I'm not an electrician, but I do know that the smaller the wire, the less current it can carry. So, it sounds like your wire was too small for all of the power your lights were pulling. What is your lighting setup? You may try rewiring it so that the power is divided between two or more power cables, or change out the cable to a larger wire size.
For example, in my hood, I have 2 PC ballasts connected to one power line (384 watts total) and 2 MH ballast each with their own power lines (400 watts each). Each of these three plugs then gets plug into its' own wall recepticle. Each power lines is a 14 guage 3 wire cable.