Generator Symbol
Definition: The Generator symbol represents an electromechanical device that converts mechanical energy into electrical energy using electromagnetic induction, shown in circuit diagrams and single-line diagrams as a circle (per IEC 60617 and ANSI Y32.2 / IEEE 315) with L1 (l1) and L2 (l2) output terminals for the generated voltage.
Also known as: genset, standby generator, backup generator, alternator, emergency generator, AC generator, diesel generator, portable generator.
What the Generator symbol means
The Generator symbol denotes an electrical machine that produces AC or DC voltage by rotating a conductor in a magnetic field (Faraday's law of electromagnetic induction). In schematic and single-line diagrams, the generator symbol appears to identify a power source that is independent of the utility grid — typically a diesel, gasoline, natural gas, or propane engine driving a synchronous alternator.
The two output terminals — L1 (l1) and L2 (l2) — represent the two output lines of a single-phase generator or two phases of a multi-phase machine. In single-line diagrams, additional terminals (L3, neutral, ground) may be shown for three-phase generators. The generator symbol is central to standby power system drawings, transfer switch diagrams, and generator room layout plans.
How to identify the Generator symbol
The generator symbol is drawn as a circle with the letter G (or G~ for AC generator, G= for DC generator) inside. In IEC 60617, an AC generator is shown as a circle containing a sine wave symbol (~) or the letter G with a tilde. In ANSI Y32.2 / IEEE 315, the generator is a circle with G inside. Output terminals L1 (l1) and L2 (l2) emerge from the circle as lines connecting to the output wiring or to the automatic transfer switch (ATS) in standby power applications.
Function in a circuit
A generator produces electrical power by rotating a shaft driven by a prime mover (diesel engine, gasoline engine, gas turbine, steam turbine, water turbine) past a set of electromagnets or permanent magnets. For a synchronous AC generator (alternator), the rotor carries the field winding (energised by a separate DC exciter) and the stator carries the output windings. As the rotor spins, alternating EMF is induced in the stator at a frequency determined by the rotational speed and number of pole pairs (f = N × P / 120, where N is RPM and P is poles). A voltage regulator (AVR) maintains constant output voltage by adjusting field current as load changes.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-08 defines the generator symbol as a circle with a sine wave or 'G' qualification symbol for AC machines. IEC 60034 (Rotating Electrical Machines) governs generator performance, ratings, and testing. IEC 60950 / IEC 62040 cover generator-based UPS and standby systems. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 represents the generator as a circle with the letter G inside. IEEE Std 115 (Test Procedures for Synchronous Machines) and IEEE Std C50.13 (Requirements for Cylindrical-Rotor Synchronous Generators) govern generator design and testing. NFPA 110 (Standard for Emergency and Standby Power Systems) governs standby generator installation in North America. |
| Key difference | IEC 60617 uses a circle with a sine wave (~) for AC generators, clearly distinguishing AC from DC (which uses a straight line or = symbol). ANSI Y32.2 / IEEE 315 uses a plain G inside a circle for generators, with AC or DC distinguished by annotation. Both symbols use a circle body; the key difference is the internal qualifier symbol for AC vs DC machines. |
Terminals / pins
| Pin | Name |
|---|---|
| l1 | L1 |
| l2 | L2 |
Typical values
Output power: 1 kW (portable) to over 1,000 MVA (power plant turbine generators); voltage: 120/240 V single-phase (residential), 480 V three-phase (commercial/industrial), 4.16 kV to 25 kV (utility-scale); frequency: 50 Hz or 60 Hz; power factor: typically 0.8 lagging rated; fuel: diesel, natural gas, propane, gasoline; prime power efficiency: 30–45% (diesel); starting method: electric motor (12 V or 24 V DC).
Where the Generator symbol is used
- Standby power systems: emergency generator with automatic transfer switch (ATS) provides backup power to hospitals, data centres, and critical facilities on utility failure
- Residential backup power: 7–22 kW standby generator on L1 (l1) and L2 (l2) outputs connected to an ATS protecting the main panel
- Construction sites: portable diesel generators supply temporary power for tools, lighting, and equipment on sites without utility connection
- Marine and offshore platforms: onboard generator sets power ship electrical systems and drilling equipment
- Telecommunications towers: standby generators maintain cellular and communications equipment during utility outages
- Single-line diagrams and power system studies: generator symbols define power sources in load flow, short-circuit, and protection coordination analyses
Example
In a residential standby power system drawing, the generator symbol (circle with G) has L1 (l1) connected to one pole of a 200 A automatic transfer switch and L2 (l2) to the other. When the utility fails, the ATS signals the generator to start; after the engine reaches rated speed and voltage (240 V AC, 60 Hz), the ATS transfers the load from utility to generator within 10 seconds. A natural gas line from the house supply feeds the generator engine, allowing indefinite runtime.
