EASY VOLTAGE DROP FORMULA and CABLE SIZE CALCULATIONS - ALL IN ONE - NO BOOKS - NO TABLES
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- čas přidán 9. 07. 2024
- We’ve been asked by many times if the voltage drop formulas can be made any easier.
Some say that the tables just confuse them, there is too much going backwards and forwards in the book and so on.
So what we will do in this video is what is called formula manipulation.
We will show you how to combine some different formulas that we might already know into just one formula that works better for us and is easier to use. Especially as this method uses no books or tables.
Everything is self-contained within the formula that we show you.
This video is No.126 on our CZcams channel where we have videos on a wide range of electrical topics.
To see a full list of all our LearnElectrics videos, click on the link below.
/ @learnelectrics4402
You can also view all our videos by typing LearnElectrics all one word into the CZcams search bar.
Always work safely, electricity can be dangerous. If you are unsure, stop and seek advice.
This video is provided for guidance only. Every electrical situation is different, please check and ensure that you are applying this learning information to your own individual circumstances correctly and safely. If in doubt, stop and seek competent advice.
I’ve been in the trade for 26 years, and this is a regulation!!! Never seen this before 🤷♂️
Thanks for sharing your knowledge Dave😁👍
You wouldn't normally do this on initial verification for new circuits if they have been properly designed. Useful to check extensions and DIY disasters on periodic inspections. Thanks for watching. Dave.
@@learnelectrics4402 great video. I just read back my comment! I meant to say, this is a revelation!!
Thanks again😁👍
This back pocket maths beats the complicating scholars at the IET. Brilliant 😉
Back pocket maths. I like it. Thanks for the support. Dave.
Hear hear
Been on an adult course to become an electrician for over a year now, how and why have I not found you before? Brilliant resource, definitely subscribed and will now be watching all your vids, thank you so much
Thank you Nicole and thanks for watching. Great feedback, and now that you've found the channel and the website make the most of it. Stay with it, it's a good trade to be in and it's taken me around the world several times. Good electricians are always needed. Dave.
Thank you LearnElectrics for the continuous value creation. Very helpful resources
Thanks for the great feedback, appreciated. Dave.
The lecturer is brilliant as he clearly explained step by step, worth watching, super understandable and highly recommended!☝😃❤
Great feedback, appreciated, thanks for watching. Dave.
Ever so grateful indeed. Ornamental!
Absolutely cracking 👏 how i wish i knew this channel 4 years ago when I was in college, its could have made my life much more easier. Keep it up
Thanks for the great comments and yes, I wish there was CZcams back in the 70s when I was training. Dave.
In preparation for my BS7909 exam, I was up at 1.15 this morning, watching this presentation. Absolutely superb. Made complete sense of the voltage drop calculation and, at a stroke, turned the entire calculation process into a thing of beauty, in it's simplicity with this new approach to solving the problem. Thank you to all those involved.
Brilliant response, thank you. If it helped then the video has done its job. Good luck in your exams. Dave.
A Brilliant resource broken down to something I can finally understand, a cracking channel Thankyou for your content!! 👍😄
Great feedback Tom. Dave.
Cant thank you enough for this knowledgeable explanation ..Didnt learn all this in 3 long weeks of virtual lesson than what i learned in 16 minutes.Really appreciated
Great to hear that. Much appreciated, lots more to come.
Hi Dave. I would just like to take this opportunity to say that you are a genius. This video has helped make life so much easier when trying to work out voltage drop and for aiding in the selection of cable size. I have been experimenting by using different figures in the calculations (ie. Cable length and Power rating) to see how much leeway one would have before having to increase cable size (CSA). This also gives you an idea of the load tolerance the cable selected would be capable of. Thank you again for making these videos.👍👌
Chris, you are doing exactly what I have done over the years. Experiment and find out, try different calculations etc. I'm a great believer in "WHAT IF?" and then finding out. keep learning, good luck. Dave.
I iterate the below, just about to sit my 2391-52, choose an online course provider and struggled to get explanations of calcs from them. Fantastic resource you are providing, well delivered. It seems so simple!
Thanks for the positive comments, appreciated. Glad you found the videos useful. Dave.
This is great, thank you for sharing really appreciate it!!
My pleasure my friend. Glad it was useful. Dave.
