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Three-Phase Electrical Wiring installation in a Multi-Story Building

 Three-Phase Electrical Wiring installation in a Multi-Story Building

Multistory building Distribution System
  • Three Phase Energy meter 1 No
  • Three Pole MCCB, 100A, 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
  • Cupper strips for MCB Common connection, 3 Nos
Step by Step Procedure
To do Electric distribution system in a multi-storey building, follow the following steps.
As we have leaned the basic electrical wiring of bulb, fans etc (i.e. Sub-circuits and final sub circuits) so,
  1. 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 method How To Wire a 3-Phase kWh meter from the Supply to The Main Distribution Board?)
  2. Connect the MCCB (Moulded Case circuit Breaker) as three pole main switch to the incoming three phases (R, Y, B) from 3-phase energy meter
  3. Now connect the outgoing phases (R, Y, B) from MCCB (Moulded Case circuit Breaker) to the DP (Double Pole MCB , RCD, SP (Single Pole MCBs and load) of each storey, as shown in fig)
  4. Also connect the Neutral wires to RCDs and then to neutral links and then to specific loads (as shown in fig).
  5. Do not forget about earthling. So connect all loads with Earth link and earth link must be connected to the earth electrode viva earth lead (as shown in fig)
  6. Use the main breaker with proper rating i.e. which carry the total load current of all distribution boards of each storey but install the breaker in Sub distribution board according to that desired storey i.e. fans, lights etc in one storey and so on for other storey.
Click image to enlarge

 Multistory building Distribution System
Good to Know
In a Three Phase Wiring Distribution System;
Line to Line Voltage = 440V
Line to Neutral Voltage = 230V
L1 to L2 = 440V
L2 to L3 = 440V
L3 to L1 = 440 V
L1 to N = 230V
L2 to N = 230V
L3 to N = 230 V
In USA and other Countries…
L1 to L2 = 208V
L2 to L3 = 208V
L3 to L1 = 208 V
L1 to N = 120V
L2 to N = 120V
L3 to N = 120 V
Distribute Electrical wiring of each storey in three or four circuits. The purpose of this,
  • If a circuit breakerof a circuit or distribution board trip due to some reason, then all bulb and loads would not disconnect at once.
  • In case of one circuit instead of three circuits, if the load of storey increases, then more current will flow and cables may overheat. Also voltage drop would be increased. So rated voltage may not reach to electrical appliances,therefore, the light of bulbs would be dimmed. Moreover, due to overheat in the cables, there is also a risk of fire in the building.
General Precaution
  • Disconnect the power source before servicing, repairing or installing electrical equipments and installation.
  • Also use 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 to deal with electricity
  • Read all instruction and cautions and follow them strictly.
  • The author will not be liable for any losses, injuries, or damages from the display or use of this information or try any circuit in wrong format so please! Be careful because it’s all about electricity and electricity is too dangerous

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    1. thanksssss for this information.keep it up

    2. can we get 400V supply by using two phases while those two phases are also taken for 230V supply. Thank you

    3. from my analysis i can see the 1st storey is supplied by the red line the 2nd storey being the yellow phase and finally the 3rd being the blue line for instance if i have more than 3 storey which can add up to about 10 or more how would i manage to power the other storey..please illustrate to me with a diagram if its possible
      thank you

    4. how to calculate of power of a particular phase in a three phase system…

      each phase separately…
      can we consider 440v in each phase…
      like..P=VI cos

    5. Dear Engineer Waseem
      what sofware you are using for mcb electrical designe and drawing?

    6. mohammad rizwan alam

      dear sir
      how we will select breaker rating and cable size as per as load.
      if there is any formula pls illustrate me and reply.

    7. dear sir
      if the load of each floor is not same .and building is more than 3 storey. then how we do wiring

    8. send me the cost of lighting and heating circuits of multi storey say 5 floor…

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