## Copper wire resistance

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I'm knocking up a spreadsheet to calculate cable resitance, at times one needs this stuff as brain gets older.

My old TAFE book tells me it is 1.72x10-8 Ohms per metre at 20 deg. C, and it seems to have comfirmation from Google, however I have also found a site which claims it to be 1.678x10-8 Ohms per metre at 20 deg. C but it says also for high purity stuff.

Not much of a difference but it MAY make a difference at high currents.

Any thoughts?

I have also found out that I have been robbed for years from cable manufacturers who claim that 7/0.50 cable is 1.5mm2 when it is infact 1.3744mm2 if I got my mumbers right...I'll have to sue!

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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So it seems that 1.72x10-8 Ohms is for annealed copper and 1.678x10-8 Ohms is for copper according to Wikipedia.

My book did say annealed copper now that I look carefully.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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What size wire? .0172 Micro Ohms per meter? Are you sure about this?

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Quote:
What size wire?
The "standard" resistance is given for 1m of wire which is 1m x 1m in size, I didn't make the rules. :-)

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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do you also keep in mind solid and strained(?) copper wires? as they also might have different conductivity ratings.....

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RickB wrote:
What size wire? .0172 Micro Ohms per meter? Are you sure about this?

this is if your wire has a diameter with a surface of 1m2

r= P*l/A

P= resistivity
l = length of cable
A = surface

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Quote:
do you also keep in mind solid and strained(?) copper wires?
I put in a formula which can accept number of strands and diameter size which is then converted to square mm for the formula.

Seems to be close enough to other examples I have found on the net. One thread mentioned the resistance as 1.724x10-8 others use 1.7x10-8.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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John could you provide to us the spreadsheet?
Or does anyone know an spreasheet for it? Coooper and aluminium?

Regards,

Bruno Muswieck

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Copper work hardens easily, so do not bend. :)

It all starts with a mental vision.

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Brings to mind the Admiral Grace Hopper thingy "how long is a nanosecond"?
http://en.wikipedia.org/wiki/Gra...

Quote:
Grace Hopper is famous for her nanoseconds visual aid. People (such as generals and admirals) used to ask her why satellite communication took so long. She started handing out pieces of wire which were just under one foot long (11.80 inches), which is the distance that light travels in one nanosecond. She gave these pieces of wire the metonym "nanoseconds."[28] She was careful to tell her audience that the length of her nanoseconds was actually the maximum speed the signals would travel in a vacuum, and that signals would travel more slowly through the actual wires that were her teaching aids. Later she used the same pieces of wire to illustrate why computers had to be small to be fast. At many of her talks and visits, she handed out "nanoseconds" to everyone in the audience, contrasting them with a coil of wire nearly a thousand feet long, representing a microsecond. Later, while giving these lectures while working for DEC, she passed out packets of pepper which she called picoseconds.[29]

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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OP wrote:
1.72x10-8 Ohms per metre

I do not want to be picky but where did you get that notation from? I think "1.72e-8" is the standard one.

Besides it is not "ohms per meter". IIRC "ohm metres" [ohm*m] is the unit of specific resistance.

And w.r.t. the value itself - it is about the same up here.

OP wrote:
I have also found out that I have been robbed for years from cable manufacturers

Steel is about 30 times cheaper than Cu and has only about 4 times worse specific resistance per mass (gives a ratio of 6:1 per \$).
If you are concerned - treat it as a hint :)

EDIT: metres not meters! Thanks.

No RSTDISBL, no fun!

Last Edited: Mon. Feb 18, 2013 - 05:23 PM
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Quote:

IIRC "ohm meters" [ohm*m] is the unit of specific resistance.

I always use an "ohm meter" to >>measure<< resistance. :twisted:

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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js wrote:
Quote:
What size wire?
The "standard" resistance is given for 1m of wire which is 1m x 1m in size, I didn't make the rules. :-)
Isn't that a cube, not a wire?

