Fluorescent / HID Ballast Symbol
Definition: The Fluorescent / HID Ballast symbol represents a current-limiting and arc-stabilising control device for gas-discharge lamps in circuit diagrams, drawn as a labeled rectangular block with four pins — Line In, Neutral In, Lamp A, and Lamp B — standardised under IEC 60617-11 (inductors/reactors) and ANSI Y32.2 / IEEE 315, governing lamp current to enable stable operation of fluorescent, metal-halide, and high-pressure sodium lamps.
Also known as: lamp choke, fluorescent ballast, HID ballast, discharge lamp ballast, lighting ballast, lamp control gear.
What the Fluorescent / HID Ballast symbol means
The Fluorescent / HID Ballast symbol denotes the control gear that limits and regulates the current through a gas-discharge lamp. Without a ballast, a gas-discharge lamp exhibits negative dynamic resistance — as it ignites and conducts, its resistance falls, causing runaway current that immediately destroys the lamp and trips circuit protection. The ballast provides a current-limiting impedance (magnetic choke or electronic feedback loop) that stabilises lamp current at the rated operating value.
In lighting circuit wiring diagrams, the ballast symbol marks the intermediate device between the mains supply (Line In, Neutral In pins) and the lamp(s) (Lamp A and Lamp B output pins). Magnetic ballasts are inductive reactors (chokes); electronic ballasts are switching power supplies operating at 20–50 kHz that additionally eliminate 50/60 Hz flicker and improve efficacy.
How to identify the Fluorescent / HID Ballast symbol
The Fluorescent / HID Ballast symbol is drawn as a labeled rectangular block marked 'BALLAST' or with a stylised choke/inductor symbol inside, with four pin connections: Line In and Neutral In on the left side (mains input), and Lamp A and Lamp B on the right side (lamp output). Some symbols show a separate igniter output for HID lamps. The block representation distinguishes it from a simple inductor coil symbol, reflecting its multi-function control-gear nature.
Function in a circuit
A lamp ballast performs three functions: (1) current limiting — the ballast's inductive or electronic impedance limits lamp current to the rated value, preventing thermal runaway; (2) starting — magnetic ballasts use a starter or auto-transformer action to generate the high-voltage pulse that ionises the lamp gas; electronic ballasts generate high-frequency (20–50 kHz) high-voltage pulses to pre-heat cathodes and strike the arc; (3) power factor correction — electronic ballasts include PFC stages to bring power factor above 0.95, reducing reactive current demand on the mains supply.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60929 (AC electronic control gear for tubular fluorescent lamps) and IEC 61347 series (lamp controlgear) define performance requirements. IEC 60617-11 covers inductor/reactor symbols applicable to magnetic ballasts. The lamp controlgear symbol is often represented as a labeled block per IEC 60617-02. |
|---|---|
| ANSI/IEEE 315 | ANSI C82.1 (ballasts for fluorescent lamps) and ANSI C82.4 (ballasts for HID lamps) specify performance and labeling requirements for North American ballasts. ANSI Y32.2 / IEEE 315 use a labeled block symbol for ballasts in lighting circuit diagrams. |
| Key difference | IEC and ANSI both represent ballasts as labeled rectangular blocks in lighting diagrams. IEC 61347 and ANSI C82 series define performance standards; the schematic symbol conventions per IEC 60617 and ANSI Y32.2 are effectively the same labeled block representation. |
Terminals / pins
| Pin | Name |
|---|---|
| l_in | Line In |
| n_in | Neutral In |
| lamp_a | Lamp A |
| lamp_b | Lamp B |
Typical values
Input voltage: 120 V or 277 V AC (ANSI), 220–240 V AC (IEC). Frequency: 50/60 Hz input; 20–50 kHz output (electronic). Lamp types: T5, T8, T12 fluorescent; 35–1000 W metal-halide; 35–1000 W HPS. Power factor: >0.95 (electronic), 0.5–0.9 (magnetic). THD: <10% (Class A electronic). Operating temperature: −20 °C to +50 °C.
Where the Fluorescent / HID Ballast symbol is used
- Commercial office and retail fluorescent tube fixture wiring (T8, T5 lamps) requiring electronic ballasts for flicker-free, efficient operation
- Street lighting and car park fixtures using HPS (high-pressure sodium) or metal-halide HID lamps
- Sports arena and industrial high-bay lighting using 400 W–1000 W metal-halide HID ballasts
- Retail display case lighting with compact fluorescent lamps (CFL) controlled by integrated or remote ballasts
- Medical facility UV germicidal irradiation (UVGI) systems using specialty fluorescent ballasts
- Grow-light and horticulture lighting systems using HPS or ceramic metal-halide ballasts for plant cultivation
Example
In a commercial office ceiling grid schematic, the Fluorescent / HID Ballast symbol shows its Line In pin connected to the hot conductor of the 277 V branch circuit and Neutral In to the neutral, with Lamp A and Lamp B outputs connecting to the two lamp holders of a 2×28 W T5 fluorescent luminaire. The electronic ballast operates the lamps at 40 kHz, eliminating the 100/120 Hz flicker of magnetic ballasts and achieving a lamp efficacy of 90 lm/W.
