Types of Voltage

There are two voltage types: direct current and alternating current. Direct current flows in one direction. Alternating current flows in one direction, then switches directions.

208 Volts

208 volts is the amount in three-phase power systems. There are two 120 V(AC) power sources and resistance sources ran in series in these systems. The amount of voltage between each power source and resistance is 207.85 V(AC), which is rounded up to 208.

Uses

A 208 V(AC) system is safer and more efficient than other types of systems because the same current is pulled as with a single, higher voltage circuit. The overall voltage used in three-phase power systems is 32 volts less than in single-phase power systems.

Considerations

Since most 208 V(AC) systems are for commercial buildings, products that require that voltage aren't compatible for residential use. If you are purchasing electrical appliances for your home, make sure they are compatible with your voltage sources.

Warning

To prevent electric shock when measuring the voltage output in a circuit, make sure you do not touch any "live" areas with your skin. Make sure that your measurement tools are properly insulated as well.

Source:

All About Circuits: Three-Phase Power Systems

Physics Forums: AC and DC Differences

Behlman Electronics: AC Power Source Configurations