Thank you.
That's the best and only video anyone needs to understa d voltage drop calculations!!
Wow, great feedback, thank you. Dave.
Usual great stuff Dave. Thank you.
Glad you enjoyed it Mark, thanks for the support on the channel. Dave.
Wow now really make sense! Thank you very much!
Great feedback, thanks for watching. Dave.
This is eplained so clearly and all of these videos are such a great help to me ,thank you!
Glad it was helpful, thanks for watching. Dave.
That's absolutely very helpful and very useful thank you
Great to know that Abdul, thanks for watching. Dave.
So easy to understand your explanations Dave!
Brilliant!
Regards mg.
Many thanks, great comments and thank you for watching. Dave.
Brilliant! Needed to run some cable for a piece of equipment in my workshop, and this video was very helpful, thank you!
That's good to know it helped, thanks for watching, appreciated. Dave.
Wow! This is very informative, thanks for sharing it with us Dave. It worth it and the best tutorial on the topic for me.
Glad it was helpful. Dave.
@@learnelectrics440210:01
Urgent attention needed at 10:07. When you apply the voltage drop method for determining the cable size of the 6Kw heater you had 4mm² but when you use the cable calculation method where we have Ib
These formulas are brilliant. Thank you.
Glad they are useful and thanks for watching.
Brilliantly explained Sir! Thank you.
Most welcome and thank you for your support. Dave.
Omg what a fantastic video keep up the great work 👍
Thank you Mark and thanks for watching. Dave.
Which max volt drop figure should be used to determine the supply cable c.s.a. if the cable is to be installed from a house consumer unit to, for example, a garden shed that will contain lighting and power sockets?
I would call it a power (non-lighting) circuit up to the point it splits into lighting. Good question. Thanks for watching. Dave.
Always the best teaching, thank you.
Thanks for the feedback. Great comments, appreciated.
Dave be honest with you are brilliant Many thanks for your explanation.
Really nice comments and very much appreciated. Thank you.
Brilliant!!👏🏼👏🏼👏🏼
Thank you, appreciated,
Fantastic video again. Thank you so much for the great explanation
Glad it was useful. Dave.
Wow! This is video very informative and the best tutorial on the topic for me so far. I really appreciate it. Thanks for sharing it with us.
Glad you enjoyed it. many more in the pipeline.
@@learnelectrics4402 wow! Good to know. That Dave
Brilliant and simple explanation than IET teaching tecnic . Other wise No one understands go with books up and down. going mad.
Thank you very much sir.
Fantastic comments. Thank you Susantha, and thanks for watching. Dave.
Thank you. Lern lots.
Thanks Susantha, lots more to come. Dave.
Brilliant dave nice one 🙌🏻🙌🏻
Thank you Mr K. Appreciated.
You are simply the Best
Wow, thank you, appreciated. Spread the word. Dave.
Thank you very much sir. This is much easier than the school's teaching methods. You are genius. 🙏🙏🙏
Nice of you to say so Susantha. That's the idea of the videos. Unfortunately many schools and colleges have to teach you what is in the prospectus. I show you what you need to know. Thanks for supporting the channel and do tell your classmates about LearnElectrics, it all helps. Dave.
Thanks you so much for the video
My pleasure, thank you for watching, very much appreciated. Dave.
This has been a help! My teachers say they'll help me with VD but never get around to doing it
Now I just need to hunt for the pages I need
Have a look at this video of ours, it will really help. Dave.
Voltage drop formula for electricians.
czcams.com/video/ej3-6wcHfkE/video.html
Very informative video, subscribed definitely going to be looking through plenty of your videos.
Welcome aboard, and appreciated, There are many to go through and lots more to come. Thank you.
Thank you very much my friend
Thank you too, thanks for watching.
Beautiful Explanation
Thanks for liking, appreciated. Dave.
amazing thank you.
Great feedback, thanks.
Very good explanation, not seen the mV shortcut before, but then I am mostly on XLPE cable, so presume it is different for that.
Thank you. I try and show different ways of approaching the calculations, especially if you have no books with you - it happens. Dave.
Superb content on your channel- I wasn’t taught this at my college 👍
Thanks for watching Danny. I try and cover all points, Dave.
Brilliant video once again👍🏻
Thank you Mr D. Great support.
