TESTING Ze Zs UNDERSTAND THE DIFFERENCE BETWEEN Ze AND Zs AND HOW TO TEST CORRECTLY
This video is all about how to test the impedance of electrical circuits correctly.
We must be able to understand the difference between Ze and Zs and be able to identify which parts of an electrical circuit they relate to.
It is essential that all electricians understand what these two values are, how they relate to the Zs tables in the Wiring Regulations and On-Site Guide, and ultimately how they can have a major impact on the health and safety of the users of the electrical system and occupants of the building.
Get this right and you can confidently sign off and certify your work with respect to electrical disconnection times for fuses and breakers.
The video deals with a must know piece of information, a fundamental requirement for all electricians.
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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. kzhead.info/tools/YaJQnpO4XAp0yCgqzMkmfA.html
Very well explained. Thanks for all efforts.
Most welcome, thank you. Dave.
Brilliantly said thanks 😊
Thank you, great feedback. Dave.
Great vedio many thanks for your explanations.
Thanks Mohamed. Great support, appreciated,
Wow! This is very informative, thanks for sharing it with us. It worth it and the best tutorial on the topic for me...dl
My pleasure Daniel, thanks.
YES YOU HAVE ADDED MORE DOWN TO EARTH 🌎 KNOWLEDGE . MIGHTY THANKS . L.A.M
Great feedback Lloyd. Thanks for the support. Dave.
Brilliant man
Thanks. happy that you found it useful and lots more to come. Dave.
well explained, more clear than college
Thank you Bledar, appreciate your positive comments. Lots more to come, spread the word around the college, the more that view our videos, the more that we can make. Dave.
Great video as always .Didn't know you did 2 x Ze tests, the second after reinstating the earthing conductor ..makes sense.Learner question: Do you leave luminaires IN or OUT on Zs Live test.If IN would you leave all switches ON to those luminaires,when testing furthest S/L and cpc.(i appreciate you are encouraged to do this by calculation).Thank you again
Zs is a live test so it will matter not if the lights are on or off. Just try and test from the furthest electrical point which isn't always the same as the furthest from the CU. Thanks for watching. Dave.
Please will you make a video on Pfc ,Pefc testing and recording on a 3phase installation. It is unclear when doubling the measurement of either if the Ze should also be doubled or not.
Great idea Ruben. It will be done in the next week or so. Thanks for your valuable input.
Thanks for the explanation. Why do the Certificates ask for Zs at the DB instead of Ze?
Good question. There is only one Ze in a property. But there can be one or more CUs from the first consumer unit. The first CU has the real Ze and all the others CUs are actually Zs but they are acting as a Ze. So there is no confusion they are all called Zdb on the certificate = the Z at the distribution board or consumer unit. You the electrician then decide if it is the real Ze or a Zs acting as a Ze. Hope this helps. Dave.
@@learnelectrics4402 that does really help. Thanks for clarifying. I appreciate the answer
It confuses a lot of people but actually makes sense - but only once you know. Dave.
Where do you take a Ze in a hospital or large building then, youd never be able to isolate to remove the earth from the met
In a 400Vac Electric Motor the Zs Loop will be misured with load or whiout load. I mean the Zs loop need to be check with wire connected to the motor or disconnected from the motor? Thx
You will need to disconnect the motor or isolate nearby to check each phases Zs, IPF etc. Thanks for watching. Dave.
So measured Ze is most likely to be lower when the suppliers earth is connected to the earth bar, due to the parallel paths. Why then consider the Ze at the earth bar? Perhaps if we are expecting parallel paths due to gas or water bonding but don’t see a lower Ze, we can deduce that those bonds are deficient (need investigation) or are obsolete (plastic pipe). We should be measuring the resistance of those bonds separately in any case?
We just follow the testing sequence as per the IET recommendations and the schedules of inspections and tests. We should definitely test the main bonds separately with one end open so that we know we are testing only that particular bonding cable. Good points. Dave.
