http://www.cabl.com/restaurant/electronics.html Or for an easy at a glance calculation just figure 1.5 amp draw for amps and 1.0 for LE's. that will give you some leeway for any temp. change. Example: If you have 15 actives on a 20 amp power supply there is a very good chance you are on the verge of over extending the P.S. and should add one.