Great teach you are sir GOd bless you
So nice of you to say so. Thanks for watching. Dave.
Thank you so so so much Dave. You are brilliant by all ways. I wonder if I can use this formula for all cable sizes or is it limited to a certain CSA please?
Limited to 16mm. It sort of works for bigger sizes but then there are other things happening as cable size and current increase. Thanks for the question. Dave.
Thanks David For taking your time and making these videos could for everyone specially me can you also make a video on Three Phase Volt drop Thanks
Thanks Emi, that is on the list to be done. Thanks for watching. Dave.
Brilliant 👍💥💥
Thanks for the feedback, appreciated. Dave.
Hi Dave, it was wonderful. thank you so much for sharing your knowledge with us. I really appreciate it. As far as I remember, you had another video with the similar idea about finding maximum Zs without tables in reg book. could you please remind me what was the title of the video?
This link will take you to the video - 35 is the Magic Number
czcams.com/video/URBD4llLU6Y/video.html
Thanks for watching, Dave.
Many thanks
You are welcome, thanks for watching.
Thanks, if there are some rating factors in place, should we use the Ib with rating factors added (i.e. Iz) for voltage drop calculation?
No, use the actual current being used. Rating factors give you a pretend current to work out bigger cable sizes to compensate for insulation etc. The actual current will remain the same.
Great video, very useful, thank you. Just one question, how does this formula accommodate any rating factor which may have to be applied, or am I on the wrong track?
This video is just on volts drop, rating factors etc. will need to be taken into consideration in addition.
Have a look at this video on rating factors and condition codes. Thanks for watching.
czcams.com/video/YQpDDBoZp7c/video.html
Hi Dave this method doesn’t seem to work with lower values.
Its always worked for me David. In the video I do explain that the Regs books rounds numbers up or down and you will get some very slight differences in the book.
Well done
Your support is appreciated. Thank you.
I saw this comment and I too am confused
"
High Blean - B&B
2 weeks ago
I'm a bit late to your party but what a great party you are having! This set of videos are excellent and delivered in a clear, concise and understandable manner. You have even managed to take the terror out of the maths!
However, there is a but!
I have taken your example 3 [about 13 mins into the video] and I used some real-world figures that are applicable to me so that I can better understand. I have looked at the minimum cable size for fitting an 8.5Kw shower with an 8-meter cable run from the consumer unit in total.
So this was 44 X 8500 X 8
----------------------------- = 1.13
11.5 X 230 X 1000
This appears to suggest that the cable only needed to be 1.13 so the next standard cable above is one with a 1.5csa
What have I done wrong?
If you have the time and inclination I would be keen to know where I went wrong."
=========================================
I have altered it to remove the typo so what is going wrong with their and my calculations?
44 X 8500 X 8
---------------------------- = 1.13
11.5 X 230 X 1000
It would be good to see the issue explained.
That's right David. Because a short length of cable is used, the volts drop is going to reduce. This formula shows that reducing the length and keeping the volts drop constant, something else must change and in this case the csa. Don't forget that you still need to consider Ib In Iz which, at 8.5kW is going to force you to a 40A fuse and 10mm cable. Great question, thanks for watching, Dave.
@@learnelectrics4402 Thank you for your time, I am knew to all of this and just working through this for interest. I am not familiar with these terms " consider Ib In Iz " can you expand?
You are a legend 👍
Thank you, great feedback. Dave.
Hi would i be correct that if it was a ring circuit using 2.5mm sq 60 meters long you would devide the final answere by 4 giving a vd of 8.448.
Have a look at this video, it shows you the calculations and why.
RING CIRCUIT VOLTAGE DROP, click on the link below
czcams.com/video/blPi_pZ1jRQ/video.html
You can look up any video on the learnElectrics.com website. Put a keyword in the search box and it will list all the relevant Videos. Thanks for watching.
You did it 😉
Go ahead
Thanks for the support Michael, appreciated.
excellent math do more please thank you Dave
Oh yes, Azizur, some good maths coming up soon. Keep watching and thanks for the support. Dave.
Super video. Can I ask how you work out VD for 24v or 12v circuits please?
Yes you can Alan.
The next video on Monday 21st March is part 2 of these easy voltage drop videos and actually starts off with 24 volt voltage drop. Thanks for your support. Dave.
