunbor Alexander Iyare says:

    Please give me a practical example on how to determine the DB load balancing for a three phase supply system for an architectural building design electrical drawing aspect.

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