How to Calculate the Length of a Conductor Using Resistivity

[@lsnogaming2893]

Wow you have GSH Electrical in a Joe Robinson Training video 👍. Great work lads you are changing Electrical training one video at a time 😀

[@oldgrunger5]

Awesome video Joe ...i was shown this onsite as an apprentice and was blown away how useful it was when fault finding on a ring final circuit 😎😎

[@oldgrunger5]

and lighting circuits too!!!

[@craigemmott4976]

Perfect timing. I have my science exam at 19.30 tonight! YOU SUPERSTARS!

[@djevil247]

How did you do Craig?

[@craigemmott4976]

Paul moss, not as well as I did 15 years ago, only a merit this time.

[@vievlogs589]

I love it, you had Gaz from GSH Electrical in your video Joe. ⭐️⭐️⭐️⭐️⭐️

[@pauldavies1693]

Hi Joe, another brilliant video, easy to understand and very interesting. One point, our College Lecturer and our course book says the resistivity of Copper is 17.5 x10-9. Does the difference matter? Thank you, you're a God send. Take care. 🤔❤

[@planetconker1104]

That's really cool. When I did my level 2 exams I was really struggling with resistivity, so I invented a formula to help me with it which I based around the idea of the voltage triangle. I couldn't do it as triangle, but I used a naughts and crosses table to take its place I called it the Parl Square. I actually have it on my own KZbin channel as I really like to share knowledge. If you watch it let me know what you think.

[@JoeRobinsonTraining]

That's a really interesting approach to transposing the resistivity formula! 👍🏼

[@watsond83]

Excellent, I remembered this from years ago!! Thanks for the refresher :-)

[@richardwash6678]

Yet again, super stuff!👍

[@JoeRobinsonTraining]

Thanks Richard, hope they're helping and keep watching for future content!

[@colinblythe3710]

Is there any way you can do this calculation WITHOUT a scientific calculator ???I was trying 0.19 x 1000 / 12.10 = 15.7m length0.19 Resistance12.10 resistance copper per meter OSG (table 11 /page 190)is this correct

[@AlanLumsden]

Great stuff Joe, and all for free!!! 👍

[@JoeRobinsonTraining]

Glad you enjoyed it.

[@earlyyearslearningisfun]

Wow Gaz from GSH Electrical 👍😀👏

[@stewben1169]

Brilliant video. Keep the maths simple

[@JoeRobinsonTraining]

Thanks Stewart, keep watching and feel free to suggest future content!

[@LocoSajoca]

Hey Joe, I have to say you have helped me with really understanding resistivity as trying to learn it through Microsoft teams with over 30 other students has been hard on the students but especially the teachers, so you have been a massive help - as has rapid Gaz 🙌👏👏 I do have a question though... I have a question that says - you have an immersion that has a current of 13A. Its wired by a twin cable with each Conductor csa of 2.5mm^2. The Conductors are copper and the resistivity is 1.72x10-8 ohm/m^3 and I need to calculate the maximum length of cable which may be used, if the cable voltage drop is not to exceed 11.5V. (this is not the volt drop used for cable selection). How do I solve this? I presume ohm's law for the resistance, then the resistivity formula. But I am not sure if I should half the answer as its a twin cable?

[@JoeRobinsonTraining]

Great question, watch this space.

[@iqbalkop2073]

A star delta is used in a 3 phase motor.The conductor from the star motor are wired 4mm2 copper conductors and have a resistance of 87.5mΩ. Using the resistivity of the cooper conductor to calculate the length of one of the live conductor of the starter motor. please help

[@gbelectricks]

Great video joe. Could you have used the r1 r2 table in the on site guide and obtained a value of 12.10 milliohms per meter for a 1.5mm2 copper conductor.. Then calculate the length of the conductor = measured resistance x 1000 then divide that by(m ohms/m)?? 0.19x1000 divide by 12.10 =15.70 meters??? Or am I missing something from the way I obtained my calculated value of length?

[@JoeRobinsonTraining]

No, that's absolutely spot on Gareth, great work. The reason we may have slightly different answers is the OSG uses a slightly different value for the resistivity of copper. I don't have on on me right now but off the top of my head I think its 18.1 milliohm metres. I'm not sure why but I would guess its something to do with standard requirements for the purity of copper or something. Great question, stay tuned for more!

[@carlitosdetamuin]

Great info bro. How can you measure the length of wire in different temperatures. What would be the math. Thanks in advance.

