A method of adding a power feed to electrical systems includes coupling a set of input lines to a power source such that the input lines are connected to at least one phase of AC power from the power source, and coupling a set of backfeed lines to an output receptacle in a power distribution unit. The output receptacle may be connected in parallel with at least one other output receptacle that is supplying primary power to systems in the data center. The set of backfeed lines and the set of input lines may be tested to determine a match between a pair of lines in the set of backfeed lines and a pair of lines in the set of input lines. Determining the match may include matching the phase of the pair of backfeed lines with the phase of the pair of input lines.