BREAKER AND CABLE SIZES FOR ELECTRICAL CIRCUITS.
How to select the correct size breakers and cables for your electrical circuits. This video will introduce you to the steps needed to calculate maximum loads on a circuit; how to use charts to determine the correct circuit breaker for the load, and how to select the right size of cable for the job. Avoid the dangers of installing cables that are too small and give rise to fire risk, avoid over sizing cables and wasting money on excess copper; the right size matters. Use the tables to ensure that the circuit demands are properly balanced and will function safely and correctly. With just one easy to use formula, this video will enable you to plan jobs more efficiently with the confidence that it has been done correctly according to the Wiring Regulations. Once learnt, remembered for life.
To view all our videos, click on the following link
/ @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. kzhead.info/tools/YaJQnpO4XAp0yCgqzMkmfA.html
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When you fully understand something it is easy to explain said Isacc Newton. Your explanation was simple and complete. Thanks
Thank you Chris. We really appreciate this feedback. Dave
9 times out of 10, yt influencers give out incorrect information. This guy does NOT.. Excellent stuff sir . Sub from me
Thanks for the sub, really appreciated. Dave.
Finally someone has explained the actual calculation of what we were trying to learn 👏
Thanks for the great comment. Lots more videos to come, including more calculations. Dave.
@@learnelectrics4402 hi dave 👋today is Christmas day "so I'll bid you merry Christmas 🎅 "and a big thanks for your teaching videos " I've been in the building trade for nearly 40 years now? As a bricklayer ☠👻spent most of my time on sites 'but went self employed in 2000 ' I've learnt a little bit about electrics 'wired up a few sockets now and again? And normally had to get electrician to check it over ' 🤪but recently I came across your videos " and got interested in expanding my knowledge of electrics 'I've watched other videos of similar advice "but found yours the one that struck me the most ' its not elaborate or highly glifick "but some how it works for me?? Think it comes down to how someone can get a difficult scenario across ! I find your instruction easy to understand 😃I'm going to follow you deeper into this "and get more equated with this "wish you could of taught me years ago "🙈all the best my friend "have a good New-year 👍
I can't begin to tell you how grateful I am for these videos although I retrained 7 years ago as a older student know 53 they give me a much better understanding I am now confident enough to help some of the younger apprentices with issues or just show them your videos keep them coming matey 👍
Thanks Mark, brilliant feedback, makes our day. 53? Still got loads of life in you yet and yes, it is good to pass on knowledge to the younger electricians. Thanks again. Dave
Mark, Your just a young man, Im 66 and still going strong so dont worry about age mate.
@@angelofranklin1 66 that's excellent I just noticed I put 53 don't know why because I'm 55 🤣 tell me I'm going be OK 🤣
What a video, great at explaining and making things more clear and easier to understand! Bravo!
Thank you so much David. We really appreciate your positive comments. Dave.
Thankyou described it in a easy to understand, in the past I have looked at books on electrics,and they made it sound so complicated, but with your explanation I got it straight away,once again thanks
Glad you liked it. Keep watching James. Thanks Dave.
You have saved the day once again mate. I was sweating over this theory on a training course and its a relief to now understand it. Thanks to your excellent communication skills. 👏
Glad we could help John, spread the word. Dave.
Yes, I completly agree. Easy to follow through.
I've been looking for this for a long time now. Well explained, thanks a lot.
Great Pabor, glad it was helpful. Lots more to come, check out our other 50 plus videos.
Fantastic explanation really informative. Completed a domestic installers course with a well known training centre and this is great to keep my knowledge from rusting up. Great stuff and easier to understand.
Thanks Robert, really appreciate the good comments. Dave.
Master your videos are superb. I'm not yet an electrical engineering student but I'm about to be, watching your videos is pretty good for a lost sheep. After tons of research this piece just made my day.
Thanks Matthew, good luck with your studies. Thanks for watching and keep learning. Dave.
