Luminaires designed for use with one or three linear fluorescent lamps >30W each shall use two-lamp tandem-wired ballasts in place of single lamp ballasts when two or more luminaires are in the same space and on the same control device.

I saw your posting to the International Association of Electrical Inspector's web site today regarding tandem wiring, and can answer most of your questions.

1. Tandem wiring - Tandem wiring is when 2 light fixtures share a ballast. For example, 3-lamp parabolic fixtures are often wired so that the center lamp can be switched separately from the outside 2 lamps. Some refer to this as stepped switching, others as bi-level switching. To step switch two 3-lamp fixtures you would need to use 3-two lamp ballasts. One fixture would have two ballasts. One 2-lamp ballast would control the outboard lamps, and the other 2-lamp ballast would control the center lamp of one fixture, and the center lamp of another. So, this ballast is "shared" between 2 fixtures. Then the other fixture would have one 2-lamp ballast controlling the outside 2 lamps.

2. Why is it in the code? Because it's more energy efficient to use a 2-lamp ballast, rather than many single lamp. For example, a 1-lamp electronic ballast for a 32-watt T8 lamp uses 32 watts. A 2-lamp ballast for the same lamp uses 58 watts. So, 6 watts are saved by using the 2-lamp ballast (32 X 2 = 64 - 58 = 6 watts) In addition, I believe they are trying to encourage step switching as described above.

3. Definition of efficacy - Efficacy - how efficient a lamp is to operate. This is measured in lumens per watt. Lumens is the light output of a lamp. For example, a 32-watt 4 foot T8 lamp puts out about 3200 lumens. Divide this by the lamp watts, and the lamp efficacy is 3200/32 = 100 lumens per watt, or lm/W.


I hope this helps you out. I'm not a member of IAEL, so I couldn't log in to answer your posting on the site. You might find some of our code resources helpful to your work. We have code summaries, and tools for code compliance on our web site at http://www.wattstopper.com/codesmart.html. In addition, we offer education programs on energy codes and LEED, which might interest you. Just check out our Education Programs on our web site. I was just in Ft. Lauderdale last week giving seminars on the Florida code and ASHRAE, and on LEED. I was in Orlando last fall.

Sincerely,

Dorene Maniccia