Understanding basic electricity?

Discussion in 'A+' started by mikehende, May 20, 2006.

  1. JonnyMX

    JonnyMX Petabyte Poster

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    Sure, if someone would like to clarify exactly it is.
    As I understand it so far, the basic flow is power through the live wire, with neutral for any overspill and earth for accidents...

    Is that a reasonable summary?
     
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  2. phoenix510

    phoenix510 Byte Poster

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    Also chaps I would also say that with new regulations coming ref electricity in the house if you have changed light sockets and wall sockets and they are not inline with the age of the house ( fancy chrome fittings in a period house ) then you will need a certificate signed by a qualified electrician before you can sell the house.
     
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  3. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    See "Part P" of the "Building Regs". :eek:

    Harry.
     
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  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Correcting my earlier post - the most common outlet with only two pins is the shaver socket!

    These days these are covered with cautionary stickers (well - in hotels anyway). I note that my razor has the double box, denoting a doubly insulated device.

    This is somewhat of a special case. AFAIK normal outlets should include an earth.

    Harry.
     
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  5. mikehende

    mikehende Kilobyte Poster

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    Look at this Johnny, if this turns out to be correct then can you redo the image using the black line or whatever you wish as the electricity flow please? ok guys, concerning the "flow" of elcetricity, can you guys take a look at the diagram please and tell me if this is how the electricity flows in from the street and out again? In particular, looking at the wall AC outlet, is that the path of the electricity, to flow from the Live slot through and to the Neutral slot then back out through the Neutral wire? Thanks.
     

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  6. JonnyMX

    JonnyMX Petabyte Poster

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    Will do.
     
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  7. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    The "binded together" part of your statement should not be in there, as it is wrong and misleading!

    The fact is that *generally* you can touch a neutral or earth wire and not get a shock even if you are standing with wet feet on a conductive surface. As Harry has said, this is because both neutral and earth, should be at zero potential. You can also touch the live wire and not get a shock *if* there is no path for the current to flow i.e. you are not in contact with the neutral wire and or you are not creating a path to earth.

    Electricity will only ever flow if there is a circuit. A circuit is a path back to the source. If you touch a live wire with your right hand and touch the neutral or earth wire with your left hand, you will create a path for current to flow right across your chest. This is one of the most dangerous shocks you could receive because the current passes through your heart.

    It is also worth mentioning that with house lighting wiring neutral coloured wires may actually be live, this is often the case with wall switches and it is done to minimise the amount of cable needed. Hence, as Harry has also stated and I totally agree with, always isolate the circuit you are working on by removing the fuse or switching off the circuit breaker or sooner or later you will get got.
     
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  8. mikehende

    mikehende Kilobyte Poster

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    Yes, that was a mistake, using the words "binded together", what I had meant was what you wrote, touching both N and L wires at the same time thereby creating a path for the current to flow, also, this is a very nice explanation Bluerinse! :D

    So now we're making progress, on to the next step. If someone takes a screwdriver and places it into any of the 2 slots in a wall AC receptacle, he/she is supposed to get shocked, correct? If so, why does using a tester or Neon light screwdriver or wearing rubber boots prevent this from happening?
     
  9. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Depends on the screwdriver and the slot it is put into.

    An electrical screwdriver will be insulated, so not a lot will happen with either slot. The point here is insulation. This stops current flowing. This is why mains cable has an insulated wrapping, so anybody touching it, even when it is on, won't get a shock. Rubber boots will probably be an insulator - thus being somewhat items of safety-wear.

    The neon screwdriver mentioned earlier isn't a perfect insulator, but allows a very tiny current to flow. This is too small to cause an electric shock, but enough to light up the neon.

    It is all about whether an electric circuit is allowed to happen, and how much resistance is put up to stop it happening.

    Harry.
     
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  10. mikehende

    mikehende Kilobyte Poster

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    The special screwdrivers with the insulation I understand will prevent you from getting shocked but the rubber boots I don't understand especially since the boots are at the bottom of your body, if it's the boots that preventing you from getting schocked, then the current has to pass through your arms and through your body before it gets all the way down to the boots so why wouldn't you feel the current as it passes through your body?
     
  11. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Because the circuit has to be complete for any current to flow.

    No current will flow unless this is the case.

