Understanding AC Current for Beginners

[PainterGuy]

hello everyone,

this is diagram from a book:-
http://img816.imageshack.us/img816/4671/clipperac.jpg

this is same diagram i have modified:-
http://img849.imageshack.us/img849/1848/modifiedclipperac.jpg

this is truth i don't understand how AC current work. let me tell you what i think of AC. as in my modified diagram you see there are two terminals A and B. e^(-) stand for electrons and arrows stand for their direction of motion. when electrons are moving toward left of page current or voltage is +ve. and when electrons are moving towards right of page current is -ve.

i think each terminal, A and B, switches between +ve and -ve. when A is +ve, B is -ve. if frequency of AC is 50hz then each terminal switches between opposite polarities 50 times. it is all about push and pull of electrons.

i need only basic understanding of AC without math formulas. so don't puzzle me, please.

i am very much grateful for any help you can give me. many thanks.

cheers

 

[tiny-tim]

hello painterguy!

i think each terminal, A and B, switches between +ve and -ve. when A is +ve, B is -ve. if frequency of AC is 50hz then each terminal switches between opposite polarities 50 times. it is all about push and pull of electrons.

yes that's correct …

what's worrying you about that? ​

 

[PainterGuy]

hello painterguy!


yes that's correct …

what's worrying you about that? ​

hi tinytim,

so this means this is truth i understand what ac is! correct, am i?

perhaps i was confused... may i ask you something? do you really like fish? i can gift you some!

cheers

 

[PainterGuy]

hi everyone,

i was reading that live wire is coloured brown, neutral blue and Earth green/yellow.

in AC both wires, live and neutral, carry voltage. then why is called "neutral"? it can cause equal damage as "live". catching any of the wires can hurt you.

in case of DC supply, suppose a battery, one should be in contact of both terminals of battery to get a shock because of internal chemical reactions going on inside the battery. is this right? now suppose we have a highly +ive charged van de graff generator, i think touch it would give one a shock for a second or two. is this right?

many thanks for any help you can give me.

cheers

 

[vk6kro]

Colours of electrical wires vary around the world. Yours is very common for 240 volt systems. We use the same one.

The neutral does carry current, but it is connected to ground for safety reasons outside your house. So it is not dangerous to touch it, although you should not do this. If you get it wrong, you may die.

If you touch both wires ( the active and the neutral) or touch the active while you are grounded, you will get a bad shock and you may die.

You can also get permanent injury and may have a faulty heart or paralysis for the rest of your life.

 

[b.shahvir]

i think each terminal, A and B, switches between +ve and -ve. when A is +ve, B is -ve. if frequency of AC is 50hz then each terminal switches between opposite polarities 50 times. it is all about push and pull of electrons.

Actually it is 100 times per sec... 50Hz is full cycle, the switching happens every half cycle from +ve to -ve, i.e 100 times per sec for 50Hz frequency.

 

[PainterGuy]

many thanks for helping me in an easy way.

Colours of electrical wires vary around the world. Yours is very common for 240 volt systems. We use the same one.

yes, it is 240 volt system.

The neutral does carry current, but it is connected to ground for safety reasons outside your house. So it is not dangerous to touch it, although you should not do this. If you get it wrong, you may die.

unfortunately this is not done where i live. but i was thinking how this achieved. like when someone touches the neutral wire (which also carry current just like live wire) then current will not flow through my body to ground instead it will start flowing through "earth" wire into the ground somewhere outside the home etc. okay. a human body has also resistance. so there are two choice for current either flow through Earth wire into the ground, or through the human body into the group. the first option of least resistance will be preferred.

normally live and neutral wires complete the circuit. both need each other. but when someone touches the neutral wire a huge current will tend to flow. so there would be some mechanism in the circuit that in such a case current instead start flowing into the Earth wire. is it so?

i was wondering why don't they also ground the live wire too? so that touching any of the wires is not injurious.

will you please comment on this:

in case of DC supply, suppose a battery, one should be in contact of both terminals of battery to get a shock because of internal chemical reactions going on inside the battery. is this right? now suppose we have a highly +ive charged van de graff generator, i think touch it would give one a shock for a second or two. is this right?

many thanks for this help.

