In electricity distribution systems with weakly meshed structure and radial operation, the determination of the optimal radial configuration for a given objective function (e.g., minimum losses) is a challenging task because of lack of regularity of the system topology. This paper provides benchmark results on the determination of the configuration with minimum losses for five test networks commonly used in the literature. The analysis is carried out for a single set of data representing the system loading. Further results considering a multiple reconfigurations run at successive time intervals are included in the companion paper (Part 2).