WHAT IS Zs? Why is it important to test Zs.

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What is Zs, what is it made up of. We look at the different parts of a circuit, Ze, R1 and R2 to understand what is involved in the testing. How much current can flow, what is a fatal electric shock and how does a correctly wired electrical system prevent this. Understand the difference between an impedance and a resistance, understand why a disconnection time is specified. A short and to the point video that will help you to understand this fundamental test for safety.
To view all our videos, click on the following link
/ @learnelectrics4402

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4 июл 2024

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Комментарии : 117

@learnelectrics4402 3 года назад

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. ru-vid.com/show-UCYaJQnpO4XAp0yCgqzMkmfA

@rri7534 3 года назад

The most understandable explanation of zs I have come across, Thank you for your time & effort in making this available, will help me loads towards passing the 18th Edition exam, God bless you 🙏🏽👍🏻👏🏻👏🏻👏🏻👏🏻

@learnelectrics4402 3 года назад

Thank you so much for the great feedback. Lots more to come, including tips on the 18th Edition Exams and using the Regs book. Spread the word, the more that know about our channel, the more videos we can make. Dave.

@multirole240 3 года назад

Thank you for an excellent straight forward understandable presentation, well spoken at a sensible pace.

@learnelectrics4402 3 года назад

Glad we could help. Many thanks. Dave

@lcutz9854 3 года назад

What an excellent video! Best explanation so far I’ve seen on RU-vid 👍

@learnelectrics4402 3 года назад

Thank you for the positive comment. We try our best and comments like this make it all worth while. Bux

@tomb3175 2 года назад

I agree with others. This is the best straightforward explaination on RU-vid.

@learnelectrics4402 2 года назад

So glad you found it useful, really appreciated. Dave.

@rezamaddah2010 3 года назад

Just I want to say all about electrical describ are complete and clear and I learn to get many information that I didn't know.God bless you.thanks.

@learnelectrics4402 3 года назад

Thank yo Reza, very kind words. Lots of videos to watch and lots more to come. Dave.

@chrischaralambous286 2 года назад

Thank you for this crystal clear explanation. This video has been very helpful. I have watched a couple of other videos from Learn Electrics and would just like to thank you for explaining things so clearly and making it so much easier to understand.👍

@learnelectrics4402 2 года назад

Brilliant feedback Chris, thank you. Dave.

@hussmortada Год назад

Thank you very much, a clear and easy to follow explanation. I always benefit from your videos and enjoy watching them. Thank you again

@learnelectrics4402 Год назад

Thanks Hussein, and thanks for supporting the channel.

@Michael-xk9ft 3 года назад

Thanks you, a nice useful recap. I hope more like this will be coming. Cheers

@learnelectrics4402 3 года назад

Thank you for your comments. We try to use our experiences of all the questions we are asked over the years. Certainly there will be more to follow. Every Monday we upload a new video. Thanks again, Dave.

@Andrew-hu9ke 2 года назад

Excellent as always, Thank you 👍😎

@learnelectrics4402 2 года назад

Thanks Andrew, I appreciate the support. Dave.

@rizgar8121 9 месяцев назад

Thank you Dear, for all this understandable lessons.

@learnelectrics4402 9 месяцев назад

Glad it was helpful and thank you for watching. Appreciated. Dave.

@alvarob2443 2 года назад

Love this videos, specially now that i started doing testing

@learnelectrics4402 2 года назад

That's good, glad you are finding them useful. Lots more to follow. Dave.

@pinchermartyn3959 2 года назад

Just excellent. Thank you.

@learnelectrics4402 2 года назад

Great feedback, thank you.

@MobiletentedcampsZa 2 года назад

Brilliant as usual.

@learnelectrics4402 2 года назад

Great feedback, thank you very much. Dave.

@cobydavies5304 3 года назад

This was quality thank you

@learnelectrics4402 3 года назад

Thankyou for your comment. Glad you liked it, we try our best.

@alikhalfa4932 5 месяцев назад

Thanks a lot for a clear and fully understandable method of teaching , i spent 3 years in college couldn't understand properly the principle of ZS till now .

@learnelectrics4402 5 месяцев назад

Glad it helped. Dave.

@alig7800 3 года назад

THANK YOU MADE IT EASY TO UNDERSTAND

@learnelectrics4402 3 года назад

Thanks for the great comments.

@paulward143 2 года назад

Brilliant very clear.

@learnelectrics4402 2 года назад

Thank you Paul, appreciated comments and thanks for watching. Dave.

@trebushett2079 2 года назад

Excellent and informtive channel.

@learnelectrics4402 2 года назад

Much appreciated Tre. Thanks for watching. Dave.

