A man working for an outside contractor was knocked out early Monday morning while doing maintenance at Exelon Nuclear’s Limerick Generating Station. He was unconscious for about a minute.  The Nuclear Regulatory Commission says the man hit his head on a scaffold pole while climbing a ladder in the secondary containment area at Unit Two, which is shut down for re-fueling.  The NRC says he was wearing full protective gear and was not contaminated by radiation.  Exelon does other maintenance and repair work when a reactor is shut down for re-fueling, and outside contractors are brought in to help.