Hi Dave can we have a video showing how to calculate cable resistances over given lengths and csa’s please
Have a look at this video
CABLES LENGTH CALCULATIONS and R1+R2
czcams.com/video/Qq_9MNH8XxU/video.html
Hope it helps.
We are doing another video on lengths in a few weeks, keep watching.
Don't forget, there are loads of searchable videos on our website.
Dave
My power meter shows a non-load voltage at 247.5 to 249.5V at the further point away from the CU. Would the allowable voltage drop under max load be more than 11.5V, given the actual non-load voltage is already 17.5 to 19.5V above the assumed 230V standard voltage?
The actual measured voltage of most UK installations is 240 volts plus. 230 volts is the theoretical voltage. Calculate it using 11.5 volts and if your calcs are ok, you shouldn't have a problem.
Thank you for the great explanation. Can you please work out the units in the equation, I got confused how you ended up with unit of Volt. Thanks a lot.
The equation for volts drop is mV/A/m x Ib x L / 1000
That puts A and m on the bottom. They cancel out Ib and L leaving mV over 1000/
So Vd = volts.
Hope this helps. Dave.
Dave does this “no regs book” calculation work for all cable types? (Pvc/pvc, swa, singles in conduit micc etc)
Just the ones listed in the video, pvc/plastic single phase up to 16mm, which is 99% of domestics. Thanks for asking. Dave.
Urgent attention needed at 10:07. When you apply the voltage drop method for determining the cable size of the 6Kw heater you had 4mm² but when you use the cable calculation method where we have Ib
No attention required Daniel. 6kW is 26 amps and 4mm conductor easily takes this.
have a look at this video on watts, Hope it helps and thanks for watching.
czcams.com/video/4BixVh4mLKw/video.html
Hi Dave, might be a silly question......if I need to find out 3 phase, do you just substitute the voltage value again or is there another video on this please? This video already help immensely 😊
I have that on the list to be done. Thanks for the prompt to get it done. Dave.
I appreciate your efforts of this lacture but u say this formula using up to 16mm crosse section eara my qution what the formula using for alther size thanks
There are formula tables for larger sizes, three phase etc. that take into account other factors too,
how about the situation of a three phase 415 volts? is it gonna replace the 230Vac in the formula?
Thanks for the question. I will be doing a video on 3 phase voltage drop etc. in the new year. Dave.
@@learnelectrics4402 and please include voltage drop in aluminium coductors too if its ok with you.
i am using australia and New Zealand (AS/NZ) rule. does the formula also suits what we are doing?
Hi Dave, could you please make a video about AFDD device. Thanks
It's on the list Imran, thanks for your support. Dave.
Length of cable is length in one direction. For radial circuits it’s full length and for ring circuits is it half the length of circuit?
Aman,
Take a look at this video, CABLES LENGTH CALCULATIONS and R1+R2 on the link below
czcams.com/video/Qq_9MNH8XxU/video.html
Thanks for watching.
Dave.
Hi this formula for Single phase only or can use it for 3phase also thanks
These are for single phase up to 16mm. Different three phase cables use different volt drop figures.
Thanks for watching, Dave.
@@learnelectrics4402 thanks sir
Hi sir please tell me base uint of mV/A/m is 44.
Yes, that's correct. For 1mm copper it is 44. Dave.
I'm a bit late to your party but what a great party you are having! This set of videos are excellent and delivered in a clear, concise and understandable manner. You have even managed to take the terror out of the maths!
However, there is a but!
I have taken your example 3 [about 13 mins into the video] and I used some real-world figures that are applicable to me so that I can better understand. I have looked at the minimum cable size for fitting an 8.5Kw shower with an 8-meter cable run from the consumer unit in total.
So this was 44 X 8500 X 8
----------------------------- = 1.13
11.5 X 230 X 10000
This appears to suggest that the cable only needed to be 1.13 so the next standard cable above is one with a 1.5csa
What have I done wrong?
If you have the time and inclination I would be keen to know where I went wrong.
Your top row is correct, the bottom row should be 11.5 x 230 x 1000 not 10,000. Hope this helps. Dave.
@@learnelectrics4402Thank you for getting back to me this is really appreciated.
