[SOLVED] Why basic concepts of electricity are so complicated

[tahir4awan]

I have been learning electronics for many years but still there are some concepts which are uncleared. Although there are thousands of book about electronics but strangely they are all same in explanations. Here are some questions which arise in beginners mind,

1. AC has no polarity:
because ac has no polarity, we can connect wires without thinking, which is phase and which in neutral.
but what I understood, voltage at ac neutral is 0 volts. It is the current which changes direction and it is the live wire which experiences both change in magnitude and direction. If it true that neutral stays at 0, then why we say that polarity in ac is not important.

2. Electric shock with neutral wire:
as name implies neutral, then why we experience electric shock. Some say, because it changes direction, that's why it happens. But as I said, is the current which
changes direction but with 0 volts.

3. Electric shock with insulation:
current doesn't flow from insulators. Which is true, even with thin paper current cannot pass. Then why we experience shock with shoes.

4. Earth is a good conductor:
we experience in daily life that current does pass through earth, but where do electrons go. Do they travel through unlimited earth or do they travel to nearby electric poles or do they travel to the generation plant? which seems illogical. For electrons to flow here must be a closed circuit. This circuit must have a battery or generator which force electrons to flow and on the other side they receive electrons back. So where do electrons flow in earth?

Thanks in advance

 

[barry]

1) Nobody says polarity is not important. Look at ANY basic wiring book, local electric code, whatever, and it will clearly make a distinction between HOT and NEUTRAL.
2) If your building is properly wired, neutral is connected to ground (earth). If you're getting a shock touching neutral, then either the wiring is faulty, or some other part of your body is connected to a source that is different than ground.
3) Maybe you have electric shoes. Or maybe current is going through a different path, from one arm to another, for example.
4) No,the earth is a terrible conductor. Current does not "flow through the earth" in the way that you're thinking. Put an ammeter in the path between your source and the earth and you'll not see any current flow.

 

[tahir4awan]

Thanks for your relpy but still qurstions,
1. From polarity I mean in Hause sockets, it doesn't say which is live or which is neutral. You check with tester for live Wire. My qurstion.was, why they are not labeled in sockets Just Like DC. I mean it safety reasoms. Theoratically If the circuit is closed, then there should be no Problem in touching neutral Wire. Yes I Know in books, mentioned with polarity,. But my question was related to Hause Wiring.

Secondly If the neutral Wire stays at 0 Bolts, then why in a closed AC circuit, the phase tester shows phase on both conductors?

3.. People say that, you recieve shock, because shoes were good, but It makes no sense, electric wires have thin layer of insulation and current does not pass through it, but It passes through shoe? If I am not touching other Objekt, then my body is an open circuit, then how come current flows through my Body?

4. That was my question, If earth is a bad conductors, then how PE works, PE Resistnace must be less than 5 Ohms. And PE can work as neutral Wire. Then how come earth a bad conductor? Then where do electrons go?

 

[KlausST]

Hi,

1. From polarity I mean in Hause sockets, it doesn't say which is live or which is neutral. You check with tester for live Wire. My qurstion.was, why they are not labeled in sockets Just Like DC. I mean it safety reasoms. Theoratically If the circuit is closed, then there should be no Problem in touching neutral Wire. Yes I Know in books, mentioned with polarity,. But my question was related to Hause Wiring.

I think you answered it yourself. For safety reasons you need to protect (isolate) both neutral and live the same way. You need to treat them identically. ... then there is no benefit when you label them. For the load it is no difference anyway.

3.. People say that, you recieve shock, because shoes were good, but It makes no sense, electric wires have thin layer of insulation and current does not pass through it, but It passes through shoe? If I am not touching other Objekt, then my body is an open circuit, then how come current flows through my Body?

human body is humid. In your shoes there will be humidity. Thus the current will find it's way through shoes. And there is capacitance. AC will flow in either case ... even with the best isolation.
But with well isolated shoes the current will be low...theoretically when you touch live wires (I really don't recommend to do this) the current may be low enough not to be dangerous - maybe you even can't recognize it.

4. That was my question, If earth is a bad conductors, then how PE works, PE Resistnace must be less than 5 Ohms. And PE can work as neutral Wire. Then how come earth a bad conductor? Then where do electrons go?

One can not predict Earth resistance, it depends on structure, humidity ....
But to increase safety it does not need to be very low ohmic.
We have RCDs that usually trip at 30mA. No need for low ohmic paths.
And an earth rod or earth band around your hose helps to "equalize" the neutral voltage.