@dascarcatumbela4084 2 года назад

thanks for good lesson

@learnelectrics4402 2 года назад

Great feedback Dascar, thanks. Dave.

@2207amin 2 месяца назад

I like ur simplicity in ur answers. Its v good when u start from basics. Thanks 🎉🎉🎉❤❤❤

@learnelectrics4402 2 месяца назад

Thank you so much, great comments, appreciated.

@danielteyehuago1633 Год назад

Wow! This is very informative, thanks for sharing it with us. It worth it and the best tutorial on the topic for me...dl

@learnelectrics4402 Год назад

Thanks for the support. Dave.

@shahzadhameed3741 3 года назад

Excellent

@learnelectrics4402 3 года назад

Thank you for the positive comment. Appreciated. Dave

@slapman7646 2 года назад

Thank you.

@learnelectrics4402 2 года назад

You're very welcome. Dave.

@IFICANDOITYOUCANDOIT1979 3 года назад

BIG THANK YOU

@learnelectrics4402 3 года назад

Great feedback and much appreciated. Thank you. Dave.

@ranat5526 3 года назад

Thank You.

@learnelectrics4402 3 года назад

Thanks for the comment, glad you liked it. Lots more to come. Bux

@mdmvukengineer4873 2 месяца назад

Excellent 👍

@learnelectrics4402 Месяц назад

Many thanks. Dave.

@user-in6lf9jk3d Год назад

tank you for the nalelge that you give as.

@learnelectrics4402 Год назад

Glad that you find it useful. Lots more to come. Dave.

@Ibrehas 10 месяцев назад

simple and precise just wanted to know what you would set your multimeter to when measuring the ZE and R1 + R2

@learnelectrics4402 10 месяцев назад

You can use a multimeter for R1+R2 but you will need a multifunction tester for Ze and Zs. Hope this helps. Dave.

@hakeem2006 3 года назад

Excellent presentation. Please can you explain how do we achieve the 100amp fault current to flow to trigger the MCB to trip @ 0.4 second! Knowing appliances don’t required that much amperes to start or run on full load. Forgive my ignorance if have asked an obvious question! Regards

@learnelectrics4402 3 года назад

It is the earth fault path having a low resistance that allows a large fault current to flow. The fault path is Line and Earth, not Line and Neutral Its all to do with Ohms Law, if the earth fault path is low enough then the current will be high. Some of our other videos will help you to understand this better, especially our video on Ohms law.

@daviddmf 7 месяцев назад

Thank you for this. What causes the faulty circuits mcbs to trip rather than the other mcbs in the CU? The incoming supplys Line and Neutral are two incoming supply conductors. If there is a fault a surge of current will loop round from the consumer to the transformer and back round to the consumers CU. How does a single MCB know when to trigger when all the MCBs in the CU are also exposed to the fault current surge coming in from the Supply?

@learnelectrics4402 7 месяцев назад

Because the fault current has to pass through the mcb of the faulty circuit. It doesn't matter what is happening on just one side of the fuse or breaker. Watch this video, it will tell all. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-FZ6-okbgXKo.html

@crazyivan52 2 года назад

I have a question. In a phase - neutral short circuit fault with no grounding what is the fault loop? From the neutral to the trasformer or to the electrical meter?

@learnelectrics4402 2 года назад

It's the whole loop through the transformer and back. Have another look at the video. Thanks for watching. Dave.

@jmphotography205 3 года назад

as dyslexic , can i ask you to add subtitles to your videos ,will make me understand you better thanks .love you work cheers

@learnelectrics4402 3 года назад

Joanna, that is something that could be considered in the future. Thanks for getting in touch and good luck with the learning. Dave.

@faisalahmad4232 Год назад

Will the reading be effective if i use a temporary generator connected to the earth rods during testing and commissioning instead of the transformer ?

@learnelectrics4402 Год назад

If the installation is to run on the national grid, you really need to test it when connected to the grid. Your generator will give different readings. You can test R1+R2 as a dead test and add to an assumed ZE (0.35 ohms for TNCS). When the DNO connects up, the Ze will usually be less than 0.35 so your Zs figures will be acceptable. Hope this helps. Dave.

@matthewdaniel1715 Год назад

A masterpiece

@learnelectrics4402 Год назад

Thank you Matthew, appreciated. Dave.

@kaybhee6 Год назад

keen

@learnelectrics4402 Год назад

Glad to hear it, thanks for watching. Dave.

@westwonic 2 года назад

Great explanation, but I have one question; If the lowest resistance possible is required for the earth conductor ( to achieve higher fault current), why is the cross sectional area of the earth conductor in 2c+e cable smaller than the line or neutral conductors?

