Electricity Travels In or On the Wire?

the "core" volume is necessary to dissipate the heat created by resistance.

How the core can dissipate the heat?

GA from me. That is also a reason, besides flexibility, why they strand thicker core too.

electricity travels on the wire surface

Outdoor Substation PI mounted BUS Bars are Hollow section of Copper. For Hollow tube selecion, one reason is Skin effect. Others Cooling, Rigidity, Costs etc.

It matters to the electrons. They like to have window seats...

Actually the shape of a conductor can make all of the difference in the world.

Take a look at all the shapes of antennas? While a crumple of foil and wire may have worked for the old TV and radio..

..Some types of transmission waveguides actually require the use of square tube or in some cases gold or silver that has been applied in vapor deposition to a flat insulator..

...Look at it this way.. Both he and his boss were correct.

It's the frequency that matters the most, so I would mention both when writing to clear it up for the readers.

...You will never see a DC wireless transceiver that uses a DC 'wave'.... So without a frequency 'wave' the current stays at the zero crossing point.. ..which is the center. think about that for a moment.

You have explained why the Aluminium Tube Taking the Signal to the Top of High Micro-wave towers, was round Smooth on the outside, with a retangular hollow center, which spiralled at a given rate dependant on the Carrier Frequency being Transmitted. Retired Micro-Wave Maintenance Tech.

That's right..

Even though I don't have hands on experience microwave transmitters beyond a few of box sized units that have come about in recent years.. (The type used to transceive data a few hundred or thousands of feet.) I have had nothing but profound respect for the system of microwave towers... Literally beaming information in a direct line of sight over the horizon to the next tower etc..

I would look at the towers as a kid and wonder what they did, so when i started to research them and then learn about waveguides in school.. It was all very cool. If you want to understand the forces of the universe and behavioral characteristics of electrons.. It's a pretty good subject to get into.

Maybe it was just a j o b to you, but I'll bet it had some pretty cool moments and some eureka! moments as well.

JE

Some minor mis-spelling in your 5th paragraph. It should be:

IT'S THE FREQUENCY THAT MATTERS THE MOST,

I get so tired of audiophiles worrying about skin effect because some salesman at the store (who does not know fecal material from shoe polish) told them about it.

At audio frequencies, skin effect is virtually non-existant.

Bill

also GA

Please note though... electrons travel .. and the other way

I'm not so sure the electrons travel as much as they get really excited and bump into each other really hard.

Otherwise when you shut off a switch, there would be a lot of them jammed up at the end of the wire and it would glow in the dark.

Quite right you are, they bump into each other.

I always thought it sort of like traffic in the city: Even in bad traffic eventually the electrons get there.

At traffic lights, stop signs, and traffic cops, the cars are like electrons: they just keep filling the holes.

Is the spark plug supply a good example?

Imagine a V6 at 6000RPM makes 100 RPS (revolutions per second)

The pulse train is 6 times less in chopped DC frequency or 16 Hz at that speed

The skin effect has to do with the high voltage peaks there, not the frequency. IMO

I was waiting for someone to say this. GA

Now, I suppose if the editor of the car magazine was making some statement regarding the spectral content due to the rising edge of the spark pulse, then we might be on to something. But I seriously doubt it . . . He's just an idiot under-informed person with a (very) little bit of knowledge.

Is the spark plug supply a good example? Imagine a V6 at 6000RPM makes 100 RPS (revolutions per second) The pulse train is 6 times less in chopped DC frequency or 16 Hz at that speed The skin effect has to do with the high voltage peaks there, not the frequency. IMO ...erm, not even that. An individual cylinder of a four-stroke engine fires on every other revolution.

Sorry, but I agree with him; less resistance

When alternating current flows through a conductor, there is maximum no. of magnetic lines present at the center of the conductor, which results into more resistance at the center part of the conductor.

As you go away from the center, the strengh of the magnetic lines reduces and therefore the resistance is less on the outer part "Skin" of the conductor and current flows through skin of the conductor which is less resistive path.

The skin thicknness depends on the frequency of alternating current. Higher the frequency, higher resistance at the center of the conductor.

Not sure if this will help but here it is anyway:

Quote "Looking for "electricity" inside wires would be as foolish as collecting rainwater in order to look for tiny pieces of "weather" in the water." I think you need to define what you are talking about before you get an answer.

