Electrical 101

Ballast Wiring

Grounding a Ballast

Grounding a ballast is very important. Grounding is usually automatic if the light fixture is grounded properly.

A ground wire from the power source should be connected to a light fixture. A metal ballast mounted to the metal light fixture will automatically ground the ballast.

If a ballast has a ground terminal on it, a ground wire should be connected to it.

Fluorescent Ballasts

Ballast Wiring

Instant Start Wiring

Rapid Start Wiring 1 to 3 Lamps

Rapid Start Wiring 4 Lamps

Dimming Ballast Wiring

CFL Ballast Wiring

Emergency Ballasts

Tombstone Lampholders

Fluorescent Tombstone Wiring

Instant Start Tombstone Wiring

Rapid Start Tombstone Wiring 2 and 4 Lamps

Rapid Start Tombstone Wiring 3 Lamps

Swap Terminals on Non-Shunted Tombstones

Fluorescent tubes require a ballast to operate. A fluorescent tube circuit includes a ballast, wires, lampholders, and the tubes.

Rapid Start vs Instant Start Ballasts

When replacing a ballast in a light fixture, it is important to know what type of ballast you are replacing. The two most common types of ballasts are instant start and rapid start. The wiring on these two types are very different. A rapid start ballast has about twice the number of lamp wires than an instant start. The wire colors are also different.

When a rapid start ballast (wired in series) operates multiple lamps and one lamp fails, the circuit is opened and the other lamps will not light.

When an instant start ballast (wired in parallel) operates multiple lamps in a circuit, the lamps operate independently of each other. If one lamp fails, the others can keep operating as the circuit between them and the ballast remains unbroken.

With some 3 and 4-lamp programmed start ballasts (wired in series-parallel), if a single lamp in one branch fails, the lamp(s) in the parallel branch will continue to operate.

Rapid start ballasts can only be wired in series according to the diagram on the ballast.
Instant start ballasts can only be wired in parallel according to the diagram on the ballast.

Changing the wiring on a fluorescent light fixture from rapid start to instant start, involves changing the wiring from series to parallel.

3 total lamp wires, 2 blue and 1 red.

6 total lamp wires, 2 blue, 2 red and 2 yellow.

2 Lamp Rapid Start Ballast Diagram

2 Lamp Instant Start Ballast Diagram

Ballast Wire Colors

Wire colors for individual and common connections on fluorescent ballasts will vary depending on ballast type, brand, and the number of lamps they support. Ballasts have certain colors for individual wires to lampholders, and other colors for common wires to holders.

Magnetic vs Electronic Ballasts

Older magnetic fluorescent ballasts are usually rapid start and wired in series. Newer electronic ballasts are instant start (wired in parallel), rapid start (wired in series), programmed start (wired in series-parallel, dimmable and CFL ballasts.

Bulb vs Lamp

Electricians usually refer to a light bulb as a lamp. Light bulb manufacturers use the term “lamp” when referring to fluorescent lights. On this page, we will refer to a fluorescent light bulb as a lamp or tube.

Individual vs Common Ballast Wires

Individual ballast wires each connect to a lampholder on one side of each tube. The common wire(s) connect to all of the lampholders on the other side of the tubes.