Actually it is 100 times per sec... 50Hz is full cycle, the switching happens every half cycle from +ve to -ve, i.e 100 times per sec for 50Hz frequency.

yes, i think it is correct. thanks for correcting this.

cheers

 

[Averagesupernova]

many thanks for helping me in an easy way.



yes, it is 240 volt system.



unfortunately this is not done where i live. but i was thinking how this achieved. like when someone touches the neutral wire (which also carry current just like live wire) then current will not flow through my body to ground instead it will start flowing through "earth" wire into the ground somewhere outside the home etc. okay. a human body has also resistance. so there are two choice for current either flow through Earth wire into the ground, or through the human body into the group. the first option of least resistance will be preferred.

normally live and neutral wires complete the circuit. both need each other. but when someone touches the neutral wire a huge current will tend to flow. so there would be some mechanism in the circuit that in such a case current instead start flowing into the Earth wire. is it so?

i was wondering why don't they also ground the live wire too? so that touching any of the wires is not injurious.will you please comment on this:


many thanks for this help.




yes, i think it is correct. thanks for correcting this.

cheers

I think you have a few misconceptions. The fact that a wire is carrying current does not guarantee you a shock. I get the feeling that you think this, but maybe I'm wrong. What gives you a shock is when the wire you are touching and the ground you are standing on has a significant voltage between them. A neutral wire that is grounded could be carrying 20 amperes but there is no voltage between it and ground since they are connected together physically; there is no voltage between neutral and ground.
-
Now for the part I italicized: Draw a circuit diagram of what you proposed and tell us what you think would happen.

 

[PainterGuy]

I think you have a few misconceptions. The fact that a wire is carrying current does not guarantee you a shock.

hello Averagesupernova,

i think i understand it a a little bit. big current does not guarantee you shock. think of big water tank which is full of water but is on ground. it has very little potential to do any work.

i read somewhere that the machine which is used to weld metals carry high current but there is little voltage involved.

hope i have it correct.

What gives you a shock is when the wire you are touching and the ground you are standing on has a significant voltage between them. A neutral wire that is grounded could be carrying 20 amperes but there is no voltage between it and ground since they are connected together physically; there is no voltage between neutral and ground.

please see this picture:
http://www.siongboon.com/projects/2009-06-27%20230Vac%20electricity/3%20pin%20plug.gif

i was told once that the ground wire is connected to the body of an appliance. suppose the appliance is a fridge. somehow the fridge's body start conductive - i mean anyone of wires, live or neutral, makes direct contact with metallic body of fridge. in such a case the body of fridge is already connected to ground wire which goes into the ground outside the home. so even if i connect the fridge i will not get a shock because current has a easy alternative path. this is all i know about neutral, live, and ground wires so far.

please now lead me to correct path.

cheers

 

[b.shahvir]

Kindly study these earthing schemes;

http://www.electrical-installation.org/wiki/Definition_of_standardised_earthing_schemes"

Hope this helps!

Regards,
Shahvir

 

[PainterGuy]

hello Averagesupernova,

i think i understand it a a little bit. big current does not guarantee you shock. think of big water tank which is full of water but is on ground. it has very little potential to do any work.

i read somewhere that the machine which is used to weld metals carry high current but there is little voltage involved.

hope i have it correct.
please see this picture:
http://www.siongboon.com/projects/2009-06-27%20230Vac%20electricity/3%20pin%20plug.gif

i was told once that the ground wire is connected to the body of an appliance. suppose the appliance is a fridge. somehow the fridge's body start conductive - i mean anyone of wires, live or neutral, makes direct contact with metallic body of fridge. in such a case the body of fridge is already connected to ground wire which goes into the ground outside the home. so even if i connect the fridge i will not get a shock because current has a easy alternative path. this is all i know about neutral, live, and ground wires so far.

please now lead me to correct path.

cheers

Kindly study these earthing schemes;

http://www.electrical-installation.org/wiki/Definition_of_standardised_earthing_schemes"

Hope this helps!

Regards,
Shahvir

hi Shahvir,

every thing was over the head. someone please help me. banging my head against wall for last two days to understand this.

cheers

 

[b.shahvir]

Kindly mention in brief precisely what you are looking for...

 

[PainterGuy]

Colours of electrical wires vary around the world. Yours is very common for 240 volt systems. We use the same one.

The neutral does carry current, but it is connected to ground for safety reasons outside your house. So it is not dangerous to touch it, although you should not do this. If you get it wrong, you may die.

If you touch both wires ( the active and the neutral) or touch the active while you are grounded, you will get a bad shock and you may die.

You can also get permanent injury and may have a faulty heart or paralysis for the rest of your life.

