What Is a Fluorescent Ballast?

Updated: August 28, 2025

~7 min read • ~1,500 words • Flesch ~60

TL;DR: A ballast limits current and manages starting for fluorescent lamps. For service work on Long Island, verify lamp type, input voltage, ballast factor, start method, and environment. Follow NEC 2023 Articles 410.6, 410.10, 410.36(B), 410.71, and 110.3(B). Use listed components, add a disconnect where required, and plan around future LED retrofits. Programmed start protects lamps with frequent switching. Keep EPA rules in mind for old magnetic units that may contain PCBs. Stock common T8 and T5HO electronic ballasts, lampholders, and quick-disconnects. Test with a meter and label everything.

Why it matters on the job

A fluorescent ballast limits current and provides the right voltage profile to start and run the lamp. Without it, the arc would run away, overheat the tube, and trip breakers or worse. For Long Island jobs, many schools, retail strips, and municipal buildings still run T12, T8, and T5. Knowing how to identify, replace, or retire ballasts saves call-backs and helps with energy compliance. If you are planning maintenance rounds or a partial retrofit, start by confirming the ballast type and wiring so you can stock the right parts and avoid extra trips. See our current selection of ballasts and drivers if you need fast replacements during service work.

Fundamentals

What a ballast does

Fluorescent lamps are negative-resistance devices. Once the arc strikes, current increases unless something limits it. The ballast limits current and sets open-circuit and preheat voltages so the lamp can start, then it stabilizes lamp current during operation.

Magnetic vs electronic

Older magnetic ballasts use inductors and operate at 60 Hz. They are heavier, run hotter, and often buzz. Modern electronic ballasts use solid-state switching to operate lamps at high frequency, typically 20 kHz or higher, which reduces flicker and improves efficacy. Many legacy magnetic types were effectively eliminated by federal efficiency rules; if you still see them, plan an upgrade during your next relamp cycle [1]. For a practical comparison of behavior in the field, see electronic fluorescent ballasts vs magnetic.

Start methods

• Preheat uses starters to warm cathodes before the arc forms. Mostly obsolete in commercial service.
• Rapid start heats cathodes continuously for smooth starts and longer lamp life.
• Programmed start preheats to a target temperature, then applies strike voltage. Best for frequent switching and occupancy sensors.

Where ballasts are used

Common with linear T12, T8, T5, U-bends, and circline lamps. Nameplates list lamp types and counts, input voltage, frequency, ballast factor, and wiring diagram. Photograph the label before you pull it.

Code & compliance (NEC 2023)

• Listing: Luminaires, lampholders, and retrofit kits must be listed. See NEC 410.6. Install and use per the listing and instructions per 110.3(B).
• Disconnecting means: Where required, provide a ballast or driver disconnect so the branch circuit does not have to be opened at the panel. See 410.71. Field-installable connectors help retrofit work; keep ballast disconnect connectors on the truck.
• Environment: Check location ratings for damp or wet areas per 410.10. Use appropriate housings and gasketing.
• Support: Maintain proper luminaire support when opening troffers or strips during ballast swaps. See 410.36(B).
• Legacy PCB ballasts: Pre-1979 magnetic units may contain PCBs. Handle and dispose according to EPA guidance [4]. Do not toss them in job-site dumpsters.

Local adoption and amendments apply. Always verify with the Authority Having Jurisdiction for your town or village on Long Island before finalizing scope.

Selection steps

Step 1: Identify lamp type, wattage, and count

Match the ballast to the exact lamp family and number of lamps per fixture. Examples: F32T8 1-lamp, 2-lamp, or 3-lamp; F54T5HO 1-lamp or 2-lamp.

Step 2: Match input voltage and frequency

Most commercial ballasts are universal 120–277 V, 60 Hz. Verify against the nameplate and the circuit you are landing on.

Step 3: Choose ballast factor

Ballast factor (BF) sets lumen output for a given lamp. Typical values are 0.77 (low), 0.88–0.90 (normal), and 1.15 (high). Use low BF for corridors and normal BF for general office lighting. High BF is for high ceilings or task zones.

Step 4: Select start method and controls

Use programmed start with occupancy sensing or frequent on/off cycles to protect lamp cathodes. Rapid start is fine for timed schedules.

