THE 80% RULE - Zs MEASURED - Zs TABULATED - WHAT IS THE DIFFERENCE? - WHICH ONE TO USE WHEN AND WHY
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- Опубліковано 5 січ 2024
- This LearnElectrics video looks at Zs measurements that we might make when on site and considers the so-called 80% rule. Something that we should all know and use.
For some, including new learners, there can be concern over which numbers to use when testing and making out certificates and there can be some confusion over what the different figures actually mean.
This is an update to an earlier video on this subject, from a few years ago, and all references made are now to the brown Wiring Regulations book - BS7671 : 2018 - Amendment 2 : 2022
What is the 80 percent rule?
It is a method used to calculate the measured Zs values for different sizes of circuit breakers and fuses.
The measured values are those that we will measure when on-site and when testing circuits with our test meters and multi-function testers.
So, what does it actually mean? Show me the 80% rule?
And we start with covering a few basics, to clear up any confusion that there may be, and then look at the what, why and how of Zs and the 80% rule.
This is video number 233 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.
What a great video. Love learning the theory! Makes perfect sense! 👍🏾
Glad you enjoyed it, thank you. Dave.
Another video, and another clear and concise explanation! Thanks for all your efforts Dave. You really should consider teaching as a profession!😁👍👍👍👍
Thank you. I'm trying to retire. Dave.
This is a very good video on the 80%rule (again) I saw the other one and brought it up in college but no one really wanted to know. Well it did come up in the 2391 exam. I got the top mark
There we go. You made the effort and you got the rewards. Keep spreading the word, somebody may listen and benefit from it. Thanks. Dave.
Great video, shared 👍
Thank you Chris, appreciated, Dave.
Brilliant
Thank you, appreciated.
Brilliant summary of older videos. Thanks! Is it new regulation of disconnection time 0.1s, instead of 0.4s?
0.4 is maximum permitted
0.1 is considered instantaneous and is the target
See the attached comment. Perfect explanation. Modern MCBs will achieve 0.1s which easily covers 0.4s. Same regulations, just better response times on newer devices.
Thank you, excellent support. Dave.
Thanks dave
My pleasure, Thanks for watching. Dave.
As a DIYer with a background in computer electronics, I would love to know the route to take so I can effectively be on a approved person scheme as a domestic installer, so I can sign off my own work such as house rewire or replacing my CU. I want to do the 18th Ed, Part P, testing PAT courses and be in a position so not need to go through building control, does such a route exist with the few of us DIYers with too much free time and money to throw at courses but not interesting in being a Tradie or running a business?
Whatever route you take you will need to jump through certain hoops, practical skills, theory skills, evidence of capability and much more. There is no short cut, its a skilled profession. Visit at least 3 training centres and talk with them, don't do it on the phone, actually drive there and see what you are getting for your hard earned cash. Do not part with any money until you know exactly what you are getting and you are happy with the time frame to be competent and registered. Also look at Napit website and NICEIC website.
Good luck
Thank you. Dave.
C Min... 😉
Yes, an important one to remember and sometimes comes up in 18th Edition exams.