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Three pins, three different jobs

What Is Happening Inside a Plug?

A plug has more than one pin because electricity needs a way in, a way back, and a way to escape if something goes wrong.

One pin carries thepush inOne carries it back outOne is an escape routeto the groundA fuse cuts the lot ifit goes wrong
Three pins, and none of them is spare.

  1. Step 1 of 5

    Electricity has to go round, not just in.

    Out of the socket Through theappliance Back into the socket Round andround, fiftytimes a second

    It only flows if there is a complete loop. One pin brings the push in and the other takes it back out, so a single pin could never work no matter how thick it was.

  2. Step 2 of 5

    The third pin is only for accidents.

    Normally The earth pin carriesnothingIf a wire comes loose It takes theelectricity, not you

    The earth pin is connected to the metal case and to the ground, and normally carries nothing. If a loose wire touches the case, the electricity rushes down it instead of through you.

  3. Step 3 of 5

    A fuse is a wire designed to fail.

    1 A deliberatelythin wire2 Too muchcurrent heatsit3 It melts andthe circuitbreaks

    Inside the plug is a thin wire that melts if too much electricity flows. It breaks the circuit in a fraction of a second — sacrificing itself before the cable can catch fire.

  4. Step 4 of 5

    The design keeps fingers out.

    An ordinary wallsocket Shutters that only theearth pin opens

    Sockets have shutters that only open when the longer earth pin goes in first. Plug pins are sleeved in plastic near the base, so a half-pulled plug has nothing live to touch.

  5. Step 5 of 5

    Countries chose different shapes on purpose.

    An adapter Changes the shape onlyA converter Actually changes thevoltage

    Pin shapes and voltages were settled separately by different countries decades ago and never converged. An adapter changes the shape; it does not change the voltage, which is why some things still burn out.

    The earth pin is longer than the others so it connects first and disconnects last — the safety is in place before anything is live.

The short version

A plug's pins give electricity a way in, a way back and an emergency escape to the ground, with a fuse that fails on purpose.

Try it yourself

Look at a plug's pins. The bottom half of two of them is black plastic — that is so a half-pulled plug has nothing live to touch.

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