    (I'm ignoring static electricity here)

    Forgive me - but after 50 messages in this thread it appears to me that you still haven't grasped how electricity works. I suspect the medium is the problem - different people respond well to different learning situations. Perhaps - for your own safety :biggrin - you need to do a short course on this at your local adult education place, or do a fortnight apprenticeship with a good electrician. Your life might depend on it!

    Please don't take the preceeding the wrong way - it is just that your questions seem to imply that the idea of an electric circuit just hasn't 'clicked' with you yet.

    Harry.
     
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  12. mikehende

    mikehende Kilobyte Poster

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    Yes, I am having an extremely hard time with this which is why I need for someone to explain this via either a diagram or animation which was/is the purpose of this thread but I can't find anyone [yet] who can explain it using this method, will keep on trying though and when I get it, I will show it here, I am closing in on it though, first step is to get someone to confirm/deny the flow in the diagram.
     
  13. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    To be honest, the diagram is somewhat confusing, and if it is confusing to me, a qualified radio, TV and electronics engineer, then I am certain it will be confusing for you.

    Try this..

    Live (240V AC)--------------load---------------Neutral (O volts)


    Focus on the live and neutral and forget earth for the moment.

    Current will flow if there is a potential difference on either side of the load (the load could be a bulb for example). On one side of the load, you have 240V on the other side you have 0V. It is that potential difference that causes current to flow.

    If the potential is the same on either side of a load, current will not flow. That is why birds can stand on electricity power lines without getting fried, because their feet are both at the same potential.

    Okay, now earth is another route back to the source. The power station is earthed and so electricity can flow through the ground and complete the circuit. Things would still work without an earth wire but is is incorporated in most things purely for safety reasons.
     
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  14. Celia

    Celia Bit Poster

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    I think the closest analogy to the ground cable is the overflow outlet on your bath/sink.

    I think you will also find electricity easier to understand if you work through this interactive revision guide.

    http://www.gcse.com/electricity.htm

    If you go through it in order you'll have a better understanding of the basic concepts and how it works.
     
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  15. Malnomates

    Malnomates Megabyte Poster

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    Nicely put Celia.. 8)

    Another example to put things in perspective with regards to voltage and current (the actual flow of electrons) is static electricity.

    We know that when we recieve a static shock the voltage is going to be above 3500 volts,read it again....3500 volts :eek: .In most cases a static discharge will peak well above that,somewhere around the 10kv mark... :ohmy ...but the current (flow) is very,very low,so all we get is a slight *ZAP* and spiky hair!

    However,should the current be raised,we would find ourselves in a rather uncomfortable situation and in this case (we are talking about thousands of volts and a significant current this time) we would be in dager of serious injury,or worse.

    Anyway,the point of this little exercise is this little ditty that my mentor,many moons ago taught me....."It's not the voltage that kills you...It's the current!"
     
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  16. mikehende

    mikehende Kilobyte Poster

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    I was told the exact same thing by a friend of mine who is also an Electronics Technician, he questions why you have "2" lines and 2 neutral wires coming into the house?

    @Celia, that is a nice link [thanks] but I think I may have found something more graphic last night that might bring me closer, will work on it today and get back to you guys here later.

    @Harry, stay with me, almost there!
     
  17. mikehende

    mikehende Kilobyte Poster

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  18. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    That's pretty good! I had done some searching for similar material, but the things I found didn't quite click for what I felt was needed.

    Harry.
     
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  19. mikehende

    mikehende Kilobyte Poster

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    Well, from that animation, now I get the "circuit" concept you and others were trying to explain to me all this time. I have done the reasearch on the Power Grid, from the plant to the home to the outlet and now from this link I am much more knowledgeable now than before where electricity is concerned, as an example, I would always wire multiple tweeters in parallel and Series but never knew exactly "why", just followed what I saw others doing, now I know the difference between the 2 methods and why but to be honest I am still after another diagram to clear up a few things still eating away at me so my work with this is not complete, unfortunately.
     
  20. twizzle

    twizzle Gigabyte Poster

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    Ok now im gettin a lil confused here and im sposed to be a spark!!

    What you want to know is how do we get a electric supply into a house? How does it flow and where from/to? Or do you want to know more? All this is far more indepth than the A+ requires but i can see that some knowledge would be helpful in some situ's.