Step 5: Check temperature and environment

For cold rooms or loading docks, verify minimum starting temperature on the spec sheet. Choose ballasts listed for damp or wet locations when required.

Step 6: Plan the retrofit path

If LED is on the horizon, avoid overspending on specialty ballasts. When you do convert, use listed retrofit kits or follow lamp listing. UL 1598C defines retrofit kit scope [3].

Sizing and configuration examples

Example 1: 2-lamp F32T8 troffer at 120 V

• Manufacturer input power for a typical normal-BF electronic ballast: ≈59 W total for two F32T8 lamps.
• Power factor: 0.95 (check nameplate).
• Input current: I = P ÷ (V × PF) = 59 ÷ (120 × 0.95) = 59 ÷ 114 = 0.5175 A. Round to 0.52 A.
• Continuous load on 20 A circuit at 80 percent: 16 A available.
• Max fixtures per circuit: 16 A ÷ 0.52 A ≈ 30. Use 30 fixtures to stay below limits.

Example 2: 2-lamp F32T8 troffer at 277 V

• Same ballast input power: ≈59 W, PF 0.95.
• Input current: I = 59 ÷ (277 × 0.95) = 59 ÷ 263.15 = 0.224 A. Round to 0.22 A.
• Max fixtures on a 20 A lighting circuit at 80 percent: 16 ÷ 0.224 ≈ 71. Cap at 71 fixtures if voltage drop and switching gear allow.

Ballast factor and light levels

If an area was designed around normal BF 0.88, switching to low BF 0.77 changes lumens by 0.77 ÷ 0.88 = 0.875, about a 12.5 percent drop. High BF 1.15 gives 1.15 ÷ 0.88 = 1.31, roughly a 31 percent bump. Confirm photometrics before changing BF in occupied spaces.

Installation and wiring notes

• De-energize and verify absence of voltage before opening the wiring compartment.
• Support the luminaire per NEC 410.36(B) when working in grid ceilings. Do not let it hang by conductors.
• Follow the nameplate diagram. Lead colors and counts vary by model and lamp count.
• Replace damaged lampholders and sockets. See fluorescent lamp holders.
• Add a disconnect where required by NEC 410.71 to simplify future service. Stock field-installable ballast disconnect connectors.
• Conductor fill and splices: Keep all splices inside the channel. Cap unused leads. Maintain the equipment grounding conductor.
• Environment: Match damp or wet location ratings per NEC 410.10. Use gaskets and lensing where required.
• Listing and instructions: Install per NEC 110.3(B) and 410.6. Do not mix unlisted parts.
• Legacy magnetic removal: Pre-1979 magnetic ballasts may contain PCBs. Follow EPA procedures for removal and disposal. Do not landfill [4].

Testing, commissioning, and documentation

• Visual check: Verify lampholder tension and that lamp pins are fully seated. Look for end blackening that suggests wear.
• Meter checks: Measure input current and compare to nameplate within about ±10 percent under steady operation. For quick diagnostics, keep multimeters and testers on hand.
• Function test: Confirm programmed-start timing where specified and dimming range if using a dimmable ballast.
• Controls integration: With occupancy sensors, prefer programmed start to protect cathodes from frequent switching.
• Labeling: Mark inside the housing with date, ballast model, lamp type, BF, and input voltage. Update panel schedules and as-builts.
• Retrofit planning notes: If LED conversion is planned, document spacing, ceiling heights, and target footcandle levels. When installing LED retrofit kits later, ensure they are listed for the luminaire and within the scope of UL 1598C [3].

Local amendments and AHJ interpretations vary across Nassau and Suffolk counties. Confirm details with your inspector before closing ceilings.

