Yes, UK and USA mains plugs/sockets are different. The UK socket has shutters over the live and neutral openings and the shutters will only open when the earth pin of a plug (which is longer than the other two pins) is pushed into the socket. In the UK, all plugs have to have an earth pin or else the shutters won't open. Often the earth pin isn't actually connected to anything and is made of plastic.@rothwellaudio: maybe this will help....
AC plug on UK wall wart for P3 ..... Rule Britannia
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North American AC outlet
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North American supplied wall wart for P3
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Anyway, a tonearm doesn't have to be connected to mains earth to shield the tonearm wires. It has to be connected to the earth pin on the phonostage (which doesn't have to be connected to mains earth either).