Key facts
- The Generator symbol is a circle with 'G' or 'G~' inside, representing an electromechanical source of electrical energy; IEC 60617-08 uses a circle with a sine wave for AC generators, ANSI Y32.2 uses a circle with G.
- The two output terminals are L1 (l1) and L2 (l2), representing the AC output lines; three-phase generators add L3 and neutral terminals.
- Generator output frequency is determined by the formula f = N × P / 120, where N is rotor speed in RPM and P is the number of poles; a 4-pole generator must rotate at 1,500 RPM (50 Hz) or 1,800 RPM (60 Hz).
- An Automatic Voltage Regulator (AVR) maintains constant generator output voltage (within ±1–2%) as electrical load changes by adjusting the rotor field excitation current.
- Standby generators in North America are governed by NFPA 110, which specifies transfer time, testing requirements, and fuel storage for emergency and legally required standby systems.
- Generator kVA rating is the apparent power the machine can deliver; kW (active power) = kVA × power factor (typically 0.8 rated, so a 50 kVA generator delivers 40 kW at rated pf).
- Generator paralleling (connecting two or more generators to a common bus) requires synchronisation of voltage magnitude, frequency, phase angle, and phase sequence before closing the paralleling breaker.
Diagrams that use this symbol
- circuit diagram generator
- dc generator diagram
- changeover switch wiring diagram
- generator connection diagram
- generator wiring diagram
- ats diagram
- ats wiring diagram
- automatic transfer switch wiring diagram
Frequently asked questions
What does the generator symbol mean in a circuit diagram?
The generator symbol represents an electromechanical source of electrical power — a machine that converts mechanical energy from a prime mover (engine, turbine) into AC or DC voltage. It appears in circuit and single-line diagrams to identify an independent power source such as a standby genset or alternator.
What does the generator symbol look like?
The generator symbol is a circle with the letter G inside. For an AC generator, IEC 60617 adds a sine wave symbol (~) inside the circle. ANSI Y32.2 / IEEE 315 uses a plain G. Output terminals L1 (l1) and L2 (l2) emerge from the circle as connection lines.
What is the difference between a generator and an alternator?
An alternator is a type of generator that produces alternating current (AC) from a rotating magnetic field on the rotor inducing EMF in a stationary stator winding. A DC generator (dynamo) uses a commutator and brushes to convert the internally-generated AC into DC at the output terminals. In common usage, 'generator' refers to the complete engine-driven power unit, while 'alternator' specifically describes the AC-generating machine inside it.
What is the IEC standard symbol for a generator?
Per IEC 60617-08, an AC generator is represented as a circle containing a sine wave symbol (~). A DC generator is shown as a circle with a straight horizontal line or 'G=' inside. The output terminals connect as labelled lines from the circle boundary.
What size generator is needed for a house?
A whole-house standby generator for a typical North American single-family home requires 14–22 kW to power all critical loads (HVAC, well pump, refrigerator, lighting, and outlets). A partial-house protection system covering essential loads only may use 7–12 kW. Generator sizing is calculated by summing the running wattage of all loads plus the highest starting surge (motor loads have 2–3× running current at start).
What standard governs standby generator installation?
In North America, NFPA 110 (Standard for Emergency and Standby Power Systems) governs installation, testing, and maintenance of standby generators in buildings. NEC Article 445 covers generator wiring, and NEC Article 702 covers optional standby systems. Internationally, IEC 60038 and IEC 62040 series cover standby generator and UPS installation requirements.
How is a generator connected to a house electrical system?
A standby generator connects to the house electrical system via an Automatic Transfer Switch (ATS). The ATS monitors utility power and, on failure, starts the generator, waits for it to reach stable voltage and frequency, then transfers the panel load from utility to generator via the L1 (l1) and L2 (l2) output terminals. Manual transfer switches are also used for portable generators, though NEC requires these to prevent backfeed to the utility.
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