VOLTAGE DROP FORMULA Which formula to use and how to do the calculations correctly.

[@learnelectrics4402]

SEE ALL - To view a list of all our LearnElectrics videos, click on the link below. There are many videos on many electrical topics including Installation, Part P, 18th Edition, Testing, Certification, Lighting, Sockets, Ring Circuits and much more. kzbin.info/door/YaJQnpO4XAp0yCgqzMkmfA

[@grantrodgers2829]

learning the alternative calculation for unknown lengths / wire gauge has helped immensely. Thank you

[@learnelectrics4402]

Yes Grant, that's a good one. It came in very useful on periodic inspections over the years. Not a lot of folks know about it. Glad you're enjoying the videos. The video link below was the first video I published, this has an interesting "Trick Number" in it that you might like. Thanks for watching, appreciated. Dave. 35 is the Magic Number kzbin.info/www/bejne/i4OldWeiobGIbLs

[@musangobi2079]

Good explanation, now I will ever get confused about voltage drop

[@learnelectrics4402]

Glad we could help. Practice the formulas and you will have a skill for life. Bux.

[@sophiaenright1583]

this is so helpful for my electrical engineering exam, thank you sir! very well explained :)

[@learnelectrics4402]

So glad we can help Sophia. Lots more videos on our channel and lots more to come. Good luck with the exam. Dave.

[@maal491]

This video is so helpful, better then my actual book itself , thanks 🙏

[@learnelectrics4402]

Excellent, thanks for the very positive feedback and so glad we can help. Lots more videos to come. Bux

[@GarethPritchard-o1p]

Great video! Finally understand this. Now off to search your channel for a video on correction factors.

[@learnelectrics4402]

Glad it was helpful Gareth. The correction factor video has just been put on the list to be done, thanks for the nudge. But there are still lots for you to look at, thanks for the support, Dave.

[@u.a3185]

Best teaching method I ever seen .thank you sir !

[@learnelectrics4402]

Wow. Thanks for the great feedback Usman. Really appreciated and thanks for watching.

[@seandempsey9396]

Fabulous I hated learning this when I was at college, but it is so important that we do learn it, fabulous video as always. Thank you

[@learnelectrics4402]

Thanks for the good comments Sean. You can also read this on our website at www.LearnElectrics.com We are in the process of uploading written articles to the website for all the previous videos. It will take time but we will get there. Thanks again Sean Bux

[@tilidie5272]

youve helped me so much this channel is priceless to me!

[@learnelectrics4402]

Excellent, if it is helping it is doing its job. Thanks for watching, spread the word. Dave.

[@Dr.Stacker]

Is load always assumed to be at the end of the full circuit length? In a circuit with fixed loads such as a lighting radial, will the loads not be at different points/lengths from the CU and mean that we have to calculate vd at each individual point? Lastly in a domestic situation its unlikely all lights will be on at the same time. are there any diversity calculations to account for or do we always assume worst case?

[@learnelectrics4402]

See previous answer, thanks.

[@drpantastic1969]

Question does how a cable is installed affect the calculation say for cable sizing for example

[@learnelectrics4402]

Yes it does, we will be putting out an updated video on this soon. Dave.

[@Ramesh-nc7xw]

If i am calculating voltage drop for a lighting circuit do i use the measured length of the cable from the distribution board to the furthest light fitting or do i need to multiply that value by 2 seeing as the current has to travel back to the distribution board.

[@learnelectrics4402]

take a look at this latest video we've made on voltage drop, it will give you more information. But to answer your question, only measure the distance one way, from the CU to the point of use, NOT there and back. dave. kzbin.info/www/bejne/pIe9lnx8mqqqopI

[@Dr.Stacker]

Good question, I think the tabulated values for voltage drop per amp per meter in table two account for both the line and neutral wires and therefore you dont multiply by 2

[@adaliqbal6972]

I have been following your Videos and they have been very helpful to me as i can often have learning difficulties in classroom environments. They have been more helpful than ever before as my fulltime work is conflicting with the college classes at the moment and I am trying to play catch-up with Revision. 1st time leaving a comment and I felt the need to do so as the videos have been fast and informative and very understandable. I am a level 3 electrical installations student. Your work is a massive help with the theoretical aspects of the course. Appreciate the references to the onsite guide and also the Worked examples.