Example:
Maybe from distribution station to your house there is a "neutral" voltage shift of 20V. So if you could measure the voltage of your house neutral to a real zero neutral then you will see 20V.
But your house neutral (protective) is connected with earth band thus all your house(environment) is lifted to the same 20V...so the 20V neutral wire with respect to your 20V environment it will result in zero voltage.

Klaus

 

[c_mitra]

1. AC has no polarity:
because ac has no polarity, we can connect wires without thinking, which is phase and which in neutral.
but what I understood, voltage at ac neutral is 0 volts. It is the current which changes direction and it is the live wire which experiences both change in magnitude and direction. If it true that neutral stays at 0, then why we say that polarity in ac is not important.

AC has polarity but it keeps on changing. How fast it changes depends on the frequency. Because the polarity changes, we cannot say one is positive and the other is negative.

Compare with a simple 1.5v cell. The zinc body is negative and the central carbon rod is positive. But you must understand that the central electrode is positive with respect to the zinc body. This is important because we can only measure potential difference and not the absolute potential. It is the same if you say that the zinc body is at a lower potential compared to the central electrode.

If you consider the neutral and the line, it is same. The potential difference between the two changes continuously. For the house power supply, at the rate of 50 cycles per second. For an electrical appliance, which one is line and which one is neutral does not matter.

For safety reason (and another less obvious) one of these two (neutral one precisely) is grounded somewhere and has zero potential with respect to the ground at all times. The other conductor now shows +/- 220V (or whatever the line voltage in your area) at the designated frequency.

This is useful from the power distribution point also.

2. Electric shock with neutral wire:
as name implies neutral, then why we experience electric shock. Some say, because it changes direction, that's why it happens. But as I said, is the current which changes direction but with 0 volts.

You should not get a shock if you touch the neutral wire (because somewhere it is connected to the ground). There is another earth connection (local earth) present in 3-pin power connections.

There will be current flowing through the neutral and that shall cause a voltage drop. So there may be 10-20V present at the power socket with respect to the local ground terminal. But it should not be enough to give you a shock. Just test with a neon tester.

3. Electric shock with insulation:
current doesn't flow from insulators. Which is true, even with thin paper current cannot pass. Then why we experience shock with shoes.

Shoes are not good insulators. The sole is PVC but often mixed with carbon powder to make it conducting. Some soles are non conducting but you need a very small current to get a shock. With a current of 10-100uA, you will get a tingling sensation and a current of 10mA or more can be fatal. A current of 1mA passing through the heart can be fatal (please check the number; I quote from memory)

 

[KlausST]

Hi,

The sole is PVC but often mixed with carbon powder to make it conducting

I didn´t think of carbon powder in PVC. That makes sense.
And maybe they use carbon powder, because it makes the soles black and is cheap.

Klaus

But the inital question was: Why it is that complicated?
It is not "artificially" made complicated. It follows the rules of physics. One can not ignore them.
And maybe because we need to live and calculate with "imperfections".
Earth GND is not perfect, electrical wires are not perfect, electrical isolators are not perfect.
Maybe your house installtion is not perfect..
Humans are not perfect. Human body electrical behaviour is not perfect. Maybe one person can touch 100V and nothing happens, maybe another person does exactly the same and dies. --> So don´t test it.

 

[tahir4awan]

AC has polarity but it keeps on changing. How fast it changes depends on the frequency. Because the polarity changes, we cannot say one is positive and the other is negative.

Compare with a simple 1.5v cell. The zinc body is negative and the central carbon rod is positive. But you must understand that the central electrode is positive with respect to the zinc body. This is important because we can only measure potential difference and not the absolute potential. It is the same if you say that the zinc body is at a lower potential compared to the central electrode.

Here I am confused again. Is it AC voltage which and current which change direction and magnitude in live wire. In neutral wire which is at 0 volts. It is the current which changes.

When you say AC changes polarity, it seems that, for half cycle live wire is at 220v and for other half cycle neutral wire is at 220v. Am I right?

 

[c_mitra]

When you say AC changes polarity, it seems that, for half cycle live wire is at 220v and for other half cycle neutral wire is at 220v. Am I right?

Technically no.

You need to talk about potential difference only.

Yes, you can say for 1/2 cycle, line voltage is 200V and the neutral voltage is 0. For the next 1/2 cycle, the neutral voltage is 220V and the line voltage is zero. But this is not really accurate.

