Luke
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Also bearing in mind most of Europe is 110v, so 55v each way, so not too bad, whereas the UK is 240v, so 120v each way, which at 13A can kill you...
There's no 'each way' as above with mains voltage. 230V AC is the RMS voltage. The sine wave peaks at 325V and -325V.
Site 110V transformers are centre tapped, so in that specific case, 110V is actually two windings that give 110V across them, but only 55V to earth, so reducing the short-to-earth (and maybe through a person) voltage. That's still RMS so still peaks at 78V but crucially is also 0V 100 times a second (the same as any other 50Hz supply).
A lot less than 13A will kill you, if it gets to your heart. A few hundred mA will do the trick. That's why RCDs trip at 30mA.
Lower voltage is safer because low voltages can't break down insulation (in this case, your skin). As the voltage rises, it can break down more insulation. At thousands of volts, the air itself has trouble holding up as an insulator, which is why power cables on pylons etc. are kept apart.