[@learnelectrics4402]

That's great news and so happy they are helping. Keep watching, lots more to come and do spread the word about the channel at college, there might be others struggling too. Dave.

[@adaliqbal6972]

@@learnelectrics4402 Good Idea will do that definitely.

[@donalfinn4205]

Much better than any book!👍☘️

[@learnelectrics4402]

Well thank you very much Donal. Your comment means so much. Really appreciated. Dave.

[@mrpoo7651]

This is very well explained. Helped me a lot. Thank-you so much sir

[@learnelectrics4402]

You are most welcome, thanks for watching. Dave.

[@sanbucaone]

Thank you, very well explained. Found it interesting to have alternative methods of obtaining vd. Keep up the excellent videos.

[@learnelectrics4402]

Glad you liked the video, your feedback is appreciated. Most colleges only teach you the minimum. We like to teach you what you need to know to be good at your job. Practice a few made up circuits and you will have a skill for life. Bux.

[@peterhorsell5186]

Great video, very helpful thank you. 1 question though - if looking to extend an existing circuit, do I need add the total maximum of all consumers on the circuit and calculate length of cable, to be able to work the figures out and check if the proposed additions would comply? Thanks

[@learnelectrics4402]

Yes, any extension to the circuit will increase the resistance in the circuit and increase the volts drop. Having said that, if the Vd was just 5 volts, say, for a 15 metre socket circuit and you were extending by perhaps only 3 metres, it is clear that the extra 3 metres will not take you over the 11.5 volt limit. Hope this helps. Bux.

[@joelgobeh7343]

Superb!!! You just make serious topics look easy.🙌🏾🙌🏾👏👏

[@learnelectrics4402]

Thank you so much Joel. What fantastic feedback. You've made my day. Dave.

[@antoniogalluccio4213]

The best video on KZbin regarding the topic and more complete of the others. Thanks for sharing this info with everyone, it is really helping out towards the 203 mock exam level 2. 11.5 volts permitted comes out of 5% of 230 volts right?

[@learnelectrics4402]

Absolutely right Antonio. You've got it. Thanks for watching, lots more to come. Dave.

[@gino2465]

Good morning quick question on a previous video you had some handy formulas my question is the formula was for 230 v what is differant if it's 3 phase 400v

[@learnelectrics4402]

Thanks Gino, someone else asked about 3 phase voltage drop so it must be time to do a video. Thanks for asking, its now on the list. Dave.

[@IftikharAhmed-lk5yk]

Excellent Videos, thank you very much. ONE QUERY PLEASE: voltage drop for single strand wire is 44mv per 1mm"csa per 1metre length, (my understanding) and for 2.5mm" wire voltage drop is 44/2.5 = 17.6mv per metre In this example we have 2.5mm" T&E 25 metres long ie 25 metres live wire and 25 metres neutral wire. So when calculating voltage drop for 25 metre long cable, the total length of current carrying wire is 25 m live and 25 m neutral = 50 meters. Voltage drop (milli volts) = (44 mv X 20 amps X 50m length) / 2.5 = 17600 mv = 17.6 Volts. This is what I Understand, please look into this as there is lot of confusion. Its same for cable resistance. 19 m ohms / 1mm" csa / 1m length for one wire only.

[@learnelectrics4402]

I'm quoting from Guidance Note 3 and the Wiring Regulations which rounds the numbers up or down to whole numbers. On an average run length of cable it will only make a tiny difference. Thanks for watching. Dave.