Accurate statement will be

The potential difference between the line and the neutral is 220V for 1/2 cycle and -220V for the next 1/2 cycle.

 

[tahir4awan]

Technically no.

You need to talk about potential difference only.

Yes, you can say for 1/2 cycle, line voltage is 200V and the neutral voltage is 0. For the next 1/2 cycle, the neutral voltage is 220V and the line voltage is zero. But this is not really accurate.

Accurate statement will be

The potential difference between the line and the neutral is 220V for 1/2 cycle and -220V for the next 1/2 cycle.

Some years ago I have the same concept you described. But it does not satisfy me. Because,
1. When neutral wire for half cycle is at 220v then why in socket neutral wire remains at 0 volts.

2. In house distribution board you always connect neutral wire with PE. Which is a prove that neutral always r mains at 0 volts.

3. In sine wave graph the reference line is 0 volts. Then which wire is reference.? It is 220 volts with reference to neutral wire.

4. I have seen people touching neutral wire in closed circuit but not the live wire.

5. If they act same in a closed circuit, than what is the use of calling them live and neutral wire.

 

[betwixt]

Think what the letters AC stand for: Alternating Current.

All voltages are measured relative to some other point, using the 1.5V analogy cell is it right to say the outside case of the battery is zero and the middle is positive - or- is it right to say the middle is zero and the case is negative? The answer is neither is correct, the voltage only exists between them. Try measuring the voltage between one side of the battery and Earth, then the other side of the battery and Earth and you will see what I mean.

Neutral is only nominally zero because it has a connection to Earth somewhere. The 'live' wire alternates between positive and negative relative to the neutral wire. If you switched the Earth connection from neutral to the live wire at source, the voltage between them would be exactly the same but now the names of the wires could also be swapped.

In some countries, on single phase supplies they make no distinction between live and neutral and plugs can be inserted either way around. Functionally both systems work equally well but there is some sense in knowing which is which. For example a fuse in the neutral line might blow leaving everything 'live' but the same current flowing through a fuse in the live line would leave everything 'dead'. Similarly, for safety reasons it makes sense to put switches in the live line so it is safer to touch equipment that is switched off. You might have noticed almost all equipment uses double-pole switches, breaking both the incoming power wires, this is done to be sure the live is disconnected whichever way around the plug is inserted or the mains socket is wired.

Brian.

 

[tahir4awan]

When I measure battery positive with ground it will show 1.5 volts and when negative terminal with ground it will show 0 volts. Positive terminal means it has force to move the electrons and neutral ist the return path to battery.

As you can see in pictures. It is clearly stated, neutral wire always remain at 0 volts.

--- Updated Dec 19, 2020 ---

The reasons I have posted this topic. Because there are so many opinions about ac. But what is right and standard. I don't know. As I said in books normally, it is written AC changes direction. But know explanation about what is really happening in two wires. Normally it gives a picture in book stating reversing direction of current. But the main point is voltage. No mention of role of voltage in neutral wire.

As I posted pictures of articles, it is clearly stated, neutral wire serves as reference oder 0 Volt. And not that it will serve as a reference for half cycle than for other half cycle neutral will be at 220 volts.

 

[betwixt]

Half cycles doesn't mean anything in this context. The articles are correct but you have to take a somewhat abstract view of what the voltage is across. All that matters to the load is that it has two wires and between them there is a voltage reversing in polarity. If the neutral was disconnected from Earth everything would still work exactly as before but then both lines could have ANY voltage on them with respect to Earth and that could be dangerous. Electricity arrives at your local transformer at high voltage (here its 11.75KV) and the transformer secondary is completely isolated from the primary side so although it has (here) 230V at it's output across the output lines to houses, both wires could theoretically 'float' at any reasonable voltage randomly. For example, 230V between live and neutral but both being 5KV above Earth! Equipment connected across live and neutral would only see the 230V but there would be serious insulation problems and a high risk of electric shock. Earthing one side and calling it neutral removes that risk.

Brian.

 

[Easy peasy]

reading a lot of basic text's on electricity should help you - books are far better than the internet for gaining a good grasp of fundamentals - without such a grounding ( no pun intended ) everything will be very confusing ( unless your IQ is very high )

 

[c_mitra]

When I measure battery positive with ground it will show 1.5 volts and when negative terminal with ground it will show 0 volts.

This cannot be correct. We call a battery "a floating device", the potentials are not referenced to earth. Just like the secondaries of a transformer.

