In very cold weather I keep my dogs in metal cages (in my shop) with 250 watt heat lamps hanging over the cages. I'm running two lamps off of a generator extension cord connected to my homes exterior outlet. I need to add a third lamp connected to a separate ext cord, but both cords will need to be connected to the same outlet. Will this 750 watt total be too much to run from one outlet? Many thanks.