High impedance differential relays protecting power system busbars is a favoured practice in many utilities. Simplicity and continuity with tried and trusted practices are key for this solution. A modern numerical (digital signal processor-based) protection relay offers a number of advantages compared to the more conventional electromechanical schemes. This paper describes the principles of high impedance differential busbar protection and buswire supervision and the associated auxiliary relays used to complete conventional schemes such as zone In/Out switches, zone indication relays, DC supply supervision etc. The paper also describes how a numerical relay can be customised to replace many of the auxiliary relays associated with conventional high impedance busbar schemes using the function keys, programmable tri-colour LEDs, editable user alarms and powerful programmable scheme logic (PSL). In addition, marshalling of trip commands to the correct circuit breakers connected to a faulted bus zone can be achieved dynamically, adapting to the switching status of disconnectors, with the PSL. The paper also describes how the CT requirements are determined via test using a Real Time Digital Simulator (RTDS).