Love the video, the way it is explained is brilliant, grateful of the videos👍
Thanks for the really positive feedback. We try our best. Lots more to follow. Dave.
Thank you so much, your explanation is perfect. In class they gave us handouts stating the steps of finding the cable size with these Ib, In, Iz symbols, never understood the meaning of these symbols, and now that i viewed this well explained video everything became clear
So glad that it helped. Tell the rest of your class mates about us, it makes it all worthwhile to keep making more videos. Dave.
Thank you so much for the lesson. It was so easy for me to understand the way you explained.
Brilliant. That's exactly the feedback that we want. One video, one topic, made easy. Lots more videos on the way. Dave.
i learnt more from you than from my 2 years at the college... keep the excellent work up
Thanks, will do Imran. That's fantastic feedback. Dave.
Hi Dave, I recently completed and passed an excellent domestic electrician course at EC4U in Ditchling. Your video series is a superb “old-school” reinforcement of these key principles and in some cases has offered an even clearer explanation, or at least a different perspective on the same learning points. Being an older learner who has recently changed to the electrician career, this series has been brilliant. Thank you!
Thank you Mike for the very positive feedback. Our aim is to produce videos that tackle just one subject each week and they are based on all the questions and difficulties that electricians and learners have had over the years during the time that we ourselves have been working on the tools and as assessors and instructors. There are many more to come yet, keep watching and thanks again. Dave.
Mike. How about the Domestic Electrician course in EC4U? I also want to join it.
@@hingninwong yes, look them up on google. The website is easy to navigate. Good luck!
@@MikeSmith-tx2lp does the domestic electrician couse fit your purpose, such as capable for you to do the minor electrical work ? Any comment to this course?
Excellent video. I learned a lot about choosing the correct wire size and fuse to be used.
Thanks. If the video helped then its done its job. Dave.
Again very well explained. totally at ease with the way you explain things. very well done
Thanks Iqbal, great comments.
Its great the way you simplify it by using that box method,really helpful.
Thanks Marc, appreciated comments. Dave.
It's very important idea and concept about Electrical Engineering
Thanks for watching. Appreciated. Dave.
Thanks Dave, your a Legend loving all of your video Have a great Christmas & take care
Thanks Johnny, thanks for the support and have a great Xmas yourself. Dave.
Thanks a lot dude. Just about to complete my engineering apprenticeship and now wish to base my career from an electrical bias. These theories aren't so intimidating when broken down and structured as well as you have demonstrated here 👍👍 will be sure to watch more. Thanks again
Thanks for the feedback. There is access to over 200 videos on the website LearnElectrics.com Dave.
Hi Dave, very well explained thank you.
Thanks Angelo. Thanks for watching.
A fantastic help. Thanks for the video!
You're welcome. Thanks for the support.
If i am not wrong, there is not even a channel like yours... It is helping me... Thank you for everything and may ALLAH(GOD) bless you... From Mozambique
Thanks Mohammed. Thanks for watching and I'm so glad the channel is helping. I have some very fond memories of my time in Africa. Beautiful country, amazing skies. Dave.
Great video, very well explained, clear and to the point. Thank you very much
Glad you enjoyed it, thanks for the support.
Thank you for this video, something what i thought id never get my head around made it very easy by watching this. once again thank you
Great to hear that Jess. If the video helped, its done its job. Dave.
Thank you so much for these valuable videos. Much appreciated 🙏
Glad you like them Aleko. Thanks for watching.
Love it! Thank you once more
Thanks for watching.
Again an excellent video and thank for the great explanations.
Thank you. Glad that you are finding them useful. Dave.
Thanks once again for well presented technical material in the subject of electrical calculations Kindly keep them coming Thanks
Thank you, I will, lots more to come. Thanks for watching. Dave.
Thank you for the breakdown it always helps when it’s explained correctly. Please keep up the good work you have my full support. Regards Karamat Hussain
Thank you so much Karamat. Great comments. Dave.