Key facts
- The Fluorescent / HID Ballast symbol represents the control gear that limits and stabilises current through a gas-discharge lamp, with four pins: Line In and Neutral In (mains input), and Lamp A and Lamp B (lamp output).
- Without a ballast, a gas-discharge lamp exhibits negative dynamic resistance after arc ignition, leading to uncontrolled current rise and immediate lamp failure.
- Magnetic ballasts are 50/60 Hz inductive chokes that limit lamp current by series reactance; electronic ballasts are switching converters operating at 20–50 kHz that also provide cathode pre-heat, high-frequency arc ignition, and power factor correction.
- Electronic ballasts eliminate 100/120 Hz lamp flicker (which can cause headaches and reduce productivity) by operating the arc at frequencies above 20 kHz — above the human flicker-fusion threshold.
- IEC 61347 series governs lamp controlgear requirements internationally; ANSI C82.1 and C82.4 govern fluorescent and HID ballasts in North America.
- Power factor of electronic ballasts exceeds 0.95 with active PFC, reducing reactive current in building wiring and qualifying for energy efficiency incentives.
- LED drivers (constant-current power supplies for LED luminaires) are the functional successor to ballasts but use a different circuit topology and symbol in modern lighting diagrams.
Diagrams that use this symbol
- dali wiring diagram
- dali dimming wiring diagram
- 2 lamp ballast wiring diagram
- 4 lamp ballast wiring diagram
Frequently asked questions
What does the Fluorescent / HID Ballast symbol mean in a circuit diagram?
The Fluorescent / HID Ballast symbol represents the current-limiting and arc-stabilising control device between the mains supply and a gas-discharge lamp. Its four pins — Line In, Neutral In, Lamp A, and Lamp B — show the mains input connections on the left and the lamp connections on the right, indicating that lamp current is controlled by the ballast rather than connected directly to mains voltage.
What does the lamp ballast symbol look like on a schematic?
The lamp ballast symbol is a labeled rectangular block marked 'BALLAST' or containing a stylised inductor coil or transformer symbol, with Line In and Neutral In pins on the left side and Lamp A and Lamp B pins on the right side. It is drawn as a block (not as a simple inductor coil) to reflect its multi-function control-gear nature encompassing both magnetic and electronic types.
Why do fluorescent lamps need a ballast?
Fluorescent lamps (and all gas-discharge lamps) exhibit negative dynamic resistance after the arc ignites: as the gas conducts more current, the lamp voltage drops, which in a constant-voltage supply causes further current increase — a runaway condition that destroys the lamp in milliseconds. A ballast provides a current-limiting series impedance (inductance or electronic feedback) that stabilises lamp current at the design rating for safe, continuous operation.
What is the difference between a magnetic and electronic ballast?
A magnetic ballast is a 50/60 Hz iron-core inductor (choke) that limits lamp current by series reactance. It causes the lamp to flicker at twice the mains frequency (100/120 Hz) and has a power factor of 0.5–0.9. An electronic ballast is a switching converter operating at 20–50 kHz; it eliminates visible flicker, achieves power factor above 0.95, reduces energy losses by 20–30%, and provides soft-start pre-heating of the lamp cathodes.
What standard defines the lamp ballast symbol?
IEC 61347 series (lamp controlgear) and IEC 60929 (AC electronic ballasts for fluorescent lamps) govern ballast performance internationally. ANSI C82.1 and C82.4 cover fluorescent and HID ballasts in North America. Schematic symbols follow IEC 60617-02 general block conventions and ANSI Y32.2 / IEEE 315 labeled-block conventions.
Can I replace a magnetic ballast with an electronic ballast?
In most cases yes, but the replacement ballast must be rated for the same lamp type, lamp wattage, and supply voltage. Electronic ballasts are wired to the same Line In, Neutral In, Lamp A, and Lamp B connections but may require different wiring if the lamp starting method changes (e.g., switching from preheat start to programmed rapid start). Always verify lamp-ballast compatibility from the manufacturer's lamp compatibility list.
What is the difference between a ballast and an LED driver?
A ballast controls current for gas-discharge lamps (fluorescent, HID) by limiting arc current via inductance or electronic feedback. An LED driver is a constant-current DC power supply that sets the forward current through LED strings, with no arc-stabilisation function. LED drivers have replaced ballasts as fluorescent and HID lamps are superseded by LED luminaires; the two devices are not interchangeable and use different schematic symbols.
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