Troubleshooting

• Flicker or strobe: Verify lamp seating and lampholder tension. Check input voltage and swap in known-good lamps. If programmed start is specified but starts are instant, the ballast may be wrong for the lamp family.
• No start: Confirm line voltage at ballast input, then check open-circuit voltage at the lamp leads per the datasheet. Inspect for broken tombstones and damaged wiring in the channel.
• One-lamp out in a multi-lamp fixture: Many ballasts shut down a channel when they sense a fault. Replace the suspect lamp first. If the fault follows the channel, replace the ballast.
• Buzzing: Tighten mounting screws and confirm isolation pads. Persistent noise usually points to aging magnetic units. Plan a replacement with electronic gear and document the change order.
• Frequent lamp burnout: Mismatch between start method and controls, overtemperature, or wrong ballast factor. Use programmed start with occupancy sensors and confirm ambient limits.

Not sure whether it’s the lamp or the ballast? Here are signs it’s time to replace a ballast or driver to help triage quickly.

Common mistakes

• Mixing lamp types on a multi-lamp ballast or ignoring the ballast’s lamp list.
• Leaving unused leads uninsulated inside the channel.
• Skipping the disconnect required by NEC 410.71 during retrofit.
• Installing in damp locations without the correct luminaire rating per NEC 410.10.
• Failing to follow listing and instructions as required by NEC 110.3(B) and 410.6.
• Discarding pre-1979 magnetic ballasts with regular trash. Treat as potential PCB waste and follow EPA guidance [4].

Parts to stock + Shop at Revco

• Common electronic ballasts for F32T8 and F54T5HO in low, normal, and high ballast factor.
• Ballast disconnect connectors for safe servicing.
• Fluorescent lampholders and channel covers.
• Clamp meters and multimeters for load checks.
• Fluorescent lamp recycling kits and job box liners.
• LED T8 lamps (UL Type A/B) for phased retrofit strategies.

Need gear in a hurry? Browse our ballasts and drivers category or call for branch pickup options.

When to call the AHJ or an engineer

• Large area relights that change connected load or controls sequences.
• Retrofits in damp or wet locations, or any hazardous location classification.
• Historic buildings or schools with possible PCB magnetic ballasts. Coordinate disposal and documentation with the municipality.
• When combining controls with emergency egress lighting. Confirm listing and transfer behavior.

Long Island jurisdictions interpret details differently. Check with your town or village inspector before you close ceilings.

Safety disclaimer

Only qualified persons should service luminaires. De-energize and verify absence of voltage before opening any wiring compartment. Follow manufacturer instructions and all applicable codes. When in doubt, stop and contact the AHJ.

FAQ

• Do I have to replace lamps when I replace a ballast? It’s smart to. Aging lamps can mask ballast problems and shorten new ballast life.
• Can I dim all fluorescent ballasts? No. You need a ballast listed for dimming and compatible controls. Verify the dimming method and range on the datasheet.
• Why do lamps blacken at the ends? Cathode wear from starts and heat. Programmed start with sensors reduces this.
• Are magnetic ballasts illegal? Many older types were eliminated by efficiency rules, and production largely ceased. Existing installed units can be replaced, but upgrading saves energy [1].
• Can I swap a T12 ballast into a T8 fixture? No. Match the ballast to the lamp family and count exactly.
• What’s the fastest way to tell if a ballast is bad? Verify line voltage, swap in known-good lamps, and compare input current to nameplate. If readings are off and wiring is correct, replace the ballast.

About Revco Lighting & Electrical Supply

Since 1978, Revco Lighting & Electrical Supply has been helping professionals bring their projects to light—literally. As a go-to source for lighting and electrical products across Long Island, NY and nearby areas, we specialize in supporting contractors, builders, and industry experts with practical solutions and dependable service. Whether it’s a complex commercial build or a simple residential upgrade, we’re here to make sure you have what you need, when you need it.

Credits

Author: Revco Editorial Team — Electrical Content Editor

Technical review: Pending — add approved name/credential

Contact: (631) 283-3600

Sources

1. [1] U.S. Department of Energy, “Energy Conservation Program: Energy Conservation Standards for Fluorescent Lamp Ballasts,” Federal Register, 76 FR 70548. Retrieved August 2025.
2. [2] NEC 2023, Article 410.71 overview. Electrical License Renewal. Retrieved August 2025.
3. [3] UL, “UL 1598C LED Retrofit Kits.” UL Standards. Retrieved August 2025.
4. [4] U.S. EPA, “Disposal of Fluorescent Light Ballasts (FLB).” EPA.gov. Retrieved August 2025.