Confused points. The Skin Effect, and attenuation.

[Gryd3]

I have recently re-learned the skin effect, and how (at higher frequencies) the outermost skin of a conductor will conduct better than the center inner-most portion of the conductor.
I have also been reading some articles regarding networking cable and have come across the mention numerous times that stranded wire has a higher attenuation...

https://www.andcable.com/files/UnderstandingStrandedandSolidWiring.pdf

2. Higher frequencies
At higher frequencies, conducting materials like copper experience a continuous decrease in their conducting cross section, called the skin effect. As the frequency of a transmitted signal increases, the skin effect pushes electrons outward toward the surface (“skin”) of the conductor. As the frequencies
continue to increase, the skin depth continues to decrease, so that a cylindrical, solid conducting path will become hollowed out, with electrons flowing only along the outer surface of the cylinder. In this way, the smaller and less-defined circumference of stranded conductors results in higher attenuation losses (as much as 20% higher) in stranded cables than in solid-conductor cables.

But if the skin effect resulted in stranded cable having a lower resistance than a solid conductor, would the reverse not be true?

I have two 'truths' that are conflicting. This is the internet of course, so these truths are not 'The Truth' but are my current understanding belief.

Is this perhaps due to other effects not mentioned like inductance or capacitance within the wire?

 

[hevans1944]

I have recently re-learned the skin effect, and how (at higher frequencies) the outermost skin of a conductor will conduct better than the center inner-most portion of the conductor.
I have also been reading some articles regarding networking cable and have come across the mention numerous times that stranded wire has a higher attenuation...

https://www.andcable.com/files/UnderstandingStrandedandSolidWiring.pdf


But if the skin effect resulted in stranded cable having a lower resistance than a solid conductor, would the reverse not be true? Skin effect results in wire with stranded conductors to have a higher parallel resistance than the same diameter solid wire.

I have two 'truths' that are conflicting. This is the internet of course, so these truths are not 'The Truth' but are my current understanding belief.

Is this perhaps due to other effects not mentioned like inductance or capacitance within the wire?

Inductance and capacitance have nothing at all to do with skin effect, which is caused by opposing eddy currents flowing in the conductor. Distributed inductance and capacitance affect the impedance of a wire considered as a transmission line.

 

[Gryd3]

Inductance and capacitance have nothing at all to do with skin effect, which is caused by opposing eddy currents flowing in the conductor. Distributed inductance and capacitance affect the impedance of a wire considered as a transmission line.

Yes, that part I understand, but what in a stranded wire would cause more attenuation than in a solid conductor of the same cross-sectional-area?
It's the second part I do not quite grasp yet.

 

[davenn]

hi Gyrd3

from another wiki page ......

At high frequencies, current travels near the surface of the wire because of the skin effect, resulting in increased power loss in the wire. Stranded wire might seem to reduce this effect, since the total surface area of the strands is greater than the surface area of the equivalent solid wire, but ordinary stranded wire does not reduce the skin effect because all the strands are short-circuited together and behave as a single conductor. A stranded wire will have higher resistance than a solid wire of the same diameter because the cross-section of the stranded wire is not all copper; there are unavoidable gaps between the strands (this is the circle packing problem for circles within a circle). A stranded wire with the same cross-section of conductor as a solid wire is said to have the same equivalent gauge and is always a larger diameter.
However, for many high-frequency applications, proximity effect is more severe than skin effect, and in some limited cases, simple stranded wire can reduce proximity effect. For better performance at high frequencies, litz wire, which has the individual strands insulated and twisted in special patterns, may be used.

maybe that clears it up ---- it says it better than I can express it myself.

Dave

 

[Gryd3]

That does help.
Thank you Dave