Single-Phase Motor Symbol
Definition: The Single-Phase Motor symbol represents an AC electric motor powered by a single-phase supply, depicted in IEC 60617 as a circle containing the letter M (motor designator) with two supply terminals labelled Line and Neutral, used in residential appliance, pump, and fan circuits operating at 120 V or 240 V single-phase AC.
Also known as: 1-phase motor, single-phase AC motor, single-phase induction motor, split-phase motor, capacitor-start motor, M symbol (single phase).
What the Single-Phase Motor symbol means
The Single-Phase Motor symbol represents an electric motor that operates from a two-wire single-phase AC supply. The symbol appears in wiring diagrams wherever a motor is driven by residential or light-commercial 120 V or 240 V single-phase power, such as in HVAC, pumps, compressors, and household appliances.
The symbol communicates that the load is a rotating machine requiring a single-phase AC line voltage and a neutral return. In schematic terms, the circle-M symbol tells the reader that the device converts electrical energy into mechanical rotation and that its full-load current, starting current, and protection requirements differ significantly from those of a resistive or capacitive load.
How to identify the Single-Phase Motor symbol
The Single-Phase Motor symbol is drawn as a circle with the letter M (or 'M~' to indicate AC) inside. Two terminals emerge from the top of the circle: Line (L) on the left side and Neutral (N) on the right side. Some variants show the motor rated voltage and power class (e.g. '1~ 240 V') alongside the symbol. The circle differentiates motor symbols from transformer (two circles/coils) and generator symbols.
Function in a circuit
A single-phase AC motor converts single-phase alternating current electrical energy into mechanical rotational energy. Because a single-phase supply alone cannot produce a rotating magnetic field, single-phase motors use auxiliary starting methods: split-phase (auxiliary winding), capacitor-start (phase-shifted capacitor winding), capacitor-start/capacitor-run, or shaded-pole. Once running, the motor maintains rotation via the main winding. Typical applications involve constant-speed loads such as fans, pumps, compressors, and small conveyors.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-06 defines the general motor symbol as a circle with 'M' inside; IEC 60034 series governs rotating electrical machine ratings and performance. Single-phase type is indicated by the annotation '1~' (one-phase AC) adjacent to or inside the circle. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315-1975 uses the same circle-M symbol for a general motor. Single-phase type is indicated by labelling or context (Line and Neutral terminals); the standard does not use '1~' notation, relying on adjacent text instead. |
| Key difference | IEC 60617 annotates the motor circle with '1~' to explicitly denote single-phase AC; ANSI/IEEE 315 uses the same circle-M without the phase annotation, relying on terminal labels and title-block supply information to convey single-phase operation. Both use an identical circle-M glyph. |
Terminals / pins
| Pin | Name |
|---|---|
| l | Line |
| n | Neutral |
Typical values
Typical ratings: 120 V or 240 V AC single-phase, 50 Hz or 60 Hz; power range from 1/20 hp (small fans) to 5 hp (pump/compressor); full-load current: 1 A–25 A depending on rating; starting current: 5–8× full-load current; power factor: 0.7–0.9 lagging.
Where the Single-Phase Motor symbol is used
- HVAC systems: single-phase induction motors drive residential air-handler fans and outdoor condenser fans
- Water pump circuits: single-phase capacitor-start motors drive well pumps and irrigation pumps
- Domestic appliances: washing machines, dishwashers, and refrigerator compressors use single-phase motors
- Garage door openers and gate operators in residential wiring diagrams
- Workshop machinery: single-phase motors drive small drill presses, lathes, and grinders
- Sump pumps and sewage ejector pumps in residential plumbing/electrical drawings
Example
In a residential pump control circuit, the Single-Phase Motor symbol (circle-M with Line and Neutral terminals) represents a 1 hp, 240 V single-phase well pump. The Line terminal connects through a motor protection circuit breaker to the 240 V hot conductor; the Neutral terminal returns to the panel neutral bar. A float switch in series with the Line conductor starts and stops the motor automatically based on tank level.
Key facts
- The Single-Phase Motor symbol is a circle with the letter M inside, with Line (L) and Neutral (N) terminals at the top, per IEC 60617-06.
- The standard reference designator for a motor in schematics is M (e.g. M1, M2).
- Single-phase motors require an auxiliary starting mechanism (capacitor-start, split-phase, or shaded-pole) because a single-phase supply alone cannot produce a rotating magnetic field.
- Typical supply voltages are 120 V AC (North America) or 240 V AC (Europe/Australia/UK), at 50 Hz or 60 Hz.
- Starting current for a single-phase induction motor is typically 5–8 times the full-load running current, which must be considered when sizing overcurrent protection.
- IEC 60034-1 governs ratings for single-phase rotating machines; motor wiring diagrams must show the protection device (MPCB or fuse) in the Line conductor.
- Common single-phase motor types used in wiring diagrams include: capacitor-start, capacitor-start/capacitor-run (CSCR), split-phase, permanent-split capacitor (PSC), and shaded-pole.
Diagrams that use this symbol
- fan connection with capacitor
- electric motor diagram
- simple motor diagram
- single phase motor wiring diagram
- single phase motor connection diagram
- 1 phase motor connection
- ceiling fan connection with capacitor
- single phase motor connections
Frequently asked questions
What does the single-phase motor symbol look like?
The single-phase motor symbol is a circle with the letter M inside. Two terminals emerge from the top: Line (L) on one side and Neutral (N) on the other. IEC drawings may annotate the circle with '1~' to indicate single-phase AC.
What does the single-phase motor symbol mean in a wiring diagram?
The single-phase motor symbol means the circuit contains an AC motor powered by a single-phase (two-wire) supply. It represents a device that converts single-phase AC electrical energy into mechanical rotation, such as a pump, fan, or compressor motor.
What is the designator letter for a motor in schematics?
The reference designator for any motor in a schematic is M (e.g. M1, M2), per ANSI Y32.2 / IEEE 315 and IEC 60617. Single-phase motors are distinguished from three-phase types by terminal count and the '1~' annotation.
What is the difference between the single-phase and three-phase motor symbol?
The single-phase motor symbol (circle-M) has two supply terminals: Line and Neutral. The three-phase motor symbol (also circle-M) has three terminals: U, V, and W. IEC drawings annotate the single-phase version with '1~' and the three-phase version with '3~'.
What standard defines the motor symbol?
The motor symbol is defined in IEC 60617-06 (IEC standard for electromechanical devices). The equivalent ANSI standard is ANSI Y32.2 / IEEE 315-1975. Both use a circle with M inside as the general motor symbol.
Why do single-phase motors need a capacitor?
Single-phase AC cannot generate a rotating magnetic field by itself. A capacitor-start or capacitor-run single-phase motor uses a capacitor to create a phase-shifted current in an auxiliary winding, producing a two-phase rotating field needed to start and run the motor.
What protection device is shown with a single-phase motor symbol?
In wiring diagrams, a single-phase motor is typically protected by a motor protection circuit breaker (MPCB), a thermal overload relay, or a fuse in the Line conductor. The protection symbol appears in series with the motor symbol's Line terminal.
Place the Single-Phase Motor symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.