MY FUSE SIZE IS NOT LISTED IN THE REGS BOOKS - HOW CAN I FIND ZS FOR THE CIRCUITS I AM WORKING ON?

In this LearnElectrics video we look at how to find a Zs value or Earth Fault Loop Impedance, when the fuse size that you need, for the disconnection time that you need, is not shown in the Regulations book. And in this video, we will make reference to Amendment 2 of the Wiring Regulations, the brown book.
A question that is often asked on social media states that the fuse size for which a Zs is needed, is not listed. How can I find the Zs for my test results?
And a question that was sent to me by email ..
I have a BS88-3 system C fuse at 80 amps and I need a Zs value for 0.4 seconds disconnection time.
The fuse size is not shown in table 41.2 of the Regulations book, what can I do?
The video begins by looking at this last question and then works through several other examples, showing you the method and the calculations to arrive at the correct answer.
Also, the LearnElectrics video shown on the following link will give further information about tabulated and measured Zs values, and that all important 80% rule.
THE 80% RULE - Zs MEASURED - Zs TABULATED - WHAT IS THE DIFFERENCE? - WHICH ONE TO USE WHEN AND WHY
• THE 80% RULE - Zs MEAS...
This is video number 238 and to view all our videos type in LearnElectrics all one word into the UA-cam search bar.
Visit our UA-cam channel where we have many more videos on a wide range of electrical topics.

[@cminuets6859]

Dave what you are doing on this platform is absolutely fantastic. I have learnt so much that I will buy you a drink when I pass my 18th edition and secure my next job

[@learnelectrics4402]

Keep learning, its a great trade to be in. It's taken me around the world several times.
Learn a little every day, at the end of the year you will not be the same person.
Good luck. Make mine a pale ale.
Dave.

[@Harrycowlton]

Think you mean divide by 800 not 750. But as ever, brill video!

[@learnelectrics4402]

That's it. My typo. Thanks for watching. Appreciated.

[@gbelectricks]

Brilliant explanation as ever Dave, thanks for sharing👍👍

[@learnelectrics4402]

Very welcome, thank you. Dave.

[@francoistoumany3841]

Thanks for the information as always Dave, helping us to keep a step ahead👌🏾 Hope the treatment went well! 🙏🏽

[@learnelectrics4402]

Thanks for the support, appreciated. Long job I'm afraid. Just had another week of it. I'll beat it. Thanks for asking.

[@phunkyphantom619]

The table shows 800A for a disconnect of 0.4s, where did you get 750 from? That will give a longer delay time between 0.4s and 1s. Also the table at 11:09 has different values to ones you've just shown? You showed 100A needed an Ia of 1200, why are we now calculating for 1000A?

[@matt_b4865]

Also confused by these values that were chosen to do the sums?

[@no_short_circuit]

Me too!

[@nkdarren1225]

Whilst the first example is a little bit confusing to me, using the formula given and the values needed to obtain a 0.4 second disconnection time, I was expecting something along the lines of Zs = 230v x0.95 /800 = 0.27 or 0.273125 (If you really want to be precise) but 750 Ia? I'm not exactly sure where that number is coming from since it is not in the table. Could just be a simple mistake that can easily be corrected. However, to the second part of your question, the Ia for a 100A System E and G fuse is 1000A, not 1200. That is for a BS 3036 Fuse which is different to the BS88-2 system E and G. If you wanted a 0.2 disconnection time with the BS88-2 system E and G then the Ia for a 100A rated fuse would be 1200A. Hope this helps.

[@elijahkalonji7522]

He made a mistake, was supposed to write 800.

[@learnelectrics4402]

Yes, I should have written 800A. It was along week on the cancer treatment. Thanks for the heads up, appreciated.

[@azizurrahman6663]

800A but you calculated 750A how it work can you explains please dave.
Very nice video thank you again and again

[@learnelectrics4402]

My typo, should be 800A. great that you spotted that. Dave

[@benYMSB]

Hi. My main fuse is 80amp. Just worked out my maximum demand and it’s coming to 102.4. I’m currently building a portfolio so it’s got to be by the book so what is the procedure for this issue? Many thanks.

[@learnelectrics4402]

Don't forget about diversity, take a look at this video.
ua-cam.com/video/TV2IZtmydm4/v-deo.html

[@user-qi8tv2sj4m]

👍thankyou

[@learnelectrics4402]

Very welcome. Thank you.

[@JJ-yt8ww]

P r o m o S M

[@learnelectrics4402]

Thanks for watching.