When you connect two batteries in series, the zero of one cell is now raised to 1.5V. That would not have been possible if the case of the battery is having an absolute potential value (of zero).

Think over it.

 

[c_mitra]

As I posted pictures of articles, it is clearly stated, neutral wire serves as reference oder 0 Volt.

It is both true and false.

It is false in the sense that single point potentials cannot be measured. Have you ever seen a multimeter with only one probe that can be used to measure voltage at any given point?

It is true in the sense that in this context, we implicitly assume that the earth potential is zero. This is very convenient because we can measure potential difference with respect to the earth ground at different places. We assume that earth is a decent conductor and has a const potential on the surface (that can be arbitrarily set at zero).

Consider this:

A generator (of electric power) has the body grounded at the local earth point for safety reason.

It produces three phase electric power without any neutral. If the load is balanced, all the three phases deliver equal RMS current, then we do not need a neutral.

During power transmission we do not use a neutral because it is not needed.

At your home, we need a neutral because you use only one phase. This neutral is grounded at the local distribution transformer site. So it is correct to say that neutral has zero potential with respect to the earth ground.

It is likely that your house has three phase supply. Therefore different circuits are connected to different phases.

 

[Akanimo]

Some years ago I have the same concept you described. But it does not satisfy me. Because,
1. When neutral wire for half cycle is at 220v then why in socket neutral wire remains at 0 volts.
...

You are confusing peak voltage and RMS. In the half cycle that you are referring to, the voltage rises sinusoidally from 0V to Vpeak=(-1)*220*1.414 and back to 0V w.r.t the NEUTRAL. So the peak on the HOT is negative rather than the NEUTRAL being (+1)*220*1.414. So the NEUTRAL is at 0V.

--- Updated Dec 20, 2020 ---

You should be looking at the concept with the peak voltage rather than the RMS. The use of RMS doesn't come to play at all in this analysis.

 

[Transight]

The reasons I have posted this topic. Because there are so many opinions about ac. But what is right and standard. I don't know. As I said in books normally, it is written AC changes direction. But know explanation about what is really happening in two wires. Normally it gives a picture in book stating reversing direction of current. But the main point is voltage. No mention of role of voltage in neutral wire.

The power companies deliver the enegy we need to our homes etc., through transmission towers at a kilovolt AC range to reduce losses, then fed to different step down transformers to reduce the voltage that our appliances use, these transformers mostly are center tapped for example 120-0-120 depends on your country, tapping on 120- 120 will give you 240V AC and either side 120-0 will give you 120V AC. Remember voltage is the potential difference between two points, the choice of the return path is trivial since this is AC, grounding in the power transformer is done at the center tap point which is the same as the neutral (0V reference) side. You should see 3 wires coming into your home to safely say that the power outlet of my house can be safely grounded otherwise the earth ground will be floating.

 

[barry]

I cannot believe how people are getting themselves tied up in knots over this. Certainly making it waaaaaay more complicated than it is. The OP seems, for some reason, completely resistant to straightforward answers.

I guess the answer to your original question “Why basic concepts of electricity are so complicated?” Is: ‘Because you choose to make it so.’

 

[zenerbjt]

i am sorry for you, you have read too many books without being able to get making some circuits. Because when you make the circuits , you only then will form your understanding. If only books you read, (and you make no hardware) then your mind will play tricks on you like it is now.
When you design a circuit to do something, and it works , and you see it being sold, because it works, then you soon undertsand......or rather, you "form" an understanding.
If anybody tries to understand completely the science of electricity before they start building hardware, then they will never understand, and never get started in building hardware..

 

[Ratch]

To the ineffable All,

Electrical science has embraced a few quirks and misnomers that should have been corrected a long time ago. I will list a couple of them below.

1) Ohm's Law is NOT R =V/I . That formula is the definition of resistance. A definition is not a law. The true meaning of Ohm's Law pertains to the linear resistance of a piece of material during voltage changes. A copper wire follows Ohm's Law. A junction diode does not. I can provide documentation for my assertion if anyone wishes.

2) The phrase "current flow" literally means "charge flow flow", which is redundant and ridiculous. At the very least it is poor English. Yet it is frequently spoken by those who should know better. Instead one should just say "current", or "current exists", or "current is present" , whichever is appropriate

Ground has become synonymous with a circuit voltage reference point. Naturally we want our houses and electrical machinery to be at the same potential as the earth we stand on, so we "ground" them.

Ratch