Yes, I have shown 10,000 instead of 1000 but this is a typo! From what I can see the suggested cable is still only the next size up from 1.13!
44 x 8500 x 8 = 2,992,000 / [11.5 X 230 X 1000 = 2,645,000] =1.13119-
44/CSA is applicable for 3 phase?
If your calculating between the three phases to neutral, yes. there will be a video on 3 phase Volts drop soon. Thanks for watching.
Can we use these formula for DC circuit??
Reg 110.1.2 says that AC and DC voltages are included.
I used an American on-line calculator some time ago - all in AWG sizes and both AC/DC voltages gave the same percentage volts drop.
We quote 230VAC in the UK which is an r.m.s value equivalent to DC levels so the calcs are using figures based on 230V AC r.m.s and not 330 V AC peak. Hope this helps.
The same for minimum CSA in mm2
Thanks for watching. Dave.
44 it is constant value??
44 is the standard value for 1mm copper conductor. We can work everything else out from that as the resistance is a linear value. thanks for watching. Dave.
Design current Ib can’t be the same as the protective device current. There has to be selectivity between the 2. I always thought that In would be greater than Ib
The Regs say In is equal to or greater than Ib.
Thanks for watching.
👍👍
Thanks Mike.
Can this be used in exam conditions..?
You can use any method that works for you and gives the correct answer from the 4 choices. After all, we sometimes use just memory, some things we just remember. What you cannot do is write anything down in the Regs book for the exam. Some exam centres actually give you their copies of the Regs for the exam, so there is no chance of writing stuff down. Its an exam fail, best just to learn how to find the answers. Good luck, Dave.
Does CSA mean cross sectional area?
Yes it does. Usually in square millimetres in the UK. Thanks for watching. Dave.
@@learnelectrics4402 Thanks for answering and well done. You're a very good teacher.
What if it is 400 or 415v?
I've been asked to do a video on 3 phase voltage drop etc. Its on the list. Thanks for watching.
How many milliamps is for Aluminium ?
Thanks for asking.
You will find the data for Aluminium cables on pages 476 onwards in the Brown Regs book.
Hope this helps, Dave.
11:15 had 5.04v when i used the main formula, but had 5.10v when i used the formula with CSA
Yes, that's right. The accurate readings use 44 as a base. The regs book and osg round up the figures so will be every so slightly different. We're not going to worry about six one hundredths of a volt difference. Thanks for watching.
@@learnelectrics4402
Urgent attention needed at 10:07. When you apply the voltage drop method for determining the cable size of the 6Kw heater you had 4mm² but when you use the cable calculation method where we have Ib
@@learnelectrics4402 Thanks for your explanation. I really followed the teachings
🎉❤
Thank you. Appreciated.
I don't understand how the base number is 44? thanks
There is a scientific reason behind it. worked out by the boffins. It works. Thanks for watching. Dave.
The material of the used conductor must be taken into account - which is not included in the formula
Absolutely it must and in these videos we are using copper. If you need data for aluminium cables there is a table for this in the regs book.
I find this useful but I know how to do this the long way very well. I don't think people who don't know how to do design should be using this, they will definitely make mistakes.
Thanks for watching Steven.
@@learnelectrics4402 I really appreciate these videos, you have done a lot of good work.
If a power circuit has a volt drop of 6%, what are the practical consequences of this non-compliance?
I think because the load draws the same power (P=current x voltage), if the voltage is lower, the current becomes greater and may cause cable stress heating.
There will be less power in the appliances. Your kettle may take longer to boil etc. Example - a 3kW kettle at 200 volts will only work as efficiently as a 2.5kW kettle. Good idea for a video. Thanks for the question. Dave.
Thanks Mike, see answer above. I will do a video on this soon. Dave.
Ok
Thank you.
ànother greeat video
Thank you, much appreciated feedback. Dave.
Don't get where 44 came from?
Its all based on 1mm copper cable losing 44mV per amp per metre. 2mm is twice as big so half the loss - 22, and so on. Its a scientific number worked out by the boffins that we just accept and use. Hope this helps.
Dave, you never cease to amaze me! Just when we thought it couldn't get any better, you surprise us with another little gem. 😁👌
Very useful bit of information.
Thanks again Dave, having trouble keeping up with all the videos but trying my best to fit it in somehow. 👋