Kindly mention in brief precisely what you are looking for...

hello everyone,

many thanks for reply. to understand where i am having difficulty you can start have a see on this thread from post#4 onward in this thread. the quoted post of vk6kro is post#5.

i do not understand how neutral is connected to ground. i think when male plug, say of an oven, in inserted into a female connector, circuit completes and oven starts functioning. both neutral and live carry voltage. unless connection establishes between them the oven will not work. now if already have connected neutral to ground wire then current out of the neutral wire will not flow through the oven instead will go to ground (earth) wire.

cheers

 

[b.shahvir]

hello everyone,

many thanks for reply. to understand where i am having difficulty you can start have a see on this thread from post#4 onward in this thread. the quoted post of vk6kro is post#5.

i do not understand how neutral is connected to ground. i think when male plug, say of an oven, in inserted into a female connector, circuit completes and oven starts functioning. both neutral and live carry voltage. unless connection establishes between them the oven will not work. now if already have connected neutral to ground wire then current out of the neutral wire will not flow through the oven instead will go to ground (earth) wire.

cheers

You have got the concept all wrong... any wire in any electrical system can be grounded with respect to the other conductor, provided the voltages between all the other live conductor/s and the grounded conductor are equal. This is true for AC (multiphase/multiwire) systems as well as DC (multiwire systems)

The conductor which is 'chosen' to be earthed (as mentioned above), is termed as 'Neutral conductor', as the voltage between the said Neutral conductor and Earth is 'zero'. However, there will be full voltage between the remaining 'Live' conductors and this 'Neutral' conductor. There will also be full voltage indicated between all the other available Live conductors and the Earth or Earth wire.

The connection of the chosen Neutral conductor to Earth is made at the Substation transformer/generator end. What is done is the 'Neutral' conductor is connected by a conducting strip to an 'Earth pit'. The electrical panel from whch the various electrical loads (such as oven, etc.) will now be fed has an 'Earth bus-bar' (conducting bar of Copper or Aluminium). This Earth Bus-bar is connected to the sub-station earthing strip. Now the Earth (yellow/green wire) connected to your Oven body is directly or indirectly connected to this panel Earth bus-bar through the electrical system network.

The Earthing wire is an extra safety wire (in parallel) with the Neutral wire depending on Earthing scheme (sometimes Neutral wire is also used as Earthing wire in electrical systems in some countries, there is no provision of separate Earthing wire). The separate Earth wire carries only FAULT current from the Oven body if at all accidentally the live conductor comes in contact with Oven body. At all other times the current thru Earth wire is 'zero'.

It is interesting to note that in normal condition there may be a residual voltage indicated between Neutral wire and Earth wire of say between 1 to 3 volts. This is due to voltage drop in Neutral wire and residual leakage currents which might flow in Earth wire under normal conditions, but they are harmless. You will never get a shock due to this residual voltage/currents between neutral and Earth, but these leakage voltage/currents are sometimes harmful for certain sophesticated digital equipments.

I suggest you study my link on Earthing schemes slowly and you will understand the logic. Do not rush thru the study... The Earthing scheme I've mentioned above is the TN-S earthing scheme for a typical 3 phase distribution system, in my link see Fig. E5. Here, 'PE' is the Earth wire which is connected seperately from Neutral wire at substation transformer end.

NOTE:- In 3 phase systems the middle wire (connected to the star point) is chosen as Neutral wire and is Earthed as the voltage between all the other remaining 3 Live wires and the middle wire (or Earth) will remain the same inspite of it being connected to Earth.

 

[sophiecentaur]

hello everyone,

many thanks for reply. to understand where i am having difficulty you can start have a see on this thread from post#4 onward in this thread. the quoted post of vk6kro is post#5.

i do not understand how neutral is connected to ground. i think when male plug, say of an oven, in inserted into a female connector, circuit completes and oven starts functioning. both neutral and live carry voltage. unless connection establishes between them the oven will not work. now if already have connected neutral to ground wire then current out of the neutral wire will not flow through the oven instead will go to ground (earth) wire.

cheers

A circuit which consists just of the generator and your cooker has current 'all the way round' because of the Potential Difference (Voltage) across the generator output. This is nothing to do with the presence of any ground connection; the system could easily 'float' (think about running such a system in an aeroplane - no ground to connect to?)