    Taking the basic supply to a house, you have 3 wires into your main domestic fuse box/meter distbox.
    Live. Neutral and Earth.
    Live is normally red or brown, Neutral is Blue or Black and Earth is Yellow and Green (not Yellow on its own as thats a phase color) This depends on how old the house is etc (older houses have red and black, newer regs state that Brown and blue are used)

    If you put a volt meter between Live and Neutral you get 240VAC (in the UK), Between Live and Earth you get 240VAC and between Eartha nd Neutral you get 0Vac.

    Now the reason there is a neutral as far as i can say is that ther Earth is used as a safety circuit to ground (which can be a metal spike outside your house) And the neutral completes a live circuit back to the power station from the live wire alowing the current to flow. (btw covention states is flows from + to - but actually if flows from - to +). The Neutral creates a slightly different potential between it and the live compared to the earth and live. Its not much but there is a difference and its this that makes the circuit usable. (You cant use a circuit that goes direct from live to earth as the voltage is grounded directly with almost no potential.)

    The neutral wire is, however grounded to earth at the power station end if i recall right. As far as i can suggest its only used to complete the circuit so that a 3rd wire (Earth) can be used as a saftey measure. For example, in an appliance 3 wires go in, Live Neutral and Earth. The Live and neutral provide the circuit voltage to the appliance be it a monitor, iron, or Electric fire. The Earth wire is normally connected to the case of the appliance or some metal contact that all the earths in the appliance run to. Now if the live wire breaks in the appliance the ciruit is broken so the appliance fails to work, (now flow back to neutral) However if that wire touches the appliance case theres a potential for a ciruit to be completed via you touhing it, to the ground. So you get a shock. But due to the erath wire being connected to the case the cuircuit is now remade back to ground at the earth spike outside your house, so with luck you do not get a shock.
    If its the neutral wire that breaks in the appliance then the circuit is still broken, but as this has a potential of almost 0v, not current/voltage is flowing down it. However in an AC circuit this isnt true as the current is switching back and forth form live to neutral at 50hz so it carries some voltgage which again needs to be pulled down to ground via tha earth wire.
    In double insulated appliance an Earth wire is not needed as there should be now way for the Live to complete its circuit down to earth via someone touching a case. These appliances are onew with only 2 wires in the plug normally (like your electric shaver and hifi) However they can have all 3 wires in the plug but the Earth wont be used inside the appliance. The Neutral wire is always used however to complete the Mains circuit.


    All this changes again if you take into considersation that 3 phasesare used to supply a complete town. RED BLUE and YELLOW are the colors used and if measrued between each you get 240vac, EG RED to BLUE, BLUE to YELLOW and RED to YELLOW all gives you 240vac. However measure all 3 phase and you get 415vac. Each phase is used to supply different streets ina town so there is little chance of an overload on one killing power to all the town.
    Also different countries use different supply voltages. The UK and most of europe use 240Vac (tho some use it at 50hz and others at 60hz i think), The US has 110vAc at 60Hz and i have been told that the different islands of Japan can use widley differing voltages to each other!! And a 240Vac device cannot work ona 110Vac supply and vice versa (tho plugging a 110Vac appliance into a 240Vac supply can give a bigger bang!!)

    Also ina DC circuit there is no neutral as asuch. This normally becomes the 0V rail which can be tied down to earth within the circuit itself otehr wise it can cause a floating voltage jsut above 0v dc wich can cause signal problems. And all screened cables have thier screens tied to earth at one end to reduce the signal to noise ratio.

    Now all this is outside of the remit of A+ and porbably a load of old nonsense i have spouted, and its sure confused the hell outta me.

    Just remeber Live and Neutral are needed for a AC circuit to work correctly (think of a sine wave with the upper peak the live and the lower peaks the neutral) and the earth is used for saftey only,it should never carry any voltage unless a fault develops. (neutral carries voltages sometimes). Without adequate diagrams and training its hard to get across and explain.. I just know what im doin when i make a circuit whether its on a pcb or changing the House wiring.

    (as an aside, from what i have been led to belive you do not need a cert from a qulaified electrician if you only make a minor mod to existing house wiring. Installing a new ring main needs a qualified electricains cert and an inspection form the local council while adding a spur to and existing ring dosent.)

    End of long boring usless post.. Have fun!!
     
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