North American Voltage Ranges
In the United States and Canada, the electrical power supplied to most homes is a split-phase system. That power enters your home at about 240 volts. This 240 volts is split at the main circuit breaker panel into two 120 volt halves, called phases. The 120 volt level is commonly referred to as 110, 115, 120, or 125 volts and is used for lighting and ordinary outlets. Similarly, 220, 230, 240, and 250 volts are used to describe the higher 240 volt level. This higher voltage range supplies larger appliances such as clothes dryers, large air conditioners, and electric vehicle charging. But why all the different numbers?
120 and 240 Volts
1. The electricity delivered to your home by the electric utility is at 120 and 240 volts. This is called "nominal voltage." This is the voltage as measured at the utility transformer outside your home. Nominal voltage will vary about plus or minus 5 percent under ideal conditions.
110 and 220 Volts
2. "110 volts" and "220 volts" represent an older standard that was changed to 120 and 240 volts about 75 years ago, depending on the region. This terminology is still familiar to many people and remains in use.
115 and 230 Volts
3. "115 volt" and "230 volt" come from product designers. These voltages are slightly lower than the 120/240 volt utility voltage to compensate for voltage loss over the wires from the utility transformer.
125 and 250 Volts
4. Outlets, light fixtures, and switches are rated at 125 or 250 volts, a higher voltage that might encountered on the electrical circuit.
5. “208 volts” is usually found in commercial and industrial electrical systems which are supplied with 3 phase electrical power. In the most common 3 phase systems, there are three sources of 120 volts for common outlets and 208 volts for larger appliances. Quick 220® Systems will deliver 208 volts when plugged into two 120 volt phases of a 3 phase electrical system. The math and layout of 3 phase systems is complex. However, if you want to know more, Wikipedia.com is a good place to start.