From APPX 2 IEE regs:
In November 1988 the European electrical standards body CENELEC agreed on harmonization of "low voltage" electricity supplies in Europe......
The measure is intended to harmonize mains electricity supplies at 230v within Europe. CENELEC has proposed three stages of harmonization, the first two stages of which are shown below:
Effective date, V Nom, Permitted tol, Permitted voltage range.
Pre 1995, 240V +6%/-6%, 225.6 - 254.4V
1 Jan 1995, 230V +10%/-6% 216.2, - 253V
1 Jan 2008 (Proposed), 230v +10%/-10%, 207 - 253V