@learnelectrics4402 2 года назад

Good question Nick. It's all to do with the Adiabatic Equation and the time for the fuse or breaker to trip. We can put any bigger size earth in we want but if its not going to overheat before the fuse blows then why waste copper (and money). Have a look at this video, it explains it all. Dave. 18th EDITION - SESSION 4 - ADIABATIC EQUATIONS, click on the link below ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-173C7yE-xbU.html

@zulfakarali6274 3 года назад

Thanks

@learnelectrics4402 3 года назад

You are very welcome. Glad we can help.

@amriabssamad4695 3 года назад

Thank you for been much clearer in your explanation

@learnelectrics4402 3 года назад

Happy to help and thank you for the positive comments. lots more to come. Dave

@atifmughal1905 Месяц назад

Hi Dave, Thank you for the great content as always. Amazing work and information provided. I wanted to ask a question, why would the RCD trip when ZS testing and I get no reading. Please if you could have an idea of what this could be? Thanks

@learnelectrics4402 Месяц назад

If you have your test meter set to the normal Zs test this will happen. Set your test meter to the NO-TRIP setting and it should clear this. Different meters mark the no trip test differently so check the user instructions with the meter or go online to the manufacturers website. Take a look at the video on this link, its an old one of ours, but it will help. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-n1XSSSs5ILo.html

@atifmughal1905 Месяц назад

@@learnelectrics4402 thank you for your reply and your time. This property is the only one that gives me a problem - testing other properties with the same tester I’ve never had this issue. The setting is always set the same way but it only seems to be happening at this property. Just abit baffled as to why this is happening here. The tester is Megger MFT1721 Thanks

@ciaranhughes8705 2 года назад

Great video. Just a quick question. My fluke requires me to have all 3 testing cables connected to undertake a Zs test. If it's only testing through line and earth why is the neutral required to complete the test. Sorry if this sounds daft but just interested after watching your explanation.

@learnelectrics4402 2 года назад

Not daft at all. The meter tests between phase and Earth but it also needs a neutral connection to make the meter work, for example, just like a kettle needs the neutral connected. Some modern two lead meters actually make an internal link between N and E and on some you can hear the relay pull in if the room is quiet. Hope this helps.

@yanalnaghawai1872 9 месяцев назад

Hello Dave, please be patient with me, A 20A breaker needs 100 amps to flow .. etc, i can't understand from where the 100 amps will come, can you please explain to me or tell me which video i must see to understand this

@learnelectrics4402 9 месяцев назад

Have a look at the two videos on the links below, they will hopefully answer your questions and help you become expert. Remember that we are interested in two different currents in a 20A fuse or breaker. The 20 amps working current, day in day out; and the 100 amps fault current that causes almost instant tripping to keep people safe, Enjoy and keep learning. Dave More magic numbers ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-l0y8gtfUj_k.html Why my fuse blows ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-FZ6-okbgXKo.html

@user-fx8dy2fw5y 2 года назад

Great content. Why is the loop impedance value not the same in Table B6 the onsite guide to BS 7671 table 41.3. B type mcb 20 amp. I know in BS 7671 there is a factor of 0.8 and in your video you mention the value must be below 1.75 ohm. the value in BS7671 says 2.19 ohms. I hope this makes Sense.

@learnelectrics4402 2 года назад

Good question. That is the 80% rule. take a look at our video ZS and the 80% Rule on this link. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ihD-NO-7G5Y.html Thanks for watching. Dave.

@michaelcostello6991 3 года назад

Why do we not calculate the impedance of the Live/Neutral circuit also ? to ensure breaker trips in time allowed in event of a short etc etc

@learnelectrics4402 3 года назад

We do measure it, but its not recorded the same as R1+R2. PSCC is your test for shorts. Hope this helps.

@gd-bq7em 10 месяцев назад

If the zs on a b32 mcb is 1.10 max on a tn system and the reading was coming back higher, would this circuit require rcd protected to provide fault protection, would it then be acceptable or not,

@learnelectrics4402 10 месяцев назад

The Regs do permit that under certain circumstances but first look at the options available to bring Zs in line. Have a look at this video on the attached link. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-fUlCDhlcDf4.html

@TheNathan696969 9 месяцев назад

As a Mechanical engineer that has just progressed into commissioning and consultancy, your video has been very informative and totally understandable! however, I have a question, could an on site guide values deviate from a standard Zs table and if so why?

@learnelectrics4402 8 месяцев назад

Have a look at these 3 videos, less than an hour in total. They will really boost your understanding. The OSG uses 80% values based on the 100% values in the tables in the Regulations book. An, there are some typos in the OSG tables, highlighted in the videos. Thanks for watching. Dave. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-QWr-ilqW67A.html ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-fkSUrz0HaPE.html ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-nVZeIFeEwl0.html

@TheNathan696969 8 месяцев назад

@@learnelectrics4402 ohh great, thanks a lot :)

@ja_adam_ 11 месяцев назад

Hi, Need help with this please Max Ze for TNCS is 0.35.... What happens when you then have large protective devices for outgoing ways. For example perhaps the consumer unit is more than 3 meters away so you have to use a 100A bs88 fuse.. same for blocks of flats.. this has a max ZS of 0.34.. if the Ze is close to maximum, how on earth are you supposed to get round it?

