The UR-4CH Digital I/O module is of the ‘4C’ order specification. This specifies that the digital I/O module has 4 solid state MOSFET outputs (current with optional voltage). Since the UR-4CH is a solid state output digital I/O module, this means it is ideal for direct tripping applications because of its fast tripping time, fast reset time, and high current breaking capability. These outputs can be used to control and monitor substation auxiliary equipment and other equipment used for protection applications. The 4A and the 4B order options for a digital I/O module found in a universal relay Multilin also have four MOSFET outputs. The difference between the three order codes is that the 4A option lacks monitoring capabilities, whereas the 4B order option can monitor voltage with optional current monitoring. As specified earlier, the 4C order option can monitor current with the additional option to monitor voltage depending on the specific unit. Other digital I/O modules may be of a different characteristic entirely (form-A or form-C) or contain RTD inputs for temperature monitoring features. The digital I/O contained in the UR is specific to the end function and application of that universal Multilin relay.