In a simple (single phase) system, either leg could be held at or near ground and it would prevent the voltage from floating upwards in an uncontrolled way. The highest voltage to ground you'd measure anywhere. would be 240V. The PD between Earth and Neutral is nominally zero but can be a few (safe) Volts. If you touch the Neutral, there is such a low voltage 'across you' that no detectable current flows through you. - no shock.

BTW current does NOT "take the easiest route". Elementary Teachers say this and they should be shot! The current is shared out, according the the resistance of each path. You are a high resistance and the Earth connection is a low resistance. Most of the current will flow down the Earth wire (which is why the Neutral voltage remains near Zero).

 

[tiny-tim]

… (think about running such a system in an aeroplane - no ground to connect to?)

hi sophiecentaur!

what are the regulations for earthing electrical equipment in an aeroplane?

 

[sophiecentaur]

Dunno. The options are to use a fully balanced / floating system or connect one (which you'd call the Neutral>) to a point on the body of the plane and call that Earth.

 

[b.shahvir]

The hull of the air-plane acts as virtual earth...

 

[sophiecentaur]

"Virtual Earth" has a rather more special, reserved meaning, I think, involving an OP Amp and current feedback. The term "Ground' might be a bit better in that context. There is plenty of electronic equipment with no Earth connection but which uses an internal connection to a chassis or ground plane.

 

[PainterGuy]

hello everyone,

many thanks to everyone for helping me out here. i hope this post will explain you where i have problem in my understanding so my request is that you read my post (check out the linked diagrams carefully). please. and please don't make it more complicate! i am going to use electron current concept below and concept of pushing of electrons because this makes things easy for me somewhat.

first have a see on this image:
1:-- http://img339.imageshack.us/img339/1278/stuckinac2.jpg

my commentary on the above image:
there are two terminals L and N. e^(-) stand for electrons ('electron' current) and arrows stand for their direction of motion. when electrons are moving toward left of page 'conventional' current or voltage is +ve. and when electrons are moving towards right of page 'conventional' current is -ve.

i think each terminal, L and N, switches between +ve and -ve. when A is +ve, B is -ve. if frequency of AC is 50hz then each terminal switches between opposite polarities 100 times. it is all about push and pull of electrons.

now come to this drawing:
2:-- http://img864.imageshack.us/img864/9137/stuckinac.jpg

my commentary (and all my confusions!) are there on the diagram. if you have difficulty deciphering my writing there please let me know i will make in clear.

please now take me out of this confusion. it has been days that this confusion is surrounding me.

cheers

 

[b.shahvir]

The N & G wires are connected at Transformer star point and brought out seperately at the recepticle. But let us assume as in your case that the N & G wires are connected locally at the recepticle by a conducting link. The G wire is actually connected to the body of the oven and is not clearly indicated in your 2nd diagram. In that case the G wire will not carry normal return current from heater, but only fault current if the live wire gets accidently connected to the body of the oven.

Coming back to your case, the return current from oven heater will now divide itself into 2 parts; one half will flow thru N wire and other half will flow thru G wire.This is because due to conducting link, the N & G wires become low resistances connected in parallel. Pls. note that the division of current will be directly proportional to the value of N & G wire resistances. If we assume that the resistance of G wire is 'zero' (practically impossible), then all of the return current from oven heater will flow thru G wire and not thru N wire. Now, if we assume the resistance of N wire to be 'zero' (again practically impossible), all of the return current from oven heater shall flow thru the N wire and not thru G wire.

So you see, current flow is relative to situation and depends on wire resistances & is not fixed. Your description of 1st diagram is correct but figure is incorrect. I think your understanding of electron current flow (AC/DC) is not clear. Try referring basics.

 

[sophiecentaur]

First. Stop using electrons in your discussions of normal circuit behaviour. You may think it works ok thus far but it will lead you up the garden path. Why do you think that the cogniscenti use Conventional Current? Do you think it's just to be flashy? If you are struggling then be prepared to take some advice in this respect.

In AC, the voltage of one wire alternates positive and negative RELATIVE to the other wire. It matters not if one of the wires it connected to somewhere else (it could just as well be connected to the + terminal of a 500V battery with the battery's other terminal connected to ground). It's all relative - which is where the term Potential Difference comes from.

Your "commentary" is not right when you say that the oven will not work during the negative part of the cycle. There is no difference at all as the current will just flow in the opposite direction via L and N wires. Using 'electrons' just doesn't help this at all. Do you realize that the actual amount of mean electron movement is less than 1mm in either direction? What counts is the Current and that is why 'we' all use it.

