Elecraft

Current Flow on Copper Strips - a Question

Classic

List

Threaded

4 messages Options

Edward A. Dauer

Current Flow on Copper Strips - a Question

Since I don't know what precedes the word "thus" in the quotation below I would ask if someone could explain this phenomenon for me.

I am trying to visualize this with a thought experiment. In an earlier post someone (Skip?) mentioned that early transmission lines were sometimes hollow copper tubes, to respect the fact that AC flows only on the outside of a conductor. So, imagine a hollow tube carrying RF (which may approximate the fast rise and fall times of a high voltage strike). Current is flowing all over the surface, I gather. Now squeeze the tube along its length so that a cross section becomes an ever flatter ellipse. At the last instant squeeze it so that the sides are in contact with each other. What happens to the current flow as that squeezing occurs? Is it still all around the squished tube until the instant the two sides join? And then it all flows primarily along the edges of the now flat conductor? Howcome?

Tnx,

Ted, KN1CBR

------------------------------

Message: 3
Date: Wed, 25 Apr 2018 18:45:39 -0700
From: Wes Stewart <[hidden email]>
To: [hidden email]
Subject: Re: [Elecraft] OT: Grounding Question
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=utf-8; format=flowed

Radio Engineering and Radio Engineer's Handbook are two different critters.? My
copy of Radio Engineering is the third edition and the pertinent information is
on p.20.

To partially quote: "Thus, with a flat-strip conductor, the current flows
primarily along the edges."

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Wes Stewart-2

Re: Current Flow on Copper Strips - a Question

"When skin effect is present, the current is always redistributed over the
conductor cross section in such a way as to make most of the current flow where
it is encircled by the smallest number of flux lines. This general principle
controls the distribution of current irrespective of the shape of the conductor
involved. Thus, with a flat strip conductor (figure reference not shown) the
current flows primarily along the edges, where it is surrounded by the smallest
amount of flux, and the true or effective resistance will be high because most
of the strip carries very little current. (A reference to the missing figure)
makes clear that it is not the amount of conductor surface that determines the
resistance to alternating current but rather the way in which the conductor
material is arranged."

On 4/26/2018 6:35 PM, Dauer, Edward wrote:

> Since I don't know what precedes the word "thus" in the quotation below I would ask if someone could explain this phenomenon for me.
>
> I am trying to visualize this with a thought experiment. In an earlier post someone (Skip?) mentioned that early transmission lines were sometimes hollow copper tubes, to respect the fact that AC flows only on the outside of a conductor. So, imagine a hollow tube carrying RF (which may approximate the fast rise and fall times of a high voltage strike). Current is flowing all over the surface, I gather. Now squeeze the tube along its length so that a cross section becomes an ever flatter ellipse. At the last instant squeeze it so that the sides are in contact with each other. What happens to the current flow as that squeezing occurs? Is it still all around the squished tube until the instant the two sides join? And then it all flows primarily along the edges of the now flat conductor? Howcome?
>
> Tnx,
>
> Ted, KN1CBR
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 25 Apr 2018 18:45:39 -0700
> From: Wes Stewart <[hidden email]>
> To: [hidden email]
> Subject: Re: [Elecraft] OT: Grounding Question
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Radio Engineering and Radio Engineer's Handbook are two different critters.? My
> copy of Radio Engineering is the third edition and the pertinent information is
> on p.20.
>
> To partially quote: "Thus, with a flat-strip conductor, the current flows
> primarily along the edges."
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

John Huggins, kx4o

Re: Current Flow on Copper Strips - a Question

In reply to this post by Edward A. Dauer

What's more appropriate for coaxial building entry grounding management?

This wide-strap, allegedly low inductance, approach...

https://www.comm-omni.com/polyweb/images/pb.jpg

...or this more R56 approach...

http://www.radio2way.net/MGB.jpg

?

73
John, kx4o

On Fri, April 27, 2018 02:21, Wes Stewart wrote:

> "When skin effect is present, the current is always redistributed over
> the conductor cross section in such a way as to make most of the current
> flow where it is encircled by the smallest number of flux lines.Â This
> general principle controls the distribution of current irrespective of the
> shape of the conductor involved. Thus, with a flat strip conductor (figure
> reference not shown) the current flows primarily along the edges, where it
> is surrounded by the smallest amount of flux, and the true or effective
> resistance will be high because most of the strip carries very little
> current.Â (A reference to the missing figure) makes clear that it is not
> the amount of conductor surface that determines the resistance to
> alternating current but rather the way in which the conductor material is
> arranged."
>
>

Martin Sole-3

Re: Current Flow on Copper Strips - a Question

I go for the Polyphaser approach. I have used and installed their PEEP
system on multiple sites here in Thailand. High exposed sites with a lot
of lightning. Notable over the 20 years since the first one was
installed there is significantly higher equipment reliability of
equipment at those sites and none of what were historically regarded as
"typical regular failures".

The PEEP system tries to keep any surge energy outside the building. I'm
a firm believer in not letting it inside any more than is absolutely
unavoidable. In a lot of cases once it gets in the building it is highly
unpredictable. Think 4 inch hole burned in pcb back plane, steel rack
cabinet door and vapourised wall mounted fire bell.

The whole sites have very good protection systems designed primarily
around FAA-019E standard, though I would agree with Polyphaser that some
of what is contained in that standard is not always ideal. A lot of
historical convention gets passed on unquestioned into some of these
standards over the years it would seem.

Regards
Martin, HS0ZED

On 27/04/2018 21:33, John Huggins, kx4o wrote:

> What's more appropriate for coaxial building entry grounding management?
>
> This wide-strap, allegedly low inductance, approach...
>
> https://www.comm-omni.com/polyweb/images/pb.jpg
>
> ...or this more R56 approach...
>
> http://www.radio2way.net/MGB.jpg
>
> ?
>
> 73
> John, kx4o
>
> On Fri, April 27, 2018 02:21, Wes Stewart wrote:
>> "When skin effect is present, the current is always redistributed over
>> the conductor cross section in such a way as to make most of the current
>> flow where it is encircled by the smallest number of flux lines.Â This
>> general principle controls the distribution of current irrespective of the
>> shape of the conductor involved. Thus, with a flat strip conductor (figure
>> reference not shown) the current flows primarily along the edges, where it
>> is surrounded by the smallest amount of flux, and the true or effective
>> resistance will be high because most of the strip carries very little
>> current.Â (A reference to the missing figure) makes clear that it is not
>> the amount of conductor surface that determines the resistance to
>> alternating current but rather the way in which the conductor material is
>> arranged."
>>
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]