Single Phase, Three Phase and AC Around the World

In the last lesson we learned about AC. Now we answer two simple questions. First: what is the difference between single phase and three phase? Second: is the AC supply the same in every country? (It is not.) At the end you can look up the rating in your own country. Every step has a simulator: drag the sliders and watch what changes.

+ WORDS USED ON THIS PAGE (OPEN THIS IF A WORD IS NEW)

phase line (L): A live wire that carries one AC voltage wave. Three phase has L1, L2 and L3.
neutral (N): The return line.
single phase: One phase line and one neutral line. Used in homes.
three phase: Three phase lines, each with its own wave. Used in industry for big motors.
phase difference: The gap in time between the moments the three lines reach their peak.
phase-to-phase voltage: The voltage measured between any two phase lines.
phase-to-neutral voltage: The voltage measured between any phase line and the neutral.
3 wires and 4 wires: 3 wires = L1, L2, L3 only (no neutral). 4 wires = L1, L2, L3 and N.
frequency (Hz): How many AC cycles happen in one second: 50 Hz or 60 Hz.

PART 1 Single phase, three phase and the ratings

Press Next to move through six steps. Back to return. The picture on the left stays in view while you work with the controls on the right.

PART 2 Questions beginners ask

Where is single phase used, and where is three phase used? Homes use single phase for lamps, sockets and small motors such as a household water pump. Industry uses three phase for big motors, large pumps and machines. These are the machines a PLC controls.

Is the neutral the same as the minus (−) in DC? Almost. It is the return wire. In AC the current goes out along the phase line, then comes back along the neutral, and then the direction flips, many times every second.

Some supplies have no neutral. How does the current return? In a 3-wire supply the three phases share the job: current that goes out along one comes back along the others. You do not need to work this out now. Just remember that a three-phase motor needs only L1, L2 and L3.

Why two voltage ratings? Because there are two ways to connect equipment. A three-phase motor is connected to the phases, so it uses the phase-to-phase voltage (like 380 V or 400 V). A lamp is connected between one phase and the neutral, so it uses the smaller phase-to-neutral voltage (like 220 V or 230 V). The motor nameplate tells you which one it needs.

PART 3 Single phase vs three phase

	Single phase	Three phase
Phase lines	1	3 (L1, L2, L3)
Neutral	1 neutral line	With or without (4-wire or 3-wire)
Voltage ratings	One	Two: phase-to-phase and phase-to-neutral
Used for	Homes: lamps, sockets, small motors	Industry: big motors and machines

Key idea. Three phase is a smoother form of power. Power stations generate three phase, and it is the choice for driving motors in industry.

Examples from the world list (industrial three phase):

Country	Voltage	Frequency	Wires
India, Germany, UK, France	400 V	50 Hz	4
Australia	400 V (often 415 V)	50 Hz	3, 4
Saudi Arabia	400 V	60 Hz	4
Brazil	220 V / 380 V	60 Hz	3, 4
USA	120/208 V, 277/480 V and others	60 Hz	3, 4
Canada	120/208 V, 240 V, 480 V, 347/600 V	60 Hz	3, 4

PART 4 Find the rating in your country

This list comes from the World Standards three-phase table (industrial use only, last updated 23 January 2024). Search for your country, then check whether your equipment matches. Always check before you start a design, because a mismatch can cause a serious problem.

CountryVoltageFrequencyWires

Your equipment voltage (V)

Frequency

How to read the Wires column: 3 means three phase without neutral. 4 means three phase with neutral. 3, 4 means both kinds are used.

PART 5 Worked examples

Read the question, think about it, then press Show answer.

Example 1: Which wires does a 3-wire three-phase supply have?

L1, L2 and L3. There is no neutral.

Example 2: The country list shows 4 in the Wires column. What does it mean?

Three phase with neutral: L1, L2, L3 and N.

Example 3: A 380/220 V system. What does a voltmeter read between L1 and L2? Between L1 and N?

L1 to L2 (two phases): 380 V
L1 to N (phase and neutral): 220 V

Example 4: Is a lamp in a house single phase or three phase?

Single phase: it connects between one phase and the neutral.

Example 5: Your machine is rated 400 V, 50 Hz. Will it match Canada?

No. Canada lists 120/208 V, 240 V, 480 V and 347/600 V at 60 Hz, so neither the voltage nor the frequency matches.

PART 6 Quick quiz

Fourteen questions to check what you learned.