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Fluorescent Ballast Wiring

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

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 the lampholders on the other side of the tubes.

2 Lamp Parallel Wiring 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 wired in series. Newer electronic ballasts are usually wired in parallel, except for rapid start, programmed start, and dimmable ballasts.

Series vs Parallel Ballasts and Wiring

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

When a parallel (instant start) ballast 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 series-parallel ballasts, if a single lamp in one branch fails, the lamp(s) in the parallel branch will continue to operate.

1 Lamp Series Ballast Diagram

1 Lamp Parallel Ballast Diagram

1 Lamp Series Ballast1 Lamp Parallel Ballast

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.