[@MomentsWithBrandon]

Hi Joe, need some help, How do I figure out the length of wire when you have no resistivity. In the question I have to answer, Im give the CSA, COPPER RESISTIVITY and a voltage drop please need some help understanding

[@mundent]

Can you help me out with this one. I'm still relatively newly qualified and trying to get my head around things. If you install a ring circuit of the max 100m then based on the table in the onsite guide, the resistivity of a 100m of 2.5 would be 100m x 19.51mΩ ÷ 1000 = 1.95 Ω. My questions are..... 1. How does that work if the max allowed impedance is 1.1Ω for 100m 2. If the answer is because impedence and resistivity are different things then is there a way to calculate the length of a cable from just the ZS. Thanks.

[@SO-fb4ef]

Very cool, but is measuring by hand still the most effective way?

[@JaykeSapalaran-iq3qs]

Great video information 👍❤ THANK YOU FOR SHARING YOUR KNOWLEDGE AND EXPERIENCE 🇵🇭🫡❤

[@JoeRobinsonTraining]

My pleasure! 😃

[@gbelectricks]

Hiya Joe, how could you modify this formula to carry out an R1+R2 calculation. So rather than a single csa measurement on 1 conductor? calculation it is say a 2.5mm/1.5mm t&e👍

[@Lacking_something]

Thank you! I went on a well known DIY forum, as I am testing a table lamp. I wanted to know the expected resistance of the cable so I could test it, i was told "as low as possible". I wanted to know the maths!!!

[@williammcintosh6006]

Joe, are you going to do any videos on transposing formulae?

[@JoeRobinsonTraining]

I'm planning on it Will, got lots in the pipeline!

[@williammcintosh6006]

@@JoeRobinsonTraining thanks!!!

[@SophieMazzier]

What happens if you are told you have a twin copper cable. Does that simply double the resistance?

[@danielteyehuago1633]

So please apart from the meggar what instrument can be used to measure the resistance of a cable

[@josealexgv]

Best regards. Could you help me to calculate the distance of a copper cable awg 10 using a multimeter Example I have a cable on a reel and the values shown by the multimeter in position 2k is .002 and in position 200ohms varies between 1.1 and 1.2 and continuity is .003. What would be the mathematical formula I should use to know the length of the cable. My knowledge in this area is not good, I am an apprentice.

[@jeremykemp3782]

Careful, I could lose count here. Brilliant, just brilliant. You can watch these vids more than once and still catch some funny bits that were missed on the first watch... Whilst learning at the same time,, You can't get better than that

[@joemoloney1067]

massive help thankyou but according to my book the resistivity value of copper is 17.5 which gave me 16.2m which was a bit closer.

[@stringsofbean1073]

Hi, I understand the video and the workings.. However, I'm currently stuck on a question that has me stumped a bit. The question is this : Approximately how long would a length of CPC be to give a reading of 0.36 ohms, considering that 1.5mm(2) has a resistance per metre of 12.1 Milli ohms? I don't know if/where the 12.1 should be substituted into the equation? Any help you can shed on to the subject would be amazing!!!

[@HidingZebraTube]

Thats your P value right??

[@anthonymiller880]

Joe✅

[@religiousblackman697]

Good vid

[@JoeRobinsonTraining]

Thanks!

[@sbmorris2k6]

I learned in college another way by using measured zs ÷ r1 +r2 value × 1000 to convert to meters

[@Dog-whisperer7494]

Clever bit of maths , but it’s to hard, the simplest way 0.19 ohms x1000= 190 milli ohms, 190 divided by 12.10 the factor from guidance notes 3 = 15.7 metres . Great video and useful for the number crunchers👍

[@reelsjury8095]

Hello sir i see your vd and you are a top master of science recently I had to find the length of cable we use for copper R= 0,0175ohm/m and 2,5mm2 for cable when I use this formula it's not fit. The cable length measured 215cm and Resistance measured 0,37ohm can you please help to find the correct length thanks

[@adelaidehulahoopers9286]

Funny guys! Good info.

[@W0KNI]

Just can't seem to get this working ... I have 30' of CCS #18 insulated wire. The closest calculation I can get is 127'. Using a multi-meter I get 0.5 Ohms resistance. The diameter of the wire is 0.05 inches or 1.27mm. Convert this to 1.27x10-6 m^2. I'm using 1.64x10-9 for the Resistivity of CCS. Help?

[@JoeRobinsonTraining]

Hi Stephen, you need to use the cross sectional area of the conductor not the diameter, calculate the area and then use it in the formula. Any better?

[@W0KNI]

@@JoeRobinsonTraining Thanks for the reply Joe. So here goes again! L=RA over P. Where R=.05 Ohms A = (pi*r²) OR (3.14*0.025²) .025 is the radius of the diameter (0.05) in inches. A = 0.002 rounded up. Then A to metres² A = 5.08*10^-9 m². P = 1.64x10^-6 L = not even close! LOL.