The quote was taken from http://amasci.com/miscon/curstat.html.

GA AGuest... thanks for the quote and link. I was going to give a GA to Jr for making me laugh (window seats), but only one per thread is allowed.

Their is an effect that is called skin effect. This states that as the frequency goes up the electricity as you call it ONLY travels in the scin area leaving the core unused. The formular for this is along the lines of "the depth of Penetration in cm = 7.5 X frequency raised to the power of -0.5.

This will effect transformers running at 50kHz for instance but have no effect on DC curent when the most basic OHMS LAW tells you what is happening.

Even at DC there can be a slight skin effect in thick cables if the cable carries very high currents, probably because of internal heating of the cable, and therefore increased resistivity, compared with the outside of the cable.

The 'skin effect' as it's known affects cables carrying ac current, the higher the frequency the more the current travels in the outer surface of the conductor. This is why we go to multi-strand or Litz wire which has thinner wires strands, but more of them giving greater surface area. At radar frequencies the conductors become wave-guides which are hollow section tubes, all outer skin and no inner core.

If you are working in automotive restoration the cables will most likely be carrying dc currents and you should only be concerned with current carrying capacity and flexibility of looms. Modern vehicles now use cables carrying data streams at high frequency which are very much affected by the skin effect and cross coupling between wires.

After reading many posts explaning the skin effect, now I am curious to know

How some one realized this phenomenon

How he/she proved it and

how we can observe and experience that it really happens so?

Your question can be open ended unless you wish to sit for a doctorate in electrical engineering. Meanwhile look up Litz wire .com or huge amount of electronic information available on ac theory; transformers;transmitters and the like.

Take a PC an index finger and an enquiring mind and you will bore down to ANY of the information you want to find (and a lot you dont need to know)

CR4 is a good place to start ! !

Lord Kelvin is supposed to have shown it first, followed by many good scientists/engineers. Here is the link again to the excellent paper from Schneider on this subject : ect83.pdf

This is how the paper starts ...

Thanks KVS

Hope I will get answers to all my curiosities

Regards

It may be helpful to think in terms of rate of change of current rather than frequency. A lightning strike has a very large rate of change of current hence lightning conductors have a large suface to volume ratio ( a thin flat strip of copper ).

OK, let's get very basic with this explanation.Like charges repel each other.All electrons are negative.They do not like being forced together, they tend to repel towards the outside of the conductor.The higher the voltage or frequency applied, the harder they push away from each other.This repulsive effect can reach the point where the electrons actually latch onto anything to get away from their neighbor,even an air molecule, thus producing ionized air.It can use this ionized air to assist others in escaping from the crowded neighborhood of the wire surface.If the ionized air molecules come in contact with, or sufficiently close to an uncharged or lesser charged object,the electron will attach itself to it.If it has a bunch of neighboring ions nearby, they can all get together and jump a gap to a nearby ground,therby dissipating and finally getting away from rubbing elbows with other electrons.

As stated, the higher the voltage, the more repelled they are by each other,also high frequency as a similar effect.So, on low voltage, low frequency,low current applications, the electrons occupy almost the entire area of the conductor.This includes household voltage,direct current,including most automotive applications.

I have seen a 1/4 copper tube carrying 150 amps at 50 Khz,with water circulating inside of the tubing for cooling,and there are more extreme examples of skin effect,but again, it is irrelevant at low frequencies and can for the most part be ignored.

Radio waves are no DC, in no ways; have you heard of "modulation" ? because that's what makes the trick.

Yahlasit

Dear it is just because of the skin effect that electrical power do flow on the wire not in the wire...

Okay, let's stir this pot a little further…

Lightning is DC current, agreed? Why can you dive under water, and be safe during a lightning-storm???

(The lightning travels along the surface of the water. If it didn't, all of the fish would be fried every day…)

The sea is at ground potential the effect of lightning is the very high voltage produced by electrostatic means wishes to get rid of this charge by grounding itself i.e. going to earth (sea). Once in the sea there is no flow of current as the high voltage is now grounded or earthed

a shock is only felt if there is a potential difference between say both arms both legs etc. you can step on the live track at a rail junction for instance if you put both feet on (and off) at the same instance.[dont try if your balance is not 100%]

This is not put well but think before you write.

.. So stand in the water and duck under when you see lightening?

Dive in when you see it?

or just stay submerged for the worst part of the storm?

