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How to Replace 3 Lamp Series-Parallel Ballast with Series

Question or Comment?

One of our readers wrote us about replacing some T8 Motorola 3 lamp series-parallel ballasts (first image below). I suggested he replace them with 3 lamp parallel instant start ballasts. Unfortunately, this involved removing (or replacing) and rewiring the lampholders. He was looking for a solution that did not involve replacing or rewiring lampholders.

He was able to locate a 3 lamp series ballast (second image below). Just to see if it might work, he wired the new ballast to the fixture lampholders while matching colors (third image). As it turns out, the lamps lit up and are still on.

This reader David is a retired electrician and doing volunteer work at the local library.

3 Lamp Series-Parallel Ballast

Factory wiring

3 Lamp Series-Parallel Ballast

3 Lamp Rapid Start Ballast Wiring Diagram

Replacement ballast

3 Lamp Series Ballast Wiring Diagram

6 Individual wires, 2 common wires

After 3 Lamp Ballast is Replaced with Rapid Start

As seen below, the wire colors on the ballast match the wire colors on the lampholders. Orange wire connectors are preferred for joining 4 ballast wires (18 AWG).

3Lamp Seriesparallel to Series Lampholder Wiring Diagram