Regarding calculation of r1 plus r1 with zs or ze given how can it be done
That is an excellent request for a video. There are some very useful formulas for this and I will do a video on it very soon. Too long to put into comments. Watch this space, and thanks for watching the videos. Dave.
@@learnelectrics4402 thankx for the reply....im a upcoming electrician doing nvq on independently and finding source material is difficult....I may make my own vids in future....your channel helps me better understand electrics👍👍👍
We measure R1+R2 at installation stage. Is that correct ? Is there a max R1+R2 value allowed. How do we know the reading is acceptable. When we measure Zs < 0.35 ohm the power is turned on.
Michael, have another look at the video and also look at these three videos as well, together they will explain the whole thing, and more. All learning takes time, we’ll get you there. Good luck and thanks for watching. Take a look at these three ... What is Zs - kzhead.info/sun/e6iqcs-Hr4OAiq8/bejne.html What is R1+R2 - kzhead.info/sun/e9p9pbqEe6qsm6s/bejne.html Zs Where do the numbers come from - kzhead.info/sun/fM6peq9pnHyCra8/bejne.html
Do the 2 Ze tests apply to TT system? Thanks.
The figures for TN systems do not apply to TT systems because it is a soil earth path and not copper. You should still check Ze and Zs to confirm that is a return path but expect high readings, 80 ohms, 150 ohms etc. sometimes higher. We will be doing a video soon on TT systems. Thanks for watching.
@@learnelectrics4402 Thanks. I did Zs testing on TT before and the readings were very low; almost as good as TN. I suspect it is because of all the parallel paths from the water pipes, etc. Does the regs require that the parallel paths to be isolated (equipotential bonding be disconnected) before doing a Zs test for a TT system? Yes, I am eagerly waiting for your TT video. Many thanks.
Yes, test Ze on TT systems as you would a TN system and remove the main earth from the CU - with the main switch for the house turned off. pipework can affect readings and so can wet and dry weather. Lots more videos planned. Sorry for the late reply, your question only appeared here 5 minutes ago, lost in space somewhere. Take care. Dave.
@@learnelectrics4402 Thanks so much for your reply. Sorry if you don't mind, I was referring to Zs on TT. When you plan on releasing the video on TT, could you please clarify whether the 'correct' way to measure Zs on a TT system is to disconnect the main earth from CU. I'm not sure in practice whether this is being carried out. The multifunction tester manufacturer manuals does not seem to want to touch on whether to remove the main earth when doing a Zs test on TT. Thanks again.
I have given the method in the last reply, perhaps they have overlapped. Turn the CU off. REMOVE the earth conductor. Do a Ze test as if it was a TN system. Look in Guidance note 3 at section 2.6.14 Earth Electrode Testing - Test Method E3
On the top box of the SOTR form it asks for the ZDB. Some say ZDB is ZE. Others say ZDB is the global ZS of the installation. Which is correct??
A lot of folk ask this. There is only one ZE for an installation, at the incomer. So what do you do with the second CU if the circuit is extended. The incoming to the 2nd CU is a ZS from the 1st CU ( the cable from CU1 to CU2) It cant be a true ZE, but it is a ZE, a common cable, for the circuits on the second CU. So we call it ZDB on the forms meaning ZE at whichever DB we are at. Hope this helps. Perhaps I should do a mini video on it. Thanks for watching. Dave,
@@learnelectrics4402 that makes sense now thank you for explaining it 😊
Where does the letter 'Z' come from? How come that letter was assigned? Same with the 'R' in R1 and R2? Thanks.
It's just the way the electrical industry has grown up. We couldn't use I for Impedance because the letter I was already used by Monsieur Ampere for his "Intensity of Current". It was only called A for Amps after he died. If you get the chance, read up about electrical history, truly fascinating, and it started a few centuries earlier than most people think. Thanks for watching, Dave.
Imo this is gonna confuse learners - you say R1 + R2 is 'that part within the property including all the breakers, etc' - but R1 + R2 is just the measured continuity of line and cpc of an individual circuit, no?
The same thing. Thanks for the input. Dave.