Beginners' design course:Electrical System Configurations

Typical Electrical System Configurations :
  • 2-Wire, Single Phase (Outside U.S.).
  • 3-Wire Single-Phase.
  • 3-Wire 3-Phase Delta (Corner Ground).
  • 4-Wire 3-Phase "Wye".
  • 4-Wire, 3-Phase Delta (High Leg).
2-Wire, Single-Phase System see fig.1
this system is applied Outside of the United States, a variety of voltages used in this system configuration according to the standard applied in each country.
This system is different from the US "Edison System" in that only one voltage is available 



Single Phase 240V (see fig.2)

3-Wire, Single-Phase System see fig.3
The 3-wire, single-phase Edison system is the only approved method of wiring single­phase systems in the United has two voltages available one 120V and the second is 240V.

Single Phase 120/240V (see fig.4)


3-Wire, Three-Phase Delta System (Corner Ground) see fig.5This system configuration is the simplest one , it normally used in the transmission of intermediate voltages from 15,000V to 600V where the neutral conductor is not used. It is also used in industrial facilities by grounding one "corner" of the System. 
The corner-grounded Delta system minimize the wiring costs, and the grounded phase can be used to physically protect the other two phases from accidental grounding or lightning strikes in outdoor settings. 
The disadvantage of this system is inability for distributing power to single phase loads. 

  • 220 Volt Corner Ground (see fig.6)
  • 440 Volt Corner Ground (see fig.7)


4-Wire, Three-Phase "Wye" System see fig.8it is the most common electrical system configuration, the ground voltage or voltage available from phase to ground is the phase voltage divided by 1.73
As with all other grounded systems, bonds are established between the grounded neutral and all components of the system. This system is recognized as the safest possible multi-purpose distribution system for low voltage (in the United States). Outside the United States, common voltages are 215v/380, 220v/400v, and 230v/415v. 

in the united states: 
  • 3-Phase 120/208 Wye (see fig.9)
  • 3-Phase 277/480 Wye (see fig.10)


outside the united states:

  • 3-Phase 220/380 Wye (see fig.11)
  • 3-Phase 220/400 Wye (see fig.12)
  • 3-Phase 230/415 Wye (see fig.13)
  • 3-Phase 347/600 Wye (see fig.14)




4-Wire, Three-Phase Delta System see fig.15
the using of this electrical system configuration is restricted by the following precautions:

1- all loads must be carefully balanced on both the single-phase and three-phase legs.
2- high leg must be color identified  " usually orange" to avoid using it as a single phase source  
because the voltage between one leg and the grounded neutral is considerably higher than the rest of the single-phase system, high leg  is located between the two lower voltage conductors. 
3- don't use the "high leg"  as a single-phase source because no ground or grounded neutral exists for this circuit. 

3-Phase 120/240 Delta (Hi-Leg )(see fig.16)

in the next Topic, I will explain the Electrical system voltage classes and the SI Units system. please, keep flowing.

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