Dimmer switches shutting off??????please help

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I have 4 individual cages, all with thier own wired flexwatt. I have double checked all the wireing to ensure it is correct.

The problem I am having is with the dimmer switches, they will just shut off with no reason. I have tried 2 different brands now, one from home depot and one from Rona, both just turn off with the knob still in the on position???? To reset them I just turn the dial to full for a couple seconds, then back to where it was, and then they come back on??

Anyone have any input on how I can avoid this??? or any brands that work properly??