A look at the adiabatic equation

[@cestemshow]

Just to re-iterate! The second equation describes the time you live/neutral cables will last during your Zn fault current. Don't think I made that clear enough. It is NOT the disconnection time! You want your cables to last longer than the disconnection time of the given fault current.

[@trollobite1629]

Right, you've forgotten your onsite guide so you decide to show off by remembering stuff and working it out, you're moaning that 23 minutes isn't enough time but somehow you managed to find the time to drink a cup of tea and spill it all over your paper work :-) Seems to me that you've been hanging out with the apprentices for too long :-) Dude these are excellent videos and I really appreciate you taking the time and making the effort to produce such high quality work. 10/10

[@cinglis8310]

Absolutely fantastic video! You have managed to join so many dots for me with your narrative that I am now fine with all of the content covered here. Looking forward to seeing your other videos and especially the design series.

[@cestemshow]

Happy it helped! Thanks for watching.....The rest of the design series will be coming soon, keep tinkering with it because i want it really good.....

[@alanbeard4871]

Great video. Hope you may be able to answer a question that has been bugging me for a while. Why do we always use Zs and the end of a circuit for these calculations and ignore for example a radial circuit where for example the first socket is only 50cm from the consumer unit, which would have a very high fault current.

[@cestemshow]

Good question! It is because we then know the lowest fault current on the circuit and therefore if that still is enough to disconnect the device then it must be enough at any part of the circuit. We check out incomer Pfc to ensure its not too much fault current at the incoming location which would exceed the breaking capacity of the device. .

[@bartd75]

these videos are brilliant for any apprentice or for any older sparks that needs the cobwebs blown away. brilliant stuff

[@cestemshow]

Anything to help the next generation to look after our pensions 🤣😂

[@angelofranklin1]

Very good lesson given, well explained and very informative thank you looking forward to your lessons.

[@cestemshow]

Many thanks!

[@goaway9487]

When determining the time side of the equation you should also consider that in a 3phase circuit a live to live fault can occur & therefore the voltage for your fault current calculation must be 400v for a line to line voltage between phases.

[@Daztronic84]

Youre doing a brilliant thing here. Thanks! I look forward to the design stuff.

[@cestemshow]

Much appreciated!

[@pesti_ja1]

Excellent video, thanks for posting. Looking forward to your design series.

[@cestemshow]

They are going to take longer than my usual because the editing is increasing to make them easier to watch so i may post a few classroom ones in between 👍

[@dsbelectricaldavidbetterid8448]

if you are hitting quicker than 0.1 sec say 0.01 due to amount of current i2 produced would you need to consult manufactures data for the i2t and use this

[@cestemshow]

Yep....sure would

[@dsbelectricaldavidbetterid8448]

great information thanks for doing them gives me a quick refresh of everything

[@cestemshow]

Glad you like them!

[@kylepeace3252]

Very good video, this has really helped me to understand the process and values required for the equation and put in a very clear way........thanks for your time.

[@cestemshow]

Glad it helped, always lovely to hear good feedback. Thank you!

[@mykl7964]

Thanks, great break down of the adiabatic equation, was not taught the way you set it up first. Makes it much easier to transpose, and great reference to books thanks.

[@cestemshow]

Thank you so much, very kind words! Glad it helped 😊

[@faisalmohammad91]

do you have any videos on how to calculate supplementary and extraneous bonding?

[@cestemshow]

Do you mean calculate the need to? or how to calculate the resistance of the cable?

[@faisalmohammad91]

@@cestemshow no..how to size the supplementary bonding and how to size extraneous bonding ?

[@cestemshow]

Main protective bonding is sized using the supply conductors (table 54.8 for PME) or read reg 544.1.1 supplementary bonding has to satisfy the following equation found at reg 415.2.2 so it depends on the local electrical points and there Ia (disconnection current) if you use an rcd then the range is obviously extended as the trip current is much much less than a 6A type B mcb for example...... so if you had some pipes near a metallic faceplate on a shaver point then the max resistance between those two "touchable" points would be 50v/(6x5)A= 1.6 ohms it is 6x5 because a 6A B type mcb would most likely be serving the shaver socket and B type means we multiply rating by 5 (worst case)......where as if there was an rcd protecting the shaver point (which nowadays it would be) would be 50v/0.03A = 1667 ohms hence why the need for supplementary bonding is usually eliminated by using an RCD

[@chrisnunn81]

Thanks for such a informative video and making transposition seem a lot simpler than before

[@cestemshow]

It should be made simple because it really is when you get past the fear of getting it wrong!

[@brianhartfield1170]

Quick question if calculating for main earth. For the protective device. Do you use the suppliers fuse or the boards main switch? Are you even allowed to use a smaller cable for main earth if calculated correctly or does it just have to be 16mm

[@cestemshow]

We use table 54.7 for sizing earthing conductors but if you wanted to confirm you would use the prospective fault current for the building. But just be aware that the earthing conductor may need to do more work than that hence why it's best to use table 54.7 in bs7671 or table 54.8 for main protective bonding conductors....

