XR Expansion Boards have no on-board brains. They are entirely reliant on the brains of a "master" device. A master device is an NCD controller with an XR expansion port and a microprocessor of some kind. Some master devices are wireless, and some master devices have digital I/O and analog to digital conversion capabilities. Some master devices also have on-board relays. When you run out of relays, just plug in an XR expansion controller that is equipped with the kind of relays you need.
The product manual for various NCD master devices will refer to a group of 8 relays as a relay bank. XR Expansion Modules count as 1, 2, 3, or 4 banks, depending on how many relays are on board (8, 16, 24, or 32).
As you continue to chain XR relay expansion controllers onto an XR expansion port, the total number of available relay banks will increase. Each master device is only capable of controlling a fixed number of relay banks. You should review the product manual of the master device you are using to determine the maximum number of supported relays banks. This modular expansion approach will allow you to chain relays of all kinds to a single NCD device.
XR Expansion Boards include a 6" ribbon cable with a keyed connector, used to link the expansion controller to an NCD device. At the other end of the relay expansion board is an XR Pass-Through connector, allowing you to chain additional relay banks.