Tripp Lite PDUs accept either "Single-Phase" or "3-Phase" input voltage. What does "Phase" refer to? Power moves along a transmission line in the form of a wave. Each of the "waveforms" is called a "Phase". For efficiency's sake, utility companies deliver three waveforms (or 3 phases) on the same transmission line from the generator to a facility. Also for efficiency's sake, a facility's electrical panel will deliver 3-phase power along some circuits to high wattage loads. For lower wattage loads, the panel will split the power into single-phases delivered on separate circuits to separate sets of devices. The phase and voltage of the PDU must match the phase and voltage of the outlet it is plugged into. Single-Phase PDUs plug into a single-phase source and deliver single-phase power to connected devices. Single-Phase PDUs are offered in a variety of configurations, including Basic, Metered, Monitored and Switched.