[@Graham94]

Amazing video! One question, If we did all this to find out the minimum CPC to use, how did you know to use 1.5mm cpc initially for the formula.. on Table I1, to get 19.51 for R1+R2?

[@cestemshow]

I will need to watch the vid again to remind me but it might just be an example I knew would work. There are ways of getting there faster by transposing the equations but I don't remember doing that tbh. Il check it out and get back to you, OK?.

[@cestemshow]

So yeah I remember now. When using this method of design you are calculating your lives and then choosing a cpc. If you chose the same size as the live then it will prob comply but be quite wasteful. What I've found is that starting approx half the size of the live conductors seems to comply the majority of the time (there are exceptions) also if we take twin and earth cable this seems to support that assumption as the cpc is usually smaller than the lives so I went with the knowledge that 2.5/1.5 6242y cable exists and started there I believe and it complied. You could guess any cable and check it for compliance. The more you play with this the more you will see the patterns so go nuts trying different cable sizes and see how it affects the faults current and therefore the adiabatic result etc.

[@lorus511]

@@cestemshow The new cable coming in next year will have cpc same size as line & neutral so will presumably do away with having to work it out.

[@angelofranklin1]

Can you advise as i am taking level 4 very soon would you use Cmin or Cmax in the equation. Appreciate in this case the current let through is 100 amps min required (5x20) for 0.4s, with a higher fault current reducing down to possibly 0.1 seconds. So we have two possibilities with the voltage between Cmin and Cmax with anything between 218.5 volts and and 253 volts.the latter giving a higher fault current. Or would you advise trying both.I think personally i would go for the worst case and use Cmax at 0.4 seconds. Please advise thanks.

[@cestemshow]

Yeah play with it and see the results. after a certain point we use the let through energy from manufacturer. The time current graphs of an mcb get rather whacky when you really study them. for purposes of 2396 id stick to simply 230v middle of the road. Ask your tutor specifically about this. We teach 230v at city and guilds. Higher fault current disconnects quicker so sometimes it can be misleading to think more current means bigger cpc because it takes longer for the fault to clear so more energy in that cpc for longer. I did do a design video where I try all 3 somewhere.........cant remember which one though :-) I think its the 30kw plastic forming machine video. .....or the 3 phase motor one.

[@cestemshow]

cmax helps us design switchgear and cmin for Zs .........thats what I was taught but then realised it doesn't always fit all boxes.

[@gbelectricks]

Craig, @ 17 minutes in, you calculate the ipf from the maximum zs at the remote point of the circuit (then use this in the adiabatic to calculate minimum cpc size) Would it not be better to calculate ipf somewhere nearer to the source (not at the remote point) as this would have given a higher ipf figure (which would have ultimately required a bigger cpc size from the adiabatic equation)?

[@cestemshow]

If the cables touched at the source then you would be looking at a different earthing conductor to see if it can cope. The adiabatic isn't very accurate to be honest. As the cable length increases you would get different fault currents along it. Closer to the source we have high fault currents which would clear quickly, at the end of the circuit we would have lower faults currents with longer time to trip. At the end of the day it's the difference between 0.01 and 0.1 seconds really. The cpc insulation would rise in temp but only for half a sec max so generally not an issue but the fact that your asking that tells me you " get it ". Keep playing, the more your circuit complies with Zs (well under max Zs) the bigger the adiabatic problem usually. But there are anomoly circuits you will find.

[@gbelectricks]

@@cestemshow thanks for the detailed response Craig, a lot of the knowledge I was taught (about 20+ years ago!!) was either not fully understood at the time or has simply been forgotten. Your channel is essential resource for younger trainees, sparks young and old. Keep up the good work it’s all really appreciated 🙏👍

[@Mohammeddhubaibi]

Hi, Why didn't you divide by the 1000. Zs= 0.35 + (19.5m.ohm/m × 50m × 1.2)/1000 = 0.35117 Ohm. The If = 230V / 0.35117 = 654.953 A. But we would calculate the Total earth fault Loop impedance is the sum of : 1. The impedance offered by the line conductor R1 2. The impedance offered by the CPC conductor R2 R2= 1.67 X R1 R1 = (0.2221 x 50)/ 2.5 = 0.4442 Ohm R2 = 1.67 X 0.4442 = 0.742 Ohm. Zs= 0.35 + 0.4442 + 0.742 = 1.54 Ohm. Then the If = 230V / 1.54 = 149.4 A. I don't know which is correct?

[@scottfisher7619]

really informative and delivered clearly, looking forward to the design series

[@cestemshow]

Thank you Scott. It's taking some time but the plans are set...... The shooting is time consuming but ultimately, hopefully, worth it...

[@garycooper1376]

Where in the regs do you work out the R1R2 of swa while using the armouring as the earth

[@cestemshow]

Its not in the regs sadly. Can be found in IET design guide or ask a manufacturer for a data sheet. can also be calculated but long and boring :-)

[@garycooper1376]

@@cestemshow i am abit of a geek though 👀

[@kienthucdienmattroi-VN]

what is the document you are using? Could you share me ?