[@W0KNI]

@@JoeRobinsonTraining BTW - I went here to check my Area calc. www.sengpielaudio.com/calculator-cross-section.htm and it seems correct.

[@JoeRobinsonTraining]

Did you use 0.5 ohms or 0.05 ohms?

[@W0KNI]

@@JoeRobinsonTraining Sorry, typo. I used 0.5 ohms and got 15.49 m (Wire measured to 9.144 m/30.0 ft) R = 0.5 Ohms A = 0.0000508 m² P = 0.00000164 (Copper Clad Steele, 18# 19-strand.) L = 15.49 m

[@manuellastrollo2168]

what is the AWG of 1.5mm sq?

[@tfcekiso3045]

The units are ohm M that's for extra mark ❤️

[@timothylyons7399]

That’s some clever maths.

[@JoeRobinsonTraining]

Cheers Tim. Keep watching!

[@craigemmott4976]

Got through it but typical city and guilds, exam related to next to nothing in their own worksheets? WHAT’S THAT ALL ABOUT C&G?

[@JoeRobinsonTraining]

Glad you crushed it Craig, always challenging guessing what's in the examiner's head!

[@craigemmott4976]

Joe Robinson Training I crushed to a certain degree. A merit. Not as good I did 15 years ago.

[@JoeRobinsonTraining]

It's always the toughest exam Craig so don't sweat it, a merit's a great result for that assessment. Hope you're going to keep watching despite passing the principles!

[@craigemmott4976]

Joe Robinson Training will always keep watching, the information from your video are invaluable. You are always learning in this industry. I don’t profess to know everything and this one is very true after 15 years, if you don’t use it, you lose it.

[@ReSV1]

I tried to use your formula to calculate length. (To find the total cable routine underground and cable fault) The problem is, when I calculate it out, the length is a huge difference from what is shown on my Autocad data i had on hand. Which i don't get how i got it wrong. The cable is 3C x 185mm2. The total resistance (I connect the end-point at B to form a loop back to A, together [in essence, 2xL]) is 0.2 Ohm The length I calculated out is 1084m. However, the length on my Autocad data is sitting at a whopping 440m, which i can't figure out why

[@JoeRobinsonTraining]

That is a bit weird. 🤔 Where did the 0.2 ohms come from?

[@ReSV1]

@@JoeRobinsonTraining I got the value of 0.2 Ohm using a multi-meter that measure resistance.

[@JoeRobinsonTraining]

OK, was it a multi-function tester like a Megger or a multi-meter? The only reason I ask is that if it wasn't properly calibrated or not zeroed it could give a false reading and even a small amount of difference on the meter will have a fairly big impact on the result.

[@ReSV1]

@@JoeRobinsonTraining It is Megger brand. Calibration date of expiry is 21/8/2021

[@JoeRobinsonTraining]

Hm, well in that case I'm stumped, not sure why it would give you such a high value. 🤔

[@connordickens2617]

👍👍

[@georgereynolds124]

👍🏼👍🏼

[@koarivera9151]

Row ??

[@JoeRobinsonTraining]

The playlist and the video below should help. 😊 Resistance and Resistivity: kzbin.info/aero/PL7eNzIRgKe07asenaJfPBTtUwKGjMSadR

[@JoeRobinsonTraining]

kzbin.info/www/bejne/emSmo4x4jN6Vftk

[@uksuperrascal]

OK Joe there has been a sun spot magnetic flare and every IC in the world has been fried . Now do the sum with out a calculator in long hand explaining every step?

[@JoeRobinsonTraining]

😂 Are slide rules still operating?

[@uksuperrascal]

@@JoeRobinsonTraining Yes

[@Dog-whisperer7494]

In the real world No one is going to mess around with this kind of maths when the a much simpler way of doing it. Unless you’re a 70year old boffin 😂

[@Caducus40K]

Would it not be easier to express the value of p in microhms per meter rather then millimetres. that way its just (0.19*1.5)/0.0172 and you only have to do 17.2/1000. no need for a scientific calculator and you don't have to remember which values you have to x10^-6 or -9

[@gino2465]

Guys don't suppose you know the resistivity of 4mm and 6mm solar PV cable please

[@Noice-nater445]

I’m not tripping right now did he say that the resistivity of copper is 17.2x10to the minus nine?!. Wasn’t it 1.72x10to the minus 8?! Am I stupid or something to not notice something obvious

[@JoeRobinsonTraining]

Those two figures actually represent the same quantity of resistivity. 😃

[@leoleorelated]

😂😂😂😂

[@JoeRobinsonTraining]

Thanks Leo.

[@connordickens2617]

👍👍

[@rajuahamad6876]

Meaning of "p"