Calculating Copper Wire Resistance for Less than 500mohm; Cable Length 15m, Min Cross-Section 25mm

Hello, I counted but it doesn't work out, I need to count what cable (copper) to buy so that its resistance is less than 500mohm, The length of the cable is 15m, and the minimum cross-section is 25mm. Otherwise, what cross-section must this cable have for a length of 15m to have a resistance of less than 500mohm

Regards

Here are the calculation formulas with examples:
http://fizyka.biz/prad_elektryczny_002.html (in the link they give a different resistance for copper, 0.01534 instead of 0.017, which I know).

The resistance of 1 m of copper wire (or strand) with a cross-section of 1 mm2 is 0.017 ohms (17 milliohms). 15 m of such a wire (or strand) has a resistance of 15 × 0.017 = 0.225 ohms, or 225 milliohms.
Since your limit is 500 milliohms (0.5 ohms), so you can use a wire with a cross section of 0.5 mm2, then its resistance will be 450 milliohms.
A cross section of 25 mm2 is unnecessarily 50 times TOO LARGE, so instead of < 500 milliohms you will have < 10 milliohms.
Is it clear now?

Copper resistance is 0.017 Ω*mm2/m. From this you can easily calculate the resistance of a cable of any length.

who calculates from such formulas, the reciprocal of the specific resistance is conductance and ranges from 54 to 56 (easy to remember and small errors) R = l / 54 * s to get 150mohm, the cross-section is 1.8 so we take the nearest up normalized 2.5

Added after 2 [minutes]:

for 500mohm it is 0.55 or 1mm and what is it needed for voltage drops or what?

egon151!

you messed up a little bro...
A wire with a cross-section of 1 mm2 (not diameter or radius!) over a length of 1 m has a resistance of 0.017 Ω - we all agree on that.
15 m of such a wire has a resistance 15 times greater, i.e. 15 x 0.017 Ω = 0.225 Ω (in other words: 225 milliohms).
Our colleague wants less than 500 m #937; (not 150 mΩ!), which allows for MORE resistance, which means that you can give a LESS cross-section. A cross section 2 times smaller (i.e. 0.5 mm2) will give a resistance twice as large, i.e. not 0.225 Ω, but 0.45 Ω, which is less than 0.5 Ω - the condition is met.
Your result: " for 500 mom it is 0.55 or 1 mm " has nothing to do with it: where does 0.55 - what? - a millimeter come from diameter , Whether section ? - and then - this 1 mm - also what? And where did the result of 1.8 or 2.5 come from - also what? It is about mm Whether mm2 ?

peszkoit wrote:

Hello, I counted but it doesn't work out, I need to count what cable (copper) to buy so that its resistance is less than 500mohm, The length of the cable is 15m, and the minimum cross-section is 25mm. Otherwise, what cross-section must this cable have for a length of 15m to have a resistance of less than 500mohm

Regards

Physics formulas are about calculating the resistance of a wire, not a cable. When it comes to links, the matter requires knowing the number of wires included in it and their diameter. As I have been in the industry for 45 years, I have not seen anyone counting something like that, it is rather measured in the factory, e.g. a (factory) section on a spool, e.g. 1km, and then converts the resistance to a meter.
If the manufacturer gives the cross-section of the cable, it is only an approximate value. So if you count the cross-section of a round wire and then buy a cable with the same or larger cross-section