current in wires

I was long under the impression it moved all in it, but then heard or read, or saw on tv it moving on it. I asked the residential electrician who works with us, and he said he didn't know. I hope this gets cleared up, as it crossed my mind as an interesting question to finally answer.

Skin effect...I believe it flows in the outer layers of the conductor.

Del

We explored this in a previous thread concerning corrosion on wires and connectors. Unfortunately I don't remember the outcome except that it went back and forth a bit. I looked in my subscribed discussions but couldn't find it.

Electric current is an abstract notion as it is not a fluid which flows inside a tube, though nothing daunted if someone thinks so. I think so in my everyday engineering needs without any claims.

i(t)=dq/dt, so current is velocity of electric charge changing per time unit. In general the electric charge either electromagnetic field can be propagated through any matter substance, vacuum include. Metal wire is the best media which "attracts" electromagnetic field flow vector.

Skin effect when most of current density is located in wire's outer surface has most affect for AC.

In a word you can believe that most part of "current" goes inside wire when tiny resting part goes on air. By the way staying apart powerful electromagnetic field origin is capable "push out" current from wire.

bowf

Hi,

Current thorugh a wire if flow of electrons. This can be measured in terms of current, voltage when a circuit is complete with phase and neutral.

Further, the current can be detemined using a clamp on meter. This is based on the magentic flux establised when the current is flowing a conductor.

N.Suresh

Depending on the frequency.

a radio waveguide can be made from a copper 'tube' of sorts..

interesting high frequency waveguides can be made from gold deposited on a substrate.. of sorts

We would be using hollow wire over a dielectric to save a buck if all of the action were on the skin... skin effect is not taught properly in backyard conversations.

Yes it depends upon frequency but it depends also on something else like a scale factor of power line. I'm so sorry for my poor English, but I'm hopefully supposing colleagues-engineers here understand what I've meant. For high voltage 3-phase line here is the same skin-like effect for wire regardless its "low" frequency 50/60 Hz. That's why there are applied alternative geometrical configurations for high-voltage lines just to cope with this adverse factor when density of current distributed unevenly. I really do not know an exact term. Sorry again.

In SU times in Kazakhstan had been installed the only experimental 110 kV DC line (some 1500 km) with inverter stations.

So in general, any AC current "flows" through wire cut partly when another part of energy having been dispersing "on air".

Well, it depends on the frequency of the current.

I have seen micro-photographs of metal migration due to flow of electrical current, and interestingly enough, metal does not migrate in one direction, even though the current is direct current in one direction.

So, the answer to your question: it's a hard one to answer, 'cause it's hard to tell easily. One may experiment with such a thing, I would suppose, by measuring the temperature rise on the exterior of a conductor as opposed to the temperature rise on the interior of a conductor, but the thermodynamics of the setup would have to be modelled exceptionally well to account for heat transfer, thermal conductivity, thermal gradient, etc.

due to skin effect it flow maximum on outer rings & dencity reduce as you enter towards centre

Electric current is the flow of electrons. Electrons come in one end of the wire and push electrons out the other side. Valance electrons hop from atom to atom to keep the flow moving and the net charge of the wire neutral. It can be explained in far more detail if you really want all of the physics but that is the general idea. At very low frequencies or DC it is generally considered flow uniformly through the cross-sectional area of the wire. As frequency increases the alternating magnetic Fields generate opposing currents in the inner core of the wire forcing the primary current toward the outer surface of the wire. The end result is the wire becomes more resistive at higher frequencies because less of the cross-sectional area is being used to conduct the current.

Thank you for your comment and its simplicity. Can you say what happens at 60hertz. Does the current flow toward the outer surface of the wire?

Please refer to this Wikipedia page on Alternating Current, and read the heading entitled, "Effects at High Frequencies."

This explains in detail why currents tend to flow on the surface of conductors at high frequencies. The effect is not so pronounced at 60 Hz.

Current flows on the surface of the conductor..

For example 3000A bus bar in switchgear is double 1/2" X 6" bus bar typically.. The extra copper is there for nothing more than a heat sink, as heat comes with current..

does current flow through a resistor or just the surface?

Try to run those amps through a piece of copper mylar foil with the same surface area as that buss bar and see what happens... put it in a tub of non conductive heat sink gel if you like.

JE,

It has been previously stated, and makes some sense to me, that the majority of the copper is acting as heat sink.

If you were able to burry a measument probe within' the buss bar that measured current, voltage, and heat... would you only get a reading on heat?

As it has been said several times.

DC current flows throughout the entire cross section of the wire. AC current is forced away from the center of the wire due to the phenomenon called "Skin Effect." Skin Effect increases with increasing frequency and is relatively insignificant at 60Hz. High speed switching waveforms are rich in high frequency harmonics that force the current toward the outer skin of the wire. Try Googling "Skin Effect in Conductors" or "Skin Effect at High Frequencies." You are bound to find good information. After that try "Proximity Effect" That is the AC current in one wire effecting adjacent wires in a similar way that "Skin Effect" is caused. Both are dealt with on a regular basis in switch-mode transformers because of the high speed transitions and high frequency harmonics.

I really would like to know, if DC have any impact at all on the skin effect ? Because, as i recall, electron repulse each other... as in an electrical field, which would mean that all electrons would be in the outer area of the conductor in a DC system. If enough voltage is put in the conductor there would be a jump to nearest lower potential. But how come there is no information about the DC skin effects to read, but lots of AC and skin effects ?