Dear your explanation was so simple and it is delivering your experience. thanks ......
Thank you. Great feedback, appreciated. Dave.
Great information
Thanks for watching, appreciated.
Very easy to understand. Great video. Cheers
Glad it helped, thanks for watching.
Thank you for your excellent video.
Great comments. Appreciated.
you're the great explainer.
The great explainer, sounds like a song. Thanks for the great feedback, really appreciated. Thanks for watching. Dave.
Well done again...
Thank you, thanks for watching. Dave.
Thankyou for your amazing video.
Glad you enjoyed it, thanks for watching.
❤fabulous video ❤
Glad you enjoyed it, appreciated.
Just wow this video is gold
We're glad you like it. keep watching, more to follow. Dave
Thanks for sharing it with us
My pleasure Daniel. Thanks for watching.
Very clear and easy to understand 👌
Great. That's exactly what we wanted to achieve. Thanks for watching. Dave.
Thankyou really clear and easy to understand
Glad it was helpful Paul. Thanks for watching.
You made it simple for us...
Great feedback, appreciated. Dave.
another great video, i did miss the normal couple practise questions you put in though.
This is an older video, before I started doing that. Thanks for watching. Dave.
Perfect thank you
You're welcome Coby.
Thankyou really good and clear to understand.
Glad it was helpful paul and thanks for supporting the channel.
Really really good video, thanks,
Glad you liked it. Thanks for watching. Dave.
Very good explanation
Nice comments, thank you. Dave.
Great ,subscribed.
Thank you Stephen, much appreciated. Dave.
Brilliant A1
Thank you. Great comment, it makes our hard work worthwhile.
Thank you for explaining this better than the big book! It's quite a simple theory, made incredibly confusing and baffling by the wording in BS7671. I don't know why they don't just print the formula in BS7671 instead of the 3 bullet points.
Unfortunately we have no control over how the boffins lay out the book. Glad it helped. Dave.
Wow! This is very informative, thanks for sharing it with us. It worth it and the best tutorial on the topic for me...dl
Glad it was useful.
I'm glad to get ur channel sir,10Q
Glad that you lie the channel Aeneas. Lots more good videos to come. Dave.
NOT , I'M NOT LIE U. I swear.
Love yr video's can you please make a video on two way lighting circuit and fault finding if the wire's mixed up on celling rose and the switch thankyou
We have lots of videos on all aspects of lighting on our website. Go to LearnElectrics.com and put lighting into the search box and you will get a list of all the videos about lighting and direct links to the videos. Hope this helps, thanks for watching. Have a look at lighting Differences on this link kzhead.info/sun/gamjc7yHlox5aJs/bejne.html
I've done 3 years of evening college, honestly wish I'd come across your videos first.
Well, you've found them now. Stick with it, it really is a good trade to be in. It's taken me around the world several times, worked in some fantastic places. Dave.
Brilliant thanks
So glad you enjoyed it. Thanks for the positive comments, they do help. Dave.
Thanks really perfect
Thank you, great feedback, appreciated.
First of all I want to say thanks a lot for all Your excellent video. I would like to ask about 3 phase circuit how we can find out about Ib and cable size .
Thanks for watching, glad you found it useful. We will be posting a video soon on 3 phase cable sizes, lots of people asking for information. Good request. Dave.
Fantastic video. What would change in the calculations if it was on a tt system. ?
Nothing should change. Install conductors with sizes as if they were in a TN-C-S system. They still have to take overload currents. Its just that your measured ZS will be all over the place. Dave.
Hi Dave, another excellent video, we all thank you for all you are doing. I'm confused about the choice of cable size. On the chart on page 72 I see many entries with a rating of 32A that fit with the 100 installation method, why did you say there is only one? Also, do you know where in the book we could find the installation methods? Again, thanks for what you are doing.
