The Heat Mat Controller Expansion has a 20 A variable AC stage for controlling Hog Hearth Heat Mats. Installation is simple and requires no additional configuration; all Expansion Boxes follow the programs and settings of the main control (HMC-4). The Expansion Boxes for the HMC 4 have two variants. The 2-10A Expansion (HH-HMC-4-EX10) is used to expand 2 individual zones of the HMC 4 by 10 Amps, and the 20A Expansion (HH-HMC-4-EX20) is used to expand 1 zone of the HMC 4 by 20 Amps.