Zdb - WHAT IS IT? - WHY DO WE HAVE Ze? - WHY USE Zs? - TESTING Zdb & RECORDING ON TEST CERTIFICATES

Рет қаралды 10,513

Жыл бұрын

In this LearnElectrics video we will look at the measurement of Zdb - this mystery symbol that pops up on the Schedule of Test Results.
A recent question asked us …
Why do some certificates ask for Ze and some ask for Zdb?
There must be a reason for this, but I can’t find out.
Is there a logical explanation and if so, what is it?
So let’s look at this in steps and show you where we use Ze, where we measure Zs and just where Zdb comes into all this.
They are all an Earth Fault Loop Impedance measurement, they all use the same settings on the test meter, but what we do with the results and what they mean, makes a big difference.
To view all our videos type in LearnElectrics all one word into the KZfaq search bar.
This is video No.190 on our KZfaq channel where we have videos on a wide range of electrical topics.

Пікірлер: 102

@mcgee2k2 Жыл бұрын

I have to comment after watching a few of these videos, you are a brilliant teacher; very well explained from start to finish on every video. thanks for taking the time to do these; you will help a lot of people

@learnelectrics4402 Жыл бұрын

Thanks for the positive comments. Thanks for watching and spread the word, if we can help others ... Dave.

@basejumper01 6 ай бұрын

i concur, hugely helpful for someone like myself relatively early on into their electrical career. Learn Electrics is easily in my top 3 electrical youtube channels, Ive learned so much here and these videos helped clear up uncertainties i had when studying my level 2, as well as the 18th edition im studying for now.

@mwbg 2 ай бұрын

The wealth of knowledge on KZfaq is crazy, thanks for taking the time to put this together so well!

@learnelectrics4402 2 ай бұрын

My pleasure and thanks for watching. Dave.

@user-qi8tv2sj4m 5 күн бұрын

Second time if watching. Just a great teacher. Thanks.

@learnelectrics4402 4 күн бұрын

Keep learning, that's the secret. A little every day.

@alancooper7018 Жыл бұрын

Once again a truly educational video. The best explanation of Zdb on the internet and I have seen a few!! Thanks .

@learnelectrics4402 Жыл бұрын

Glad you enjoyed it Alan and great comments, thanks. Dave.

@Lyseredman Жыл бұрын

Excellent educational video as always. Thank you for taking the time to produce these.

@learnelectrics4402 Жыл бұрын

Glad you like them Tony and glad they are useful. Dave.

@NickyLong89 Күн бұрын

Thanks for explaining! 👏 very helpful.

@juicespirit Жыл бұрын

Amazing. Finally kind of understand what was taught in class :)

@learnelectrics4402 Жыл бұрын

Great to know that it's helped. Thanks for watching, Dave.

@gbelectricks 5 ай бұрын

Great explanation as ever Dave, if we had say, a TT system with one consumer unit connected. The Ze would be measured with the earthing conductor removed from the MET and we could expect a reading of say 100Ohms. Then if we reconnected the earthing conductor back on the MET and tested a Zdb measurement to the MET with all the bonding and CPC’s connected. We could then have a very low Zdb reading, due to perhaps neighbouring properties being converted to PME and where the properties share a common extraneous water/ gaspipe. So I think of a Zdb reading as the “actual earth fault loop impedance”👍

@learnelectrics4402 5 ай бұрын

See Guidance Note 3 - earthing method number 3. Leave the earth conductor and earth rod connected to the MET and do the same loop impedance test that you do for TNS or TNCS. Hope this helps. Dave.

@hussmortada Жыл бұрын

I love it! Very helpful and easy to follow as always. Cheers Dave

@learnelectrics4402 Жыл бұрын

Thank you Hussein, comments appreciated, Dave.

@hixlax5764 Ай бұрын

You Sir are very knowledgeable and the way you teach isbrilliant, i leant a lot from you and still learning, you will help a lot of people. thank you

@learnelectrics4402 2 күн бұрын

Always keep learning. A little everyday is the way to do it. Stick with it, it's a great trade. Dave.

@three-phase562 Жыл бұрын

Explained very well with clear diagrams. Thanks!

@learnelectrics4402 