[@IftikharAhmed-lk5yk]

@@learnelectrics4402 Thank you for for quick reply. my point was there are 2 wires (live and neutral) each 25 metre long, so when calculating voltage drop total length of wire will be 25 + 25 ie 50 meters. So when calculating voltage drop in one 25 metre long strand = (18 X 20 X 25 ) / 1000 = 9 VOLTS and in 2 strand (live + neutral) voltage drop will be double, ie 18 volts. Table 2 / 4d1 (single) states voltage drop is 18 mV for 2.5mm" csa per metre.

[@ibrahimmustafa2902]

Do we calculate the length with 2 for single phase load ?

[@learnelectrics4402]

This is the single phase formula and takes account of there and back i.e. line and neutral. We just measure the distance one way and the formula does the rest.

[@robertwainwright5441]

Another great video 👍

[@learnelectrics4402]

Glad you enjoyed it. Thank you.

[@Hossin-x3i]

You are the best ..thanks alot very useful

[@learnelectrics4402]

You are welcome, thank you.

[@gino2465]

Hi I have tried this using the tables in osg to compare, it's very close to 2.5 wire but say not with 16mm cable using the majic 1.2 factor

[@learnelectrics4402]

The OSG rounds up/down the figures so there will always be tiny differences.

[@azizullahkhan7888]

Thanks for uploading informative clips

[@learnelectrics4402]

It's my pleasure, glad you enjoy them. Lots more to come.

[@echenduconfidence4998]

Thanks sir for the great video. Pls what is the name of the reference book you use in this video.

[@learnelectrics4402]

Thanks for the comments. All the information is in the Wiring Regulations and the On-site Guide. BUT - There is more information in the video than in the books, I have added to what you will find in the books. Dave.

[@AndrewCook7]

Great Dave thanks. Why do we not use 50 mtrs for a 25mtr length. We have phase and neutral, 2 length of cable. Always wondered why the length is from the source to the appliance and not the return as well

[@learnelectrics4402]

The voltage drop calculations that the boffins give us have included the phase and neutral paths. Hope this helps. Dave.

[@colinblanchard2828]

This has been very helpful, thanks

[@learnelectrics4402]

Glad to hear it, thank you.

[@ranjan1436]

very nice, you make things look so easy? thanks very much.

[@learnelectrics4402]

So glad we could help Swapan. Thanks for watching. Dave.

[@Gandalf4137]

How would the equation change if we used an aluminum conductor instead? I believe its mV/a/m rating would be different, no? Thank you.

[@learnelectrics4402]

Yes, the data would change. Every material and mix of alloys has its own data table. For Aluminium cables have a look on page 479 in the brown Regs book. Thanks for the support. Dave.

[@alextaramsari]

Another well explained video!! THANK YOU!!!

[@learnelectrics4402]

So happy you appreciate it. Your comments really make the effort worthwhile. Thanks. Bux.

[@tww5719]

Where does the formula of how the cable is run,and the thermal conditions come in towards the final volt drop eguation xx

[@learnelectrics4402]

You should calculate the cable installation conditions and thermal conditions first to determine a minimum size and then the voltage drop to check that the size selected is ok. Hope this helps, it can be tricky sometimes deciding which is the best order. Dave.

[@tww5719]

@@learnelectrics4402 yes thanks,must admit a lot of electricians take things for granted without working out the volt drop,when I did the 17th update the lecturer was hot with volt drop,he gave us a sample for a 10kw shower in a house ,no great run and nothing special,it come out as the minimum of 16mm,everyone was shocked so to speak,I told him the manufactures had better make bigger switches to take a 16mm,I mainly do industrial work which is a different kettle of fish and working out voltage drop is a must 👍

[@gregmcallister4862]

Very informative, and great content

[@learnelectrics4402]

Thanks for watching Greg.

[@sanbucaone]

Evening just revisiting voltage drop.😁 with regards to voltage drop when the load is unknown ie a summer house with three double sockets. And it’s unknown what client would plug in. Would we use the Breaker size at the board as Ib? I guess my question is if ib unknown do we use the breaker size to carry out the formula. Many thanks.

