Proper grounding and isolation techniques are highly effective in protecting signal integrity from natural and industrial hazards. Although the National Electrical Code requires grounding systems and does not allow load currents in ground lines, ground currents often exist, causing voltage drops and instrumentation errors. This white paper summarizes typical power distribution topologies, examines a typical voltage distribution panel to indicate how voltages are distributed and where ground connections are made, and provides several examples of situations that can arise regarding unexpected voltages on ground lines.