ProXR controllers (excluding ProXR Lite) include a XR Relay Expansion port.  This expansion port allows you to control more relays by adding expansion boards.  The XR port allows you to mix high-power and low-power relays together.  Easily add or mix signals relays, power relays, and solid state relays using the XR Expansion port.  ProXR controllers provide firmware support for control of 64 relay banks (512 relays).  However, it should be stated that due to EMI and cable distance limitations, it may not be possible to achieve a full 512 relay configuration.  As a general rule, the XR bus should extend no more than 3 feet from the main controller.  This length includes cabling AND the length of the relay expansion boards added together.  Anything beyond 3 feet should be considered experimental, and may prove unreliable for some applications.