4 Relay SPDT Expansion Module
The X-21s™ expansion module is used in conjunction with the X-400 or X-600M™ controller. The X-21s is a multi-function module with four SPDT relays.
One or more X-21s expansion modules can be connected to an X-400 or X-600M controller with a ribbon cable which provides both power and communications.
More information is available on the website of ControlByWeb.