United Illuminating will be conducting system testing at an electrical substation in Fairfield tomorrow.  Between 3am and 5am, customers of Easton, Fairfield and Bridgeport may experience a brief power outage.  The utility says the outage is expected to last less than 5 minutes.  If anyone is dependent on life-saving medical equipment and not registered with United Illuminating as a life-support customer, they are urged to contact the utility.