You can put many more than 3 shelves per dimmer, since it handles up to 600w and the 3" heat tape is something like 8 or 10w per foot. I did 3 shelves per dimmer, because heat rises and if all were on the same dimmer, you'd have cooler bottom shelves than top shelves. I can control the top 3 and bottom 3 independently this way.

On the back of your dimmer, you'll have two or three wires coming out. If you have three, tape up the green one (ground) and use the other two to attach to your cord. When you wire the heat tapes together, you can put both wires into one clip; it's wide enough. Here's a pic of how mine are wired.

I have to rewire another of my racks tomorrow, so I'll try to take a pic for you.

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Rob Jenkins
http://herpcam.com

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