I'm interested to know what you think as I like to be near the lake when it storms..

..Thanks in advance!

Eh, not exactly.... First off your assumptions are incorrect. Secondly your understanding of your assumptions are incorrect as well.

Lightning is not actually DC, it actually bounces back and forth between the cloud and the ground several times before the energy is spent, with the first (usually invisible) "stroke" actually moving from the ground upwards to the cloud. that stroke ionizes more of the air, making it more conductive, and the downward stroke then follows that path back downwards. This is all relatively new information that has been learned in the last say 30 years or so, mainly because we didn't have the equipment to study it in detail and everyone made assumptions about lightning, just as you did.

Now, very short duration DC signals are mathematically the same as AC signals. Think about it, what do you get if you have an AC signal that only persists for the time of half it's cycle? You have a very short duration DC signal!

now what is it about AC that makes it different than DC? changing current levels. in DC there are only two periods of changing current when you turn it on, and when you turn it off. in AC there are two current changes with each cycle. but if you turn DC on and off very quickly, you are essentially making AC.

Here is a typical electrostatic discharge waveform (what you get when you scuff your feet across the carpet and touch the doorknob) which is essentially a single stroke of lightning on a very very small scale. only about 5000V or so at it's peak typically.

Notice the time between 0% and 100% is virtually nil? We are talking a nanosecond at most. that "rise time" is one quarter of a AC sine wave with a period of between 2.8 and 4 nanoseconds. That is actually around 250,000,000hz or more. THAT is a high frequency signal.

Consider the amount of current carried by the water- after the strike, the electrical charge is dissipated into an almost infinitely large conductor, so the resulting current flow at any part of the water is nearly impossible to measure, let alone cause any damage or harm.

Electricity is mixed of two energy system. Electromagnetic wave. Magnetic wave is skin effect Electron is cloud and cloud in contact to atmopheric condition and electron cloud moves on the surface and is skin effect and is effect by humidity conditions and others.

Second one is embedded electron cloud which not only transport electron but also generates heat and comes with rating because of metal ability to remove heat by conduction. We can buy different diameter solid and hollow wire based on our needs to carry amp.

Last one is Magnetic portion of the electric energy and this flow in the direction of electron flow

AC concentrates on the surface, this is called skin effect. Its effective penetration is limited to an approximate depth of one wavelength while DC travels throughout the cross section, more or less uniformly. Hence the thickness / diameter requirement for the latter would be more. Also, thickness / diameter depends on amperage. More amperage would require thicker conductors to minimize heating losses . Resistance to electric current is proportional to area of cross section of the conductor

"Resistance to electric current is proportional to area of cross section of the conductor"

Resistance is inversely proportional to the cross sectional area of the conductor.

Look up 'Skin Effect'. As frequency of an AC signal increases, the signal actually propagates toward the outside of the conductor it travels through. At very low frequencies, it is safe to assume the whole conductor cross-section is being used. Same assumption can be made for DC signals. This is something that is taught in Radio Frequency design and is why waveguides actually improve efficiency at higher frequencies.

Functionally the electricity will flow through the least resistant path. As metals heat up, the electrical resistance increases thus the cooler outer surface will carry more electrons. There are MIL and NEC specifications for current carrying capacities which incorporate more than just this phenomenon, but in general the resistance of a conductor relates to the cross section. This could be explained as electricity conducting through more than just the outer surface of the wire. My early reference was an out-of-print book by Herbert C. Roters (C)1941. Ask your local wire manufacturer for more current reference material.

All i know about electricity in a conductor or wire is that it travels along the whole cross-sectional area of the conductor or wire carrying the load,wether AC or DC .

He is basicaly correct

If you google "skin effect in electrical wiring" you should get lots of reading material

And He Is Right: All electricity travels along the outside of the wire, rotating around the wire as it goes, and the Right Hand Thumb rule; if you wrape you fingers around the conductor your thumb points in the direction of the Magnetic Field Produced.

heard about skin effect.???..ex. is an ACSR cable..the center of the cable is steel reinforced..this because of the electrons property to crowd the outer core of the conductor..the steel there is just to have an increased tensile strength..so what the editor means was the "skin-effect"...so your editor is half-way right..

Wow. What a response. You asked about an automobile, and learnt about (a) power wiring in 3-phase, (b) Lightining, (c) Other kinds of surges, (d) No problem if you have less than 5/8"(16mm) cables.