[@learnelectrics4402]

Absolutely. Yes, us the rating of the breaker as your Ib. Thanks for watching. Dave.

[@michaelcostello6991]

The first method used the length of cable and the second method used double this value ie live and neutral lengths added. Do we need to understand why is this or is it something we should accept. Thank you for great video

[@learnelectrics4402]

Michael, method 1 is when you know the cable sizes, lengths and (mV/A/m). Method two is when you have two ends sticking out of the wall, no real idea of length, size debatable and no chance on (mV/A/m). All you know is the load of the attached equipment. Typical when inspecting and testing some properties or factories. Method 1 you will need for 18th exam. Method 2 will give you the skill to work volts drop out on site when everybody else says it is impossible. Learn both, look good. Hope this helps. Dave.

[@natarmstrong8931]

Struggling to find the voltage drop equation for a ring main circuit.....any help would be appreciated.

[@learnelectrics4402]

Good one Nat, there are lots of variations for working this out. Good news, Thursdays video is about Ring Circuit voltage drop. Hope you enjoy it. Dave.

[@hanzlaabbas2488]

Length is 25m is this only way or complete length of the cicruit from phase to neutral

[@learnelectrics4402]

The length from the CU to the point of use.

[@learnelectrics4402]

as below

[@mohammedborhan9677]

Hi, can you please send me the formula for voltage drop for socket three phase For single phase is 11,5 What is the formula for three phase Thank you

[@learnelectrics4402]

The tables, with all the different numbers for 3 phase are in Appendix 4 of the Brown Wiring Regs book. Thanks for watching.

[@dennisfowler7873]

Another great video .... been waiting for this for a while now...one question.... can both formulas use the 1.2 multiplying factor or is it just for the ( R1 + Rn) formula

[@learnelectrics4402]

Thanks Dennis. Only the R1+Rn calculation uses 1.2. The (mV/A/M) number in the standard formula has already allowed for temperature adjustment. Hope this helps. Bux.

[@Hossin-x3i]

Thanks alot very useful

[@learnelectrics4402]

Nice of you to say so, thank you.

[@gbelectricks]

Great video. On the last formula could you explain the 44 figure on the top row of the equation? Where does this come from and why is it always 44? Thanks 👍

[@learnelectrics4402]

44 is the reference figure that makes the equation work, it is the value for 1mm. Try it with the same values we have just used in the first example. 20 amps x 25m x 44 divided by (11.5 volts x 1000) gives 1.91mm minimum cable size and in the example we have chosen we have selected 2.5mm. Hope this helps. Bux.

[@sorbunsong6934]

sir , how can i download bs code for applying in electrical?

[@learnelectrics4402]

If you need the British Standards documents search Google for the BS number.

[@sorbunsong6934]

@@learnelectrics4402 but bs code is not for free sir

[@learnelectrics4402]

That's correct. All BS documents have to be paid for. There is nothing we can do about that, if it is needed you will need to buy it from BSI. Hope this helps.

[@icetin7568]

GREAT VIDEOES AGAIN MANY THANKS . Can you do more videos about inspection AND TESTING or EICR , SEQUENCE OF TEST . I CANT WAIT . ,MANY THANKS

[@learnelectrics4402]

Thanks for the great comments. Testing, certificates etc. are on the list and we will be doing videos on these very soon. Thanks for your patience and suggestions. Dave.

[@maal491]

@@learnelectrics4402 I am interested on that too, can't wait

[@learnelectrics4402]

Thanks, we will do this video very soon, meanwhile, enjoy the others. Glad you are finding them useful. Bux.

[@krazylad84]

excellent stuff, thanks !

[@learnelectrics4402]

Thank you for the positive comment, appreciated.

