Fluorescent Light Ballasts - Electrical 101 (2024)

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Electrical 101

Ballast Wiring Diagram

Lamp Compatibility Table

Fluorescent lamps use a ballast which transforms line voltage to a voltage to start up and operate the lamp(s). Newer fluorescent ballasts are usually rated for both 120 volts and 277 volts. Some are rated for only 120 volts, others for only 277 volts (used in commercial environments). Find Fluorescent Ballasts

CFLs for the home have a built-in ballast at the base of the bulb. Commercial CFLs use a separate ballast. Ballasts have a wiring diagram to show how they connect to the lampholders.

There are four basic types of fluorescent ballasts:

Instant start ballasts use a high starting voltage (about 600 volts) to start very quickly (less than 0.1 seconds). There is no preheating of the electrodes for the highest energy efficiency, but are best suited for a limited amount of switching (10,000 to 15,000 switch cycles before failure). Instant start ballasts are wired in parallel. Find Instant Start Ballasts

Rapid start magnetic ballasts are used in T12 and older T8 fixtures and wired in series. These ballasts are usually replace with electronic ballasts. Find Rapid Start Ballasts

Rapid start electronic ballasts heat the electrodes while applying the starting voltage (about 500 volts) to start the lamps quickly in about 0.5 to 1.0 seconds. Electrode heating continues while the lamps are on and consume a little more power (about 2 watts per lamp) than instant start ballasts. They can operate 15,000 to 20,000 switch cycles before failure. Rapid start ballasts are wired in series.

Programmed start electronic ballasts start quickly in about 1.0 - 1.5 seconds. They preheat the electrodes in a controlled manner before applying the starting voltage. Programmed start ballasts minimize electrode stress and maximize lamp life for frequent starting (areas with occupancy sensors). They can operate up to 50,000 switch cycles before failure. Programmed start ballasts are wired in series. Find Programmed Start Ballasts

T8 lamps with a newer electronic ballast use about 20 - 30% less energy than a T12 magnetic ballast. If a T12 magnetic ballast fails, it should be replaced with a T8 electronic ballast. T12 ballasts are available, but T12 lamps are being discontinued. Depending on the light fixture, and how it is mounted, it may be easier and about the same price to replace the fixture instead of the ballast. A new garage fluorescent light fixture could cost less than a replacement ballast.

(4) F32T8

LAMP TYPE

Up to 4 lamps

Fluorescent 32 watts

T8 lamp

Compatible Lamp types for this ballast

Fluorescent Ballast Labels

The label on the ballast shows two important labels.

Lamp compatibility table (type of lamps that can be used with this ballast)
Ballast wiring diagram (shows how the ballast is wired to the lamps)

Fluorescent Tube Diameters

Fluorescent tubes have two common shapes, straight and u-shaped. The most common types are T12, T8, and T5. The T stands for tubular and the number indicates the diameter in 1/8 of an inch. Lamp diameter is determined by ballast type. A fixture with a T12 ballast must use a T12 bulb. A fixture with a T8 ballast must use a T8 bulb, etc.

Matching a Ballast with a Lamp

There are three requirements when matching a ballast to a lamp. In the example above, lamp type F32T8 has the following three requirements:

1. Fluorescent lamp

2. 32 watts

3. T8.

T12 Fluorescent Tubes Discontinued

T12 fluorescent tubes are not made anymore because of poor energy efficiency. While these lamps are still in stock in some stores, replacing the ballast with a more efficient T8 electronic ballast could be a better choice.