The Large Capacity AT-1 controls up to 120 sq. feet of Agritape on a 20-amp service line. Thermostat features an easy to adjust temperature dial and a bulb sensor with a 2-foot lead. A light indicates when the heat mats are on, and a ground wire connects to the screen that provides system ground. The AT-1 offers four receptacles to plug in heaters, and the AT-JR has two receptacles. More mats can be added by using a 20-amp rated plug-in multi-outlet strip (not provided) in one of the controllers receptacles. An attractive brushed aluminum finish and quality components assure years of service.