You problem with understanding the diagrams you are drawing is that they don't include the power source - which just produces PD between L and N - again, nothing to do with the Earth wire.

Why are you insisting on making your own interpretation of all this rather than reading as many links as you can (or even a BOOK!) and getting the accepted reasoning? You may need to sweat at it for a bit but at least you will get somewhere.

 

[sophiecentaur]

The N & G wires are connected at Transformer star point and brought out seperately at the recepticle. But let us assume as in your case that the N & G wires are connected locally at the recepticle by a conducting link. The G wire is actually connected to the body of the oven and is not clearly indicated in your 2nd diagram. In that case the G wire will not carry normal return current from heater, but only fault current if the live wire gets accidently connected to the body of the oven.

Coming back to your case, the return current from oven heater will now divide itself into 2 parts; one half will flow thru N wire and other half will flow thru G wire.This is because due to conducting link, the N & G wires become low resistances connected in parallel. Pls. note that the division of current will be directly proportional to the value of N & G wire resistances. If we assume that the resistance of G wire is 'zero' (practically impossible), then all of the return current from oven heater will flow thru G wire and not thru N wire. Now, if we assume the resistance of N wire to be 'zero' (again practically impossible), all of the return current from oven heater shall flow thru the N wire and not thru G wire.

So you see, current flow is relative to situation and depends on wire resistances & is not fixed. Your description of 1st diagram is correct but figure is incorrect. I think your understanding of electron current flow (AC/DC) is not clear. Try referring basics.

It doesn't divide into half, remember. It totally depends on the relative path resistances and the neutral cable will have a much lower resistance and the Earth path resistance may be several Ohms or more back to the substation or transformer.

You need to understand why an Earth wire is ever included. In a house, it's there to avoid the consequence of different bits of metal in the house having a significant Potential Difference between (shock risk). You join them all up (gas pipes, water pipes, cookers, baths etc) and you know that, if a fault ever develops on one of them (and that may not be a dead short - which the fuse would pick up probably) any current will go to Earth and the voltage on the case or pipe will never be lethal.

 

[Evil Bunny]

You need to understand why an Earth wire is ever included. In a house, it's there to avoid the consequence of different bits of metal in the house having a significant Potential Difference between (shock risk). You join them all up (gas pipes, water pipes, cookers, baths etc) and you know that, if a fault ever develops on one of them (and that may not be a dead short - which the fuse would pick up probably) any current will go to Earth and the voltage on the case or pipe will never be lethal.

Calling this conductor an Earth wire might be confusing things... The wire you're talking about is the equipment grounding conductor (according to the NEC)... In the U.S. it is either green or bare copper. It is there for the reasons you state... It's meant as a low resistance path back to the source in the case of a fault... If a fault occurs, it will travel along the equipment grounding conductor, back to the panel and up the center tap back to the transformer.

The GECs (edit: EGC equipment grounding conductor), neutrals, and the center tap of the transformer are all connected together and then connected to a rod pounded into the ground (edit: the earth), but that's a completely different discussion...

 

[sophiecentaur]

First Para is right up to a point. But I think we're stuck with the word Earth. All green/yellow striped wires are labeled 'Earth" although your term "grounding conductor would makle more sense. I certainly have lived in a remote cottage in Devon with an incredibly high Supply Earth Resistance. It would still provide protection to anyone with their feet connected to the house and who touched a faulty cooker because the internal Earth network would ensure a low PD between metalwork within the house. There was, however, a (real) Earth Leakage Trip installed, which had a Current coil in series with the Earth which opened a breaker if the Earth Current was significant (very insensitive c/w RCDs of course). The ELT would not give biological protection - just indicate a serious fault - for equipment protection.

Is the second para a different issue? I believe that the all original Earths consisted of a stake in the ground and a two-wire (overhead) supply to the house. That was a REAL Earth connection and very effective if you lived in the right part of the country.

I think painter_guy needs to read around the subject a lot more before we can get much further in helping him. Without the rudiments of Kirchoff and some formal definitions, there's no way he will get this. People are so intuitive about Electricity and that approach very seldom works.

 

[Evil Bunny]

First Para is right up to a point. But I think we're stuck with the word Earth. All green/yellow striped wires are labeled 'Earth"

Not sure where you are, but in the U.S. the National Electric Code (NEC) defines this conductor as the "equipment grounding conductor". It is either green or bare copper. You will hear electricians call it "ground" when talking casually about it...