@learnelectrics4402 11 месяцев назад

If Ze is close to the maximum, then that is still ok. Also consider what the Zs readings are, they are the important ones.

@ja_adam_ 11 месяцев назад

@@learnelectrics4402 that’s what I mean …if I have a 160A BS88 max ZS is 0.34 ….. what if my ZE is 0.34?!

@anelectrician 2 года назад

06:48 Dave here you're demonstrating a fault at the kettle. Therefore the fuse on the kettle should be the focus and not at the consumer unit.

@learnelectrics4402 2 года назад

Thanks for watching, appreciated. Dave.

@Wanderers-Bulgaria 2 года назад

A question: - if the resistance of a human touching the energized kettle is greater than the Zs, will it receive an electric shock? Perhaps the Zs is more about protecting electric installation and less about human protection 🤔. RCD is the device that is more about direct human electric shock. Great video though 👌

@learnelectrics4402 2 года назад

The human body would form part of a parallel path with the kettle. Thanks for watching. Dave.

@Wanderers-Bulgaria 2 года назад

@@learnelectrics4402 I am not sure, because the metal frame would have lower resistance than human body, and thus the current would flow through the frame and not the human body. Do you agree?

@tommylau7457 2 года назад

I want to know how to calculate the time to burn a fuse given the material, temperature, thickness of the fuse, and the current passing through it. I tried finding fuses online and very few places have graphs that show the curves (for example generators often have discharge graph with curves)

@learnelectrics4402 2 года назад

Tommy, not really something we worry too much about as electricians. We work from a set of approved fuses and breakers and all the calculating of burn time, material etc is done by the manufacturer. You may find the data that you want on a fuse manufacturers website, but then again, they may keep the information secret. Thanks for watching. Dave.

@tommylau7457 2 года назад

@@learnelectrics4402 i see, so is so many product manufacturers, even for cars, most of the time they base on the previous products rather than doing a whole new set of calculations, probably 95% empirical.

@tommylau7457 2 года назад

@@learnelectrics4402 or idk if the deviation is too high, the rate of failure is too high, like long HDMI cables, that could also be a reason

@PhuongLe-bf8ym 2 года назад

how did you do it can you share with me , thank you

@learnelectrics4402 2 года назад

It's just repetition and practice. The more you install and test circuits, the more you learn. Good luck. Dave.

@jonw2570 Год назад

What happens in a short circuit? If in an earth fault the current flows through the earth and back through the mcb. In a short circuit if it flows through the neutral to neutral bar, how does it go back through the mcb to trip it? If it goes back to transformer and then back through to mcb, how come we don’t do a “neutral fault loop” test

@learnelectrics4402 Год назад

Earth and neutral are effectively the same point back at the transformer. Earth fault is L+E and short circuit is L+N so neutral is covered. Thanks for asking, thanks for watching.

@jonw2570 Год назад

@@learnelectrics4402 thanks for the reply! Does that mean in a short circuit the fault current flows down neutral to transformer and back through the L through the MCB causing it to trip… or …. Does the fault current through the L conductor increase due to the fault causing mcb to trip.

@markpalm672 Год назад

Dear sir, thanks for your great presentations. But in another video , if am not mistaken it was said that for type B we need Zs to be not more than 3.5 Ω and not 1.75 Ω. What is correct?

@learnelectrics4402 Год назад

Both are correct Mark. A 10A Type B has a max Zs of 3.5 ohms whilst a 20A type B is 1.75 ohms. Hope this helps and thanks for watching. Dave.

@markpalm672 Год назад

@@learnelectrics4402 Great Dave! Thanks for your prompt reply.

@dennisfowler7873 3 года назад

Hi sir... im searching for an answer regarding ZS...wat would cause my measured ZS to be lower than my calculated ZS ... zs = ze + (R1+R2)

@learnelectrics4402 3 года назад

Measured and calculated are never the same. For a start Ze is a live AC measurement, and R1+R2 are DC dead tests. Different switch settings on your meter and so slight differences. How good are the batteries, how hard are you pressing the probes, what is the temperature in the room. Are there parallel earth paths, is it TT or TN. Lots of things. If they are close don't worry about it.

@dennisfowler7873 3 года назад

@@learnelectrics4402 thanks sir

@learnelectrics4402 3 года назад

Happy to help.