[@mohammedborhan9677]

Hi teacher could you please give us example for cable calculation for three phase for one heater or cooker and second example for three phase also but we need to install 3 ovens every oven is 5.8kw alle these ovens in same cable and one circuit breaker. Thank you

[@learnelectrics4402]

Mohammed, we cannot give specific sizes for what you want as we haven't seen the installation and we do not know the installation conditions. Look at our video Breaker and Cable Sizes for Electrical Circuits kzbin.info/www/bejne/aZCnZ2hjaJerppo Thanks for watching

[@mohammedborhan9677]

@@learnelectrics4402 thank you for your response and if you can just one example for three phase cable calculation Thank you

[@learnelectrics4402]

We will be doing a video on three phase in the near future.

[@mohammedborhan9677]

@@learnelectrics4402 what is the reason we have higher measured earth loop impedance ? And what is consequence for that? Thank u

[@learnelectrics4402]

Usually poor circuit design in the first place or additions to circuits without recalculating. The consequences of high Zs could be that the breaker does not protect the customer properly and they die. Look at our video Zs too high kzbin.info/www/bejne/nIbPdHeeoch3nJY

[@rohulamin5353]

Can this work for ring final

[@learnelectrics4402]

Yes, have a look at our video Cable length calculations and R1+R2 on this link kzbin.info/www/bejne/h6LCaoCEfZ2Lrrc It covers ring and radial circuits. Thanks for watching

[@pah9844]

So I know I’m doing this right, can somebody help. If I look at the final formula question, min size of cable to not exceed VD. My own numbers made up below; 1b 3kw = 13amp L 44 vd 11.5. 13a x 44L 11.5vd x 1000 Do I have this right?

[@learnelectrics4402]

No, you've missed part of the formula out Paul. You have not included 44 for the mV/A/m standard value. the top row should be 13 x 44 x 44 and the bottom row 11.5 x 1000 This will give a cable size of 2.1mm minimum. You should choose 2.5mm cable. Hope this helps. Dave.

[@pah9844]

Just realised what I have done…. Misread the formula and put 44 as L.

[@patrickjacobsen7805]

So good.

[@learnelectrics4402]

Great feedback Patrick. Thank you. Dave.

[@DasTwigster]

brillant thanks

[@learnelectrics4402]

Glad it was useful, thanks for watching.

[@mprime1154]

Thank you Sir

[@learnelectrics4402]

Most welcome, thank you for watching. Dave.

[@IceyJunior]

mV/ A/ m isn't it the same as m\Ohm / m?

[@learnelectrics4402]

It is called mV/A/m in the regs book. Other industries might use a different abbreviation. Thanks for watching.

[@kdiddy4714]

Thank you

[@learnelectrics4402]

You are very welcome. Glad you found it useful. Bux.

[@alig7800]

THANK YOU

[@learnelectrics4402]

Glad you enjoyed them. Thanks. Dave.

[@HakensKenneth]

thanks

[@learnelectrics4402]

Your welcome, thanks for watching.

[@frog.n.toast2938]

7671 2sd amendment videos will be welcome !great job

[@learnelectrics4402]

We're already up to video 7 on 2nd amendment. Thanks. Dave.

[@maysasaeed7964]

ممتاز

[@learnelectrics4402]

Thanks for watching. Dave.

[@mikeadler434]

👍👍👍

[@learnelectrics4402]

Three thumbs, appreciated. Thanks for watching.

[@pah9844]

Could i pick your brain just the once more. My own cooker. Ib 4kw -4000w L 1m cable. mV/A/m is 6mm cable 7.3 mV/A/m (table 4d5) 7.3 x 17 x 1 ~~~~~~~~ 1000 0.12 amp drop Thanks.

[@learnelectrics4402]

Yep, that's almost correct Paul, it will be 0.12 VOLTS not amps - but is it really 1 metre from the consumer unit? If it was 10 metres from the Cu your Vd would be 1.2 volts Thanks for watching, lots more to learn. Dave.

[@pah9844]

@@learnelectrics4402 i was just making up a low number to see the difference.

[@timgean8954]

volume!!

[@learnelectrics4402]

Thanks Tim, thanks for watching. Dave.