I have to install some zenon pucks behind a bunch of glass doors and for undercabinet lighting (15 total). I am having trouble determining what size conductor to run from the transformers to the lights. The farthest light will be about 18 feet from the transformers. The salesman at the electrical supply house was totally clueless this afternoon, he said they don't sell many pucks most people apparantly buy them from the big box stores. Any advise will be greatly appreciated.