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For large appliances I usually see a 3-prong plug while smaller electronics will use a 2 prong wall wart with a DC barrel. When designing electronics, how do you know if you'll need an earth ground? Are the two prong designs inherently more dangerous?

cspirou
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    Devices using just live and neutral are often (always?) double insulated meaning that any high voltage stuff is insulated within the case the electronics are in. – John Hunt Jun 16 '15 at 09:48

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The regulations are described here: https://en.wikipedia.org/wiki/Appliance_classes . Actual implementation varies by country - all UK sockets have 3 pins for example.

Small appliances can use low-current low-voltage DC. All the safety isolation is in the wall wart; it's not possible for the appliance itself to fail in a way that gives the user an electric shock.

Larger appliances either have a power supply built in or use mains directly (drills, white goods, lamps, etc). These must either be double-insulated or have an earth ground.

pjc50
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