You will find installation methods begin on page 433 of the Wiring Regs book. If it is flat profile twin and earth we choose the nearest size cable equal to or greater than 32A which is 6mm. See Table 4D5 on page 456. Hope this helps. Dave.
Thanks for help
Always happy to help Reza, it makes the world go round. Dave.
Brilliant
Thanks for the feedback. How is good old Shropshire, I lived in Shrewsbury for 20 years before heading south for the sun. Thanks for watching. Dave.
Thanks useful video. For the video of playing at 8:57, may I ask why not choose cable size of 10mm/4mm?
See above.
Fantastic video again thank you, if you were installing a domestic cooker circuit for a 16.5kw cooker and induction hob (very large i know) how would you go about that? Would you install a 16mm cable that would be able to handle the full maximum load of 67amps or with diversity included would say a 10mm cable would be sufficient? Installation method ref method c no insulation and 8 meters of cable for the circuit Sometimes these scenarios confuse me a little and i don’t feel 100% confident with selecting the correct size cable. Any help would be greatly appreciated thank you
Thank you for watching and the great comment. We have a video that will show you how to calculate diversity for your cooker. The example in the video is for a 7kW cooker, just change the necessary numbers. Cheers, Dave. To view the video, DIVERSITY and MAXIMUM DEMAND, click on the link below kzhead.info/sun/h7preb6spKuaoGw/bejne.html
@@learnelectrics4402 thank you very much your videos are extremely well presented and helpful keep up the great work
Thanks again. Happy to help. Dave.
Hi Dave, When you mention @3.23 "larger cable " "paying for extra copper that you do not need". Is this the only reason? Will a larger cable not affect anything else, only cost?
A larger cable will carry more current more easily and will not heat up at the same rate as smaller cable sizes, We can always install bigger cable and know that we will not have a problem, except perhaps with getting the cable into the terminal holes, 10mm shower cable will work for a lighting circuit but no way will it fit in the switch (an extreme example, sorry). So yes, that little section comes down to cost. Good question and thanks for watching. Dave.
Im training as an electrician and your videos are very helpful, i can see this calculation wiuld be good for an individual radial or ring say for a shower or cooker, how would this woek with lighting circit or socket? I am starting my NVQ level 2 in september so sorry if this is a basic question.
There are standard sizes that we usually use for each type of circuit. The important thing is that the cable capacity MUST be equal to or greater than the fuse/breaker rating. I'll be doing a video on this soon. Stick with it, its a good trade to be in.
Really useful videos for someone learning the trade. With regards to choosing the cable size, I'm just a bit confused, could you also choose the 10/4 mm too seeing as it also allows 100 as the installation method?
You can always go up in cable size, the difficulty might be in getting the conductors to fit in the accessory. Thanks for watching. Dave.
@@learnelectrics4402 Ah, I get it....thanks for answering
LOVE these
Glad you like them. Thanks for watching.
Thank you once again for a very clear explanation. Just one question: 8:28 you select the second row - even though I can see 6 rows with "100" as Allowed installation method (5 with 32 A breakers) Is this because the top 2 rows are for breaker type BS EN 60898? Could I also pick the 3rd row? (i.e. a 10mm^2 cable)? Thank you for your patience (I hope this question helps other students).
Happy to help. Thanks for the feedback.
Hi Dave, could you do a similar video for three phase?
It is planned Ed. Thanks for watching.
Seems easy enough as you explained in great detail, I am looking to install panel heaters in my flat, can these just be added to ring main or need a separate circuit, if a separate circuit then can I do myself to save money?
Consult the heater manufacturer's instructions. Some say that they can be plugged in, coming with a fitted plug is usually a good clue. Other heaters are recommended on their own circuit. Adding a new circuit assumes that you are competent and can notify the work to LABC afterwards. Only you will know if you can do this. If you are unsure, I would suggest using a REGISTERED electrician, but ask to look at his registration card (NAPIT, NICEIC etc) before giving him/her the job and before handing over any money. Tell them you want a Building Control certificate when the job is finished. And get three written quotes before making a decision.