So on.

i am sure i learnt something new. i am sure you have too.

Bottom line is... have you enough ammo now to face that "Ed Crankshaft"?

wow again. i just checked. The OP has never reacted to ANY comment on this thread. i sign off. Final.

Kvsridhar, that is usually how it goes around here, the OP will drop in, ask a question, and disappear, never to be heard from again. rather irritating to tell the truth. It'd be nice to get a "thank you" once in a while.

Still pisses one off. i mean what the heck? You bet that the least one can do is a 'thanks to you all guys. Not that you helped any."

But then... this is LEHMAN. A responsible member as i know from his/her posts on other fora.

So .. let's give the benefit of doubt. Maybe he got sent overseas...

Oh, I would not say we didn't help. I think the point we all brought up in discussing the skin effect was to explain how both he and his editor may have been mislead. The question did not have a yes/no answer, it was one of those things that depended on the situation. Hopefully both he and his editor came away with a more fundamental understanding of the subject. But since we never heard back from Lehman, we'll never know....

Of course we all helped. i put in whatever i knew, and learnt some.

What i meant was, like 'beauty is in the eye of the beholder'....has Lehman learnt something ? If not, whatever we have shared has enriched our own knowledge, but hasn't really made him understand perhaps?

Thats the beauty of CR4 for me. OP asks an inane question, and some beautiful answers give me 'collateral knowledge'...great

Yes, I learned something; now to try to transmit all this stuff to the editor.

I was in the transmission & distribution field for years and never heard of the skin effect! Probably because I was in the part that built the supporting towers (round tubes in our case, not lattice), but did not do design work of the actual conductor size and arrangement, nor the routing of the transmission line.

See reply to #56 I guess the computer was utilizing Murphy's Law! And dipping my name in mud!! Thanks.

Apologies if i said something that upset you in any way... i thought some force majeure situation...like this one ?

Good one.

Surely there must be number of such pictures with you. Canyou please share.

Regards

Courtesy my aunt who used to bring me Murphy calendars, yes, i have a small hilarious collection. If you can send me your mail ID via CR4 mail system, i can send some..

This is the OP. I couldn't very well reply, because the computer refused to open the thread to I could read the replies. Today it started to work again--I don't know why. My immediate concern was small gage wiring carrying DC in an automobile, but I have learned about the skin effect in AC conductors. In transmission conductors (ACSR) with AC apparently the skin effect is well-known; along the line I heard about corona although that word wasn't used. With DC the current is carried across the whole cross section of the wire, especially for the small gages used in automobiles. And with small gages the skin effect is negligible, so AC and DC both are carried across the whole conductor cross section.

Thanks to everybody for their help.

thanks for getting back to us lehman, it is good to get some feedback.

I'll verify that. Cannot Get Replies

Anybody who likes John Deeres can't be all bad.

Had a friend who worked for them back in Iowa for many long years. When his wife left him though, she sent him a John Deere letter.

Bill

Yes. He is right. Due to the phenomenon of skin effect, the current has a tendency to travel along the surface of the conductor. However, it is more relevant in case HV and Extra HV conductor systems.

BB Raina

It's not the voltage, it is the frequency....

Thank you so much for the post. It's really informative!

_________________

CR4 Admin: Removed advertising from this post.

Dear Mr. Lehman57,

The current flows in the outer periphery of the conductor and at the centre it is NIL or Less.

For very high frequencies, for example Radio Frequencies, the conductor will be hollow,

as the current will flow at the outer periphery.

DHAYANANDHAN.S

Electricity travels using few known path

Path # 1. Moving through cloud of electron from one end to other end under applied voltage.

This is caused by metal atoms forming cloud above atoms. The total diameter then has different cloud layers and each layer is carrying electrical current. If we add an items of oxide then cloud is broken. If this breakage is more then resistance to flow increases and part of electrical current is lossed and result is heat generation.

Other is ionic conduction. Alkali ions are good example they move from one end to another and during movement carries electron which is dumped other end.

First process is fast and last one is slow but both does.

Electricity travels through inside a wire. As the frequency increases or the current increases, the flow is nearer to the surface.

At audio frequencies the skin effect depth of penetration is about 1 millimetre, so yes, ordinary wire of around 2 mm diameter or less is adequate for connections.

only half right, current is irrelevant to the depth of the skin effect. frequency only determines that.