Classification of Electrical Services

Alternating current electric power distribution systems can be classified by the following properties:

  • Frequency: 50 Hz or 60 Hz
  • Number of phases: single or three phase
  • Number of wires: 2, 3, or 4 (not counting the safety ground)
  • Neutral present:
    • Wye connected systems have a neutral
    • Delta connected systems typically do not have a neutral
  • Voltage classes: (ANSI C84.1-2016)
    • Low Voltage: 1000 volts or less
    • Medium Voltage: greater than 1000 volts and less than 100 kV
    • High Voltage: greater than 100 kV and equal to or less than 230 kV
    • Extra-High Voltage: greater than 230 kV but less than 1000 kV
    • Ultra-High Voltage: equal to or greater than 1000 kV

 

Wye Line-to-Neutral VoltageWye or Delta Line-to-Line Voltage
120208
1201240
230400
240415
277480
347600
  • Line-to-line voltages in three phase systems are typically 1.732 times the phase-to-neutral voltages: sqrt{3}=1.732
  • In symmetrical three-phase electrical system, the phase-to-neutral voltages should be equal if the load is balanced.
  • Note: 1201 Refers to a three phase four wire delta service.

 

Common Electrical Services & Loads

  • In the following drawings, the coil symbols represent the secondary winding of a utility service transformer or other step down transformer. Electrical code regulations in most jurisdictions require that the neutral conductor be bonded (connected) to the earth safety ground at the electrical service entrance.

 

Single Phase Three Wire

Single Phase Three Wire Electrical Service

Also known as an Edison system, split-phase or center-tapped neutral. This is the most common residential service in North America. Line 1 to neutral and Line 2 to neutral are used to power 120 volt lighting and plug loads. Line 1 to Line 2 is used to power 240 volt single phase loads such as a water heater, electric range, or air conditioner.

Three Phase Four Wire Wye

Three Phase Four Wire Wye Electrical Service

The most common commercial building electric service in North America is 120/208 volt wye, which is used to power 120 volt plug loads, lighting, and smaller HVAC systems. In larger facilities the voltage is 277/480 volt and used to power single phase 277 volt lighting and larger HVAC loads. In western Canada 347/600V is common.

Three Phase Three Wire Delta

Three Phase Three Wire Delta Electrical Service

Used primarily in industrial facilities to provide power for three-phase motor loads, and in utility power distribution applications. Nominal service voltages of 240, 400, 480, 600, and higher are typical.