I think the rule of three is on the safe side of things. I'm sure the rule is different between some brands of lights. All of the incans that I have say I can connect up to 5 sets together total. If you lights still have the tag on the end see if it has a max amp rating listed. Most 100 light sets run around 40 watts. My lights say I can connect up to 218 watts to them.

Dale P.