a standard voltage for homes in the united states is 110 v
Following voltage harmonisation, electricity supplies within the European Union are now nominally 230 V ±10% at 50 Hz. For a transition period (1995--2008), countries that had previously used 220 V changed to a narrower asymmetric tolerance range of 230 V +6%/−10% and those (like the UK) that had previously used 240 V changed to 230 V +10%/−6%. No change in voltage is required by either system as both 220 V and 240 V fall within the lower 230 V tolerance bands (230 V ±10%). Some areas of the UK still have 250 volts for legacy reasons, but these also fall within the 10% tolerance band of 230 volts. In practice, this allows countries to continue to supply the same voltage (220 or 240 V), at least until existing supply transformers are replaced. Equipment (with the exception of filament bulbs) used in these countries is designed to accept any voltage within the specified range. In the United States and Canada, national standards specify that the nominal voltage at the source should be 120 V and allow a range of 114 V to 126 V (RMS) (−5% to +5%). Historically 110 V, 115 V and 117 V have been used at different times and places in North America. Mains power is sometimes spoken of as 110 V; however, 120 V is the nominal voltage.
Mains electricity