@@learnelectrics4402 thanks, the heater doesn't come with a plug, needs wired in to a fused switch
I think it’s worth mentioning that when you’re calculating your design current, if it is a 3 phase system you would put root 3 at the bottom of the fraction and if you have a power factor you would put Cos(power factor) at the bottom of the fraction aswell
Excellent information, thanks for contributing. Dave.
Thank you for the video. What is the difference between "rating" and load" in the table on page 64. Is this assuming diversity of 80% e.g. the shower is off for at least 12 minutes in every hour of use?
Load is the amount of current you put through a fuse. A kettle might put a load of 13A on the circuit. A table lamp might have a load of half an amp The rating of the breaker in the consumer unit might be 20A or 32A if a ring Hope this helps. Dave.
thank you so much for clear clips. can I ask you if we have 63 meter cable length and use voltage drop formula vd={(44/6)*63*32 }/1000 the result will come to 14.7 volts and because its greater than 5% allowance means 11.5 volts is it acceptable ?
A 14.7 volt drop isn't acceptable as its above the values in the Regs. You would need a bigger cable size. Dave.
Thanks nice
Most welcome, thanks for watching
Is this an alternative method to using the 18th Edition BBB and using the design current x length of cable x mv/A/m x any grouping factors?
This video is about Ib In Iz. Condition factors are covered in a different video. Thanks for watching. Dave.
Thanks for your prompt reply. In your video, you said you choose 6mm cable is based on method 100 in 2nd row, but 3rd row also has method 100. So may I ask to explain more by based which Wiring Reg. , we should choose 6mm but not 10 mm cable? I have confusion to choose one between them. Thanks.
You need to look at all the information on each line. With 6mm cable the maximum cable length is 63 metres which is more than long enough for most domestic dwellings and this matches up with the rest of the information on the slide. If you install 10mm you can take the length to 105 metres. Hope this helps.
@@learnelectrics4402 Yes, i got it that based on the length of cable for the house dwelling in this case. Thanks.
A 6mm cable (6 sq mm) is fine when the insulation stays the same and the shower remains at 7000 W. A 6mm cable is near the limit. The user may well fit a 8000 W shower when a 7000 W shower becomes unavailable on replacement by a plumber. Or the insulation is upgraded. On balance I would install a 10 mm (10 SQ mm) cable.
Thank you
Thanks for watching, appreciated. Dave.
Thanks for good explanation But I need that book
Thanks for the good feedback Justin. The book is the IET On-Site Guide 18th Edition. You will get it from Amazon or google search it or even Ebay. MAKE SURE that it is the BLUE 18th EDITION copy. Any other colour will have different data on some pages and different page numbers and is no good to you. Good luck, and thanks for watching. Lots more videos to come. Dave.
This says In must be equal to or less than Iz - so in theory a length of 1.5mm flex is fine on a 16a MCB, given that they’re both rated for 16 amps?
Thanks for watching, appreciated. Have a look at this video. Dave. kzhead.info/sun/idiNhc-Np4NjhZs/bejne.html
@@learnelectrics4402Thanks for the reply, can I clarify something in the video you linked? It states the equation Ib ≤ In ≤ Iz, however the summary text states that Iz must in fact be greater than In. Just wondering, as the formula implies that selecting a breaker rated the same as the CCC of the cable is fine. So would a 10amp breaker be fine for a cable that can only carry 10 amps, for example?
Can you explain the digital scale on a multimeter for measuring resistance? The only thing I can find is a old vid from perkies talking about ohms scale?! Many thanks do you have an e mail I like to talk about the course I’m doing !
Thanks, I've put this on the to do list of videos. Dave.
Could you plz do a video on SELV AND PELV circuits?
