The 2638A-20CHKIT consists of one 2638A-RLY extra relay card (4410452) and one 2638A-100 universal input connector (4410418). This kit allows for easy 20-channel user-installable expansion for your 20- or 40-channel model or an extra backup relay card and input module for your 60-channel system. These kits may be installed by the user without the need for recalibration.