I certainly have lived in a remote cottage in Devon with an incredibly high Supply Earth Resistance. It would still provide protection to anyone with their feet connected to the house and who touched a faulty cooker because the internal Earth network would ensure a low PD between metalwork within the house.

Coming from an AC source, you have two connection points. Current will flow out of one point and into the other point. It will go back and forth obviously, but at anyone instant in time, it will be flowing out of one side and into the other. It will never leave one side without coming back on the other side. It will never want to go into the ground (the earth, the dirt, whatever). It will only ever want to get back to the other side.

Now that being said... when we "ground" one side of this two pole AC source (by attaching a wire to one of the poles and connecting it to a metal rod we pounded into the earth), we have just invited the ground (the earth, the dirt under our feet) to become another path for the current to get back to the source. If we hadn't made this connection (with the metal rod pounded into the earth), there would be no desire for the current to travel through our bodies and return to the earth... since it only wants to return to the source. If the ground isn't connected, it is not a path back to the source.

There was, however, a (real) Earth Leakage Trip installed, which had a Current coil in series with the Earth which opened a breaker if the Earth Current was significant (very insensitive c/w RCDs of course). The ELT would not give biological protection - just indicate a serious fault - for equipment protection.

I'm not real sure what that all means... I think we are having some confusion with terminology. Where are you from?

 

[sophiecentaur]

@Evil Bunny
I'm in the UK.

It is not very helpful to be so anthropomorphic when describing any part of Science, except, possibly, when describing the higher mammalia. I never yet met an electron who actually "wanted" anything and to attribute a purpose to the behaviour of particles can only lead to misconception.
It has to be true that Kirchoff's laws apply to AC distribution and that the Impedance of all the parts determine the current that flows in them. If there is some parallel path to the Neutral line (i.e. down the Earth Line from the house), some current will flow there at all times if the Neutral is also grounded at the other ends. But are both ends grounded? They certainly aren't in my house. I can always measure a few volts between N and E, which implies that their connection is quite a long way from my consumer unit. If a fault connects the Live side to Earth, via some finite resistance, then some current will pass down the Earth connection and some will still pass down the Neutral - the total current will go through the Live line. If enough extra current flows due to the fault then a fuse will blow. Else, the fault area will get hot. In our cottage, the resistance of the Earth line was so high that it was considered unlikely that enough Earth current would flow to blow a fuse. So they installed a trip / relay / breaker which was operated by the current flowing in the Earth line and disconnected the Mains supply. This was referred to as an Earth Leakage trip. Have you not come across one of them? But whatever the state of the Earth resistance, there will be insufficient current flowing through any possible fault to give exposed metalwork a lethal potential because it is all bonded together and at very nearly exactly the same potential throughout the house.

 

[Evil Bunny]

You are correct. I read your post again, and I think my confusion came from the word "Earth". You are talking about a wire and I am talking about the dirt we walk on. In that context, I would have agreed with everything in your post. My apologies.

And yes... electrons "are attracted" to the other pole of the AC source. They do not "want" to go there, they are merely attracted there by electromotive force. Sorry... my descriptions aren't always precise. My point was that they are attracted to the other pole of the AC source and that they are not attracted to Earth (as in the dirt beneath our feet). This is a common misconception that many people have. I was trying to make that clear to the original poster.

I have not heard of an Earth leakage trip. It sounds like you are describing what I would call a http://en.wikipedia.org/wiki/Residual-current_device" ? If the current on the hot leg does not match the current on the neutral, it "trips" and opens the circuit. This is to protect against the scenario you describe where a ground fault does not allow enough current to flow to trip the main breaker.

 

[sophiecentaur]

Briefly: I am not referring to a Residual Current Device, which compares Live and Neutral currents. These did not exist at a time when transistors were not common. This device, as I keep saying, measured current flowing down the Earth wire from the consumer unit to the Earth spike. It was very insensitive but sufficient to do the job that a fuse could no.

 

[Evil Bunny]

Oh I get it... Have not heard of that. Interesting...

 

[b.shahvir]

Briefly: I am not referring to a Residual Current Device, which compares Live and Neutral currents. These did not exist at a time when transistors were not common. This device, as I keep saying, measured current flowing down the Earth wire from the consumer unit to the Earth spike. It was very insensitive but sufficient to do the job that a fuse could no.

It was known as ELCB (Earth Leakage Circuit Breaker). They were used several decades back, but now have been completely replaced by the more sensitive and fast acting RCCB's (Residual Current Circuit Breakers)