You are going to have to double check the data/instruction sheet for the dimmer packs. It may very well be that they are rated for 1200W per channel, 4 channels, but at less than 3600W _total_ output at any one time. Or it may be the case that being on a dimmer pack lets one consider the lighting 'non continuous'...or it may be the case that the dimmer pack has a built in controller that limits the output power to be less than 3600W for > 3 hours. Or it may be an error in the listing.
I would certainly double check prior to putting the dimmer pack on OCPD > the 20A listed in the instructions. It is possible that the unit is listed only for use on a 20A circuit.
-Jon
