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What are the differences between 220VAC, 230VAC and 240VAC Mains Supplies and what voltage equipment should I use?

For many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.
Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.
Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage  to 240VAC + 6% and - 10% and European to 220VAC +10% and -6%  (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!
Depending on the voltage sensitivity of the product and the variance from nominal of the actual supplied voltage, it may not be advisable to use a 220VAC specific device in the UK or a 240VAC specific device in Mainland Europe etc. For instance a 240VAC supply can rise to as high as 254.4VAC and still be within tolerance, but the maximum rated voltage for a 220VAC product is only 242VAC. A 220VAC supply can drop as low as 206.8 within tolerance but the minimum rated voltage for correct operation of a 240VAC product is 216VAC It may work perfectly well either way but it could be, technically, outside the specification of the equipment with obvious implications. A 230VAC product must be compatible with all voltages across this range
If a product is to be used in the UK a 240VAC rated device is ideal but either 240VAC or 230VAC products can be used with confidence.
If a product is to be used in mainland Europe or Irish Republic a 220VAC rated device is ideal but either 220VAC or 230VAC products can be used with confidence.
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