Systems and methods testing a power protection relay include a merging unit to receive signals from an electric power delivery system. The merging unit includes a test signal input to receive test signals from a testing device, a relay output to output at least one of the test signals to a power protection relay, a distribution output to output at least another of the test signals to one or more additional merging units, and a switch subsystem to route the test signal to the relay output or the distribution output.