In the US and Canada, 220, 230, 240 and 250 volts are used interchangeably to describe one voltage range that is used to power larger appliances. Similarly, 110, 115, 120 and 125 volts all refer to the one voltage range that is available through the common electrical outlet. The sources of these seemingly different numbers are as follows:
1. The 220 volt and 110 volt designations are older and familiar terminology, but are no longer used in either product design or by electric utilities in the US and Canada.
2. The 230 volt and 115 volt terminology comes from equipment design standards. Equipment is commonly designed to operate at 230 or 115 volts plus or minus 10%.
3. Electric utilities typically deliver electricity, under standard conditions, at 240 volts and 120 volts plus or minus 5% at the transformer.
4. The 250 volt and 125 volt terminology is from outlet, plug and switch design standards. The switches and outlets that we encounter in buildings, and the plugs that are on the power cords of our appliances are rated for the top end of their voltage range. Thus one will find they are marked 250 or 125 volts.
When one takes into account that equipment is designed to accept voltage variations of 10% at a minimum and that the electric utility regularly delivers electricity within 5% of their standard, there is a good match between the voltage the electric utility delivers and the voltage equipment was designed to use.