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Wiring of electrical plugs question

Discussion in 'Science' started by gainly, Jan 14, 2020.

  1. gainly

    gainly Lead commenter

    When teaching wiring of plugs, I have often wondered why the UK is almost the only country which has a fuse in the plug and an earth wire. Does anyone know why? Do other countries have additional safety features elsewhere in the circuit or is the UK just more safety conscious?
     
  2. Rott Weiler

    Rott Weiler Star commenter Forum guide

    Don't know the answer to the specific question but UK-style plugs aren't only used in the UK. Quite a lot of countries use them - Ireland, Singapore, for example - full lists can be found online - generally countries which were once UK colonies.
     
  3. Stiltskin

    Stiltskin Star commenter

    Its implementation was a consequence of copper shortage during ww2 and the need to use ring circuits.
     
    EBC likes this.
  4. gainly

    gainly Lead commenter

    Thank you, so do countries where there is no fuse and earth wire in the plug not use ring circuits?
     
  5. neddyfonk

    neddyfonk Lead commenter

    Implemented correctly, a plug with the correct amperage fuse helps to identify faulty equipment and isolate it before it starts a fire or hurts someone without blowing the fuse in the mains distribution box. Nowadays RCDs ( Residual Current Detectors) are a far safer option because they can react to transient events (sparks) far quicker but sometimes the 'event' is impossible to track down as the causal factor. It took scientists years to establish some computer systems failed because solder under stress on PCBS (printed circuit boards) can grow lead 'whiskers' that can cause tiny short circuits.
     
  6. Stiltskin

    Stiltskin Star commenter

    No, they use a radial system mostly. They still have an earth though (it's the notch at the top in German plugs or a hole in the middle on French plugs).
     
    gainly likes this.
  7. gainly

    gainly Lead commenter

    Thank you, very helpful. Since most of my students have visited either Europe or USA they sometimes ask about this.
     
  8. phlogiston

    phlogiston Star commenter

    When I had a mishap with my hedge clippers it was the old fashioned fuse in the plug that cut the circuit, with the rcd unaffected.
     
  9. alanbarnard

    alanbarnard New commenter

    The RCD has gone on and off the syllabus over the years. Its purpose is to detect current that is unintentionally flowing to earth (typically: appliance - right hand - heart - left hand - earth) as such it needs to disconnect the supply very quickly at very low currents (10's of milliseconds @ 10's of milliamps). It does not provide any protection against a fault causing excess current that does not does not flow to earth. Thus, in the case of phlogiston's hedge clippers, they are probably double-insulated and the mishap was presumably the blades cutting through the two-core cable thus shorting the conductors, the excess current blew the fuse but, as there was no path to earth, the RCD did not trip.

    I attach a few files that might be of interest/useful.
     

    Attached Files:

  10. blazer

    blazer Star commenter

    Thanks for that explanation. Father in law bought a batch of dodgy bulbs the other week. Fuse blew everytime we changed the bulb but RCD didn't trip. He took the remaining bulbs back to the shop where the shopkeeper didn't believe him when he said they were faulty. Shopkeeper put one in his display and blew the whole section of lights:D
     

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