[@cestemshow]

BS7671 is the title of it.

[@jollyfinequality9865]

Good evening Craig, this is the first video of yours I have watched. Having read the comments, most others have said all the good things I would say, so in short really enjoyed it. Liked and subscribed 👍 I shall enjoy watching some others now. I am from the older generation, sat my C&G 2361 & 2362 in 1988 & 1989, so helpful refreshers for me. How is the design series coming along? Keep up the great work.

[@cestemshow]

Thanks buddy, kind words. Thank you😊 Ah so you come from the best generation. I think I was the last of the indentured apprentices and count myself very lucky to have had the training I got at SEEBOARD. Unfortunately since then, many have had a bum deal with their training and there is so much more content to cover now in the same 3 years, I thought doing these videos for my students and anyone else would gain time for me to teach my students a more in depth view of the industry. Some do, some are still a bit lost but it certainly helps if one of the, is off sick :-) Design series is floating around. Im doing calculations at the moment but will drop back to my dream of doing a more documentary style design video.......They just take so long to edit! Thanks again.

[@jollyfinequality9865]

I did not perform well at school so was quite surprised at how well things worked out for me at college, I put a lot of it down to one or two (maybe three) lecturers that had a certain teaching style that certainly worked for me. I then started to get into it and in the main enjoyed it. But I do think the way we were trained had a way of getting the knowledge into a learner. Certainly doesn’t seem to be the case now... I am not surprised to hear you were with SEEBOARD. I knew quite a few electricians as well as managing engineers from SEEBOARD and generally they were all well trained and knew their onions. In fact my two main sparks were SEEBOARD electricians who were suconded to the firm I was working for in Middlesex/ Surrey... Small world. Keep up the great work.

[@angelofranklin1]

brilliant expalation

[@jameselliott7114]

Great video. Not really done any calculations since college in mid 90s so trying to get up to speed with it all again now im self employed

[@cestemshow]

Really happy it helps, more on their way, just full time teaching gets in the way 🙄😉

[@adamcleverly310]

Never been taught so well! thanks

[@cestemshow]

Our pleasure!

[@pjw6961]

Great video. Got me up to speed again. Thanks.

[@cestemshow]

Thank you! Always happy to help!!!

[@zakkent3352]

Hi, I currently doing the coursework section of the 2396 Desgin and Verification. At this moment I am undertaking the calulations for the themal constraints for all my cuircuits, but from when I did the course, I seem to have notes that apply a Cmin or Cmax factor to the Uo (Voltage) when calculating the fault currents dependant on which calculation is being done (cant remeber which way round is correct). I think one requires the Minimum Fault Current (using Cmin of 0.95 and Zs @ 70/90degree) and one requires the Maximum ( using Cmax value of 1.1 and Zs @ 20Degrees). Have I got this incorrect? You show in the video that both the Fault currents are calculated using the nominal voltage (230V) and the Zs @ 70degrees. Thanks for the video, it has been very helpful!

[@cestemshow]

If you used Cmin with max Zs then you would get a lower fault current so yes you're right you would add Cmin to Uo to get worst case scenario. if that current activates the solenoid of the protective device then 230v would as would any other higher voltages. These videos are for my apprentices initially and just to get the concepts but IET design guide section 8 discusses it. So, when calculating S= you would use CminxUo/Zs@70 degrees and you would use Cmax x Uo/Zf for obtaining fault current when using it as t= another way of putting it is Cmin for max disconnection times stuff and Cmax for max fault currents for short circuit stuff. I would def recommend the IET design guide for the 2396. Good luck with your project :-)

[@gpoulitsis]

Great video! Thanks!

[@cestemshow]

Glad you liked it! Thank you!!!

[@johnpeat1398]

great video, made it all very clear

[@cestemshow]

Glad it helped!

[@topspark7688]

Brilliant video Craig. 😃

[@cestemshow]

Thanks 👍 Glad you enjoyed it.!

[@cestemshow]

And yes I did spill tea on my notes hence the silly faces.

[@RedaReda-uk9lm]

Thanks you made it simple. Now make sense for me.

[@cestemshow]

You're welcome! Glad it helped

[@KP-ug4kr]

Thank You this helped me alot

[@cestemshow]

Glad it helped

[@napath6005]

Thanks for this

[@cestemshow]

No problem

[@ef7480]

5 thumbs down? Weird....

[@cestemshow]

Not really surprised. There are some real children in the electrical industry who like to troll.

[@garethatkinson7765]

No need for the "x".

[@cestemshow]

I know, but some get confused when left out..... This is for level 3.....

[@garethatkinson7765]

@@cestemshow i know you know. Your certainly more competent then me.

[@cestemshow]

Just a nerdy Sparky at the end of the day like all of us. Just been interested in taking things apart since I was 6....blew myself up a few times too.... Which taught me about charge flow 😂👍