Zs - TABULATED or MEASURED. An easy method to calculate the Zs values without the books.
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- čas přidán 27. 07. 2024
- We are sometimes asked about so called magic numbers, those numbers that will allow us to quickly calculate and determine certain electrical parameters without the need to start searching through many pages of the Wiring Regulations or the On-Site Guide.
So here we have looked at two such numbers that will help us to quickly establish Zs values for some of the common circuit breakers in use today.
We also look at whether we need to determine the tabulated values or the measured values, and what exactly is the relationship between these and why have two different numbers?
Once you understand the basics of this method, you will have acquired a new skill for life and leaving your books at home will no longer be a problem, in a matter of seconds you will know the Zs numbers to measure against during your testing.
You may also want to view the following LearnElectrics videos which are related to this topic …
This video is No.100 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.
To go directly to our LearnElectrics Channel on CZcams
Click on the link below …
czcams.com/channels/YaJQnpO4XAp0yCgqzMkmfA.html
Dave is brilliant teacher/mentor. He explains topics extremely well and breaks down things in order for you to understand easily.
Thank you Abdirizak. I really appreciate your comments. Dave.
Thanks for the video. As I've said before, I'm not qualified but still learning. I watched your other video on "35" and was helping a mate of mine who is an electrician and he couldn't believe that "it actually works!" and he's been a sparky for 30 years.
There we go. You are now a Wizard in his eyes. It's the little memory joggers that make the job so much easier, especially for folks that are learning 18th Edition. Stick with it, it is a great trade to be in at any age, it's taken me all around the world over the last 40 years. The most important thing is your attitude towards learning. If you want to learn, you will.
Keep going, good luck, Dave.
Thanks very much, listened to your videos to help with my 2391 online exam resit, passed this morning after anxious revision at 5am headphones on studying your CZcams posts- appreciate you sharing this information, regards Paul
Fantastic news. So glad you passed. If the channel helped you, then please spread the word and help others to pass.
Keep learning. Dave.
Love these videos so much… really working wonders with my training. I’ve subscribed. Keep up the good work mate! Whoever you are! You’re a great teacher!
Brilliant feedback, thank you so much. Dave.
i was really struggling with zs measured and tabulated until i saw these videos. thanks for all your help, i have my 2391-52 next week so will update!
Glad it is useful and good luck. Dave.
Thank you for very easy and simple way to explain electrical. Many many thanks 😊 🙏
You are very welcome Amir. Thanks for watching. Dave.
Thanks Dave. Excellent presentation.
Thank you David, much appreciated comments and glad that they are useful. Dave.
Super and very well explained thank you, to date i think i have watched all your vids. All very good.
Thanks Angelo, your support is really appreciated. Dave.
Super very well explained. Thanks you so much.
Thank you Dinesh, trying our best. Thanks for watching. Dave.
This is fantastic! Thank you very much.
If it helps, great. Thanks for the positive comments. Dave.
Probably the most useful CZcams video any electrician could watch! Any chance of some more 2391 related videos please 🙏🏻
Certainly Justin. I try an make the Thursday videos relevant to exams, calculations etc. keep watching, lots to come. Dave.
Great video once again mate👍🏻
Thanks Dibbo, appreciated. Dave.
Thanks very much.
You are very welcome. Appreciated.
Brillent as usual!
Regards mg.
Thanks for the ongoing support Malachy, really appreciated. Dave.
Hi Dave thank you very much very nice , please do more video it very helpful
Absolutely will Azizur. Next weeks video is about fault finding on a socket ring circuit. Thanks for watching, thanks for your support. Dave.
Thank you ❤
Appreciated. Thanks for watching.
brilliant, thankyou
Thanks Brian, thank you for watching. Dave.
Very helpful 👍👍👍
Thanks Michael. I appreciate your helpful comments. Thanks for watching. Dave.
Wonderful
Thanks for the comment and thanks for watching. Dave.
Dave-work of genius.. super well explained-as usual. Do you have any quick methods for working out the maximum demand?
Paul, no magic numbers but have a look at the video shown below. Max demand is very easy to work out and the video takes you through several different scenarios. Dave
See Diversity and Maximum Demand on this link ...
czcams.com/video/TV2IZtmydm4/video.html
Thanks for another excellent video.
Thank you Mark, appreciated comments. Dave.
My pleasure Mark.
Hi dave I've been watching your videos for some time now they're very useful but one thing I'm struggling with the difference of the Max Zs tables of 0.4s and 5s disconnection time, if you could explain that'd be great help and much appreciated thank you.
Ricky have a look at this video about final (0.4s) and distribution (5s) circuits
czcams.com/video/Jsqx7b9VdyM/video.html
Note that this has the old website address on it (dot co dot uk) which is now a dot com address.
Another video on final/distribution circuits is planned for the near future too. Watch this space. Dave.
Hey agree, this is a way of calculating Zs but in my opinion it doesn’t give you an understanding of the whole thing and how its actually. Calculated in BS7671. Which isn’t that much more complicated. All thats needed is 3 to 5 x In for B types, 5 to 10 for C types and 10 to 20 for D types. This allows you to understand that a breaker has a range it must trip within. As we’re looking for a worst case for maximum Zs you use the higher value.
Eg 32A MCB B type would be 32 x 5 = 160A. Using Ohms law 230V / 160A =1.4375ohms. Using 0.95 correction for voltage fluctuation Cm 1.4375 x 0.95 = 1.37 ohms. Simple
Thanks Jon, yes, we already have a video on how it is calculated from the time and current tables and this is another interesting method. Thanks for watching, thanks for your input. Dave.
Why bother when shorter and easier method .
Hi I am doing 2392 on line goal exam, any things special I should know about it?
Just practice lots of questions, a few every day. Actually write the question and write the answer. make sure you are good on calculations. Have a look at thie video below. also go to LearnElectrics.com and put 2391 or Amendment 2 into the search box. Loads of videos with questions and answers in the exam style. Good luck.
czcams.com/video/FIYPvQk55NA/video.html
Hi Guys
Have you got any book or would you publish a mini book yo carry in pocket, simple as you explain on CZcams? It would be fantastic idea for many learners or even professionals
Amir, great idea. one or two others have asked, perhaps I should consider it, if it would sell.
Boss
Thank you Jack, thanks for watching.