You must be a mind reader. That video is planned for February. Keep watching, thanks. Bux
@@learnelectrics4402 lol
Hi - when you say IN must be the same or just above IB, how do we quantify or calculate 'just above' ?
If Ib is 9.9A then you want a 10A breaker. If you put a 40A breaker in circuit that is too big.
Thanks
Thank you Maryam, appreciated. Dave.
Thankyou
Very welcome. Thanks for watching. Dave.
Can I purchase a copy of the on site book in paper version as I find it hard reading from screens
Yes Richard. Amazon is probably about your cheapest. The current 18th Edition is a blue book, BUT Amendment 2 is due to be issued very soon. Whether that is weeks or months we don't know. If you buy the blue OSG you may need to buy the new amendment 2 when that comes out. Current price for the On-site Guide is about £30 depending on what deals are on.
I’m confused, on page 72 for cable sizes you say there’s only one that matches the reference method 100, but there’s actually two? 32 amp 6mm and below it 32amp 10mm? Also is there another chart that goes higher than 40A on page 64 ?
The two 100 references are for different cable lengths - 63 metres and 105 metres. A longer run will need 10mm cable. Fuses/breakers above 40 amps look at pages 61/62/63 in the Wiring Regs. That's a good point, perhaps I should do a definitive list for all fuses/breakers and put it on the website. food for thought. Thanks. Dave.
What if 3 shower is installed for single 32amp circuit breaker? Will it be ok?or do we need to recalculate
Definitely not ok. Every shower should be on its own circuit. Putting three showers on one breaker will contravene the Wiring Regulations, contravene the Building Regulations, contravene the Electricity at Work Regulations and contravene the Health and Safety at Work Act. That's just for starters, you will also invalidate any trade insurance you have and any professional indemnity insurance and invalidate the buildings insurance.
but will this table be inside the regs A32:2022 book ?
Not that exact table, that is my own table to show you ta simple relationship. Thanks for watching. Dave.
Can this formula work for three phase 440 V?
This video is just about single phase 230 volt circuits Zeeshan. We are making a video for 3 phase cable sizes very soon. Thanks for watching and thanks for asking. Dave.
can we use 415v instead of 230v to calculate design current???
In some instances you will need to use 400 volts, I'm thinking of 3 phase plus earth systems where there is no neutral.
I have some questions, if I calculated the design current to be 102 A and I need to choose a circuit breaker, as you said that the circuit breaker needs to be bigger than the design current, can I choose 125A, 150 A, 200A circuit breaker? what is the difference? Is it appropriate to choose the 200A like the bigger the better? Just cut out the cost issues and focus on the safety of the system.
Thank you in advance for valuable lessons!
No, bigger is not safer. Ideally you need the same size or the next size up that doesn't exceed the design current. We want to fuse as close as we can to the design current for safety.
You are very welcome.
Morning is possible to get on side guide?
Thank you for watching.
Would a 40 amp circuit breaker be too much over the requirement for this shower installation ?
Generally 9kW shower is 40A, 7kW shower is 32A.
Thank you for fast response, very clear videos
You are very welcome Gerry. Lots more to come.
👍👍
Thanks Mike, thanks for the support. Dave.
For Showers/Heaters shouldnt the RCD be 10mA in BS7671 18th instead of 30mA?
30mA is the recommended RCD. You can fit 10mA if you wish but you may find you get nuisance tripping,
Anyone know the correct onsite guide table numbers for the new brown book ?
Use pages 3,4,5 of the OSG to find what you are looking for as the tables are spread throughout the book. thanks for watching. Dave.
Ref method 100 @ 8:00. The maximum load is 26A but our design current is 32A. Wouldn’t you use the one below?
Have another look at the video. Max load is almost 31 amps. Thanks for watching, Dave.
@@learnelectrics4402apologies, not 32A I mean 30.43A. I was referring to the second you highlighted in the table. There’s a column that says “Load (A)” i wondered if that was the maximum load permitted, and if so, that is lower than the design current.