Smiley

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http://library.bldrdoc.gov/docs/...
is a scan of U.S. National Bureau of Standards Handbook 100 February 21, 1966

An interesting quick read, if nothing else. ;)

On one of the first pages is

Quote:
One of the advantages of
this particular value is that in terms of volume
conductivity it is an exact whole number, viz,

58 meter/ohm-mm[squared] at 20 degrees C

So I took that number, and went to Table 5 with all the AWG numbers and various parameters of each. 17 gage is pretty close to 1 square mm in cross section. Doing the calculation using the 58 from above gave very close to the table value. Similarly with 7 gage, fairly close to 10 square mm cross section.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Brutte wrote:
OP wrote:
1.72x10-8 Ohms per metre

I do not want to be picky but where did you get that notation from? I think "1.72e-8" is the standard one.

1.72x10-8 is a perfectly valid and common scientific notation, if you use superscript for the exponent. Unfortunately superscript seems to be unsupported on this forum :(

The E form is commonly used on system that cannot handle superscript, like calculators and computers.

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One of the online calculator I found http://www.chemandy.com/calculat...
and the one I put together. In typical M\$ style the file size goes from 6K with the original MS Works2000, becomes 12K with Xcel 2000 and bloats to 26K with the latest Xcel (evaluation version which came with my laptop), all to do the exact same thing. :(

## Attachment(s):

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Quote:
1.72x10-8 is a perfectly valid and common scientific notation, if you use superscript for the exponent.

You are right, I didn't notice that.
I thought that this is it - a complete notation style I have never seen before.

No RSTDISBL, no fun!

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...and to be picky e stands for natural log.. :wink: anyway M\$ Works and excel like to use ^ for exponential as in (1.72*( 10^-8 )), I had to use ^2 for square as I can't remember the correct way of doing that.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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So at milliamp levels on a 2 inch PCB, it's not worth thinking about. Unless, of course, you're talking *10^(a big exponent) milliamps.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut.

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In this post there have been lots of references to ohms per meter.
The actual "dimension" of resistivity (rho) is ohm x cm or ohm x meter.

When I was teaching at a TAFE for a while, we used to get students to do lots of calculations to hone their math & calculator skills. Now with js's spreadsheet, the following generations will be dumbed down even more! :lol: If it can't be done with a PC, it can't be done! :cry:

Whilst on the matter of dumbing down ( here comes the hi-jack) , I can remember when I was at school Australia had committed to buying F111's. They seemed to take ages and there was a huge cost blowout. Fifty years later, we seem to be in a similar situation, where Australia have some how committed to the F35 JSF and the delivery & cost blowout will be several orders greater.
I wonder if this is due to the dumbing down in society?
I wonder if the JSF will ever happen?
I gather that many countries are now reneging on their initial commitment to buy, especially since the new Russian & Chinese fighters are out performing it in flying & stealth performance rather then in smarts!
It is ironic that the F35 Lightning II can't fly during lightning conditions.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

Last Edited: Tue. Feb 19, 2013 - 10:09 PM
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Or idiots like me will continue to figure it out 'cause they can't find JS's spreadsheet

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut.

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I'm not the only one to blame! :lol: my TAFE text book mentioned above even gave a few examples of BASIC and PASCAL code to solve some problems.

And it's good that "the following generations will be dumbed down even more!" more employement oportunities for me. :lol:

I have been helping out son and son in law with 12V garden lights and wanted to make sure that the wire was heavy enough so as not to drop too many volts.

You only get a choice of 2 wire sizes at Bunnings for that and of course I went for the thickest to be sure to be sure...

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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But don't forget, to halve the diameter & use the radius for calculating the cross sectional area. I would like a dollar for every time I have said that! :lol:

If the garden lighting uses LEDS, some resistance would help in the ballasting John!

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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I think you're overengineering the garden lighting ;)

But don't use those insulation displacement taps. They're terrible.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut.

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Quote:
halve the diameter & use the radius for calculating the cross sectional area
That's the way I remembered it from school but the formula was in Italian so I decided to use the English version from the book. :mrgreen:

The lights are 5W quartz, and one loop (20m??) had quite a few lights on it.

To reduce voltage drop we fed the loop from both ends, unfortunately my son in law reversed the wiring in one of the lampholders so the lamps were pretty bright near the transformer but almost off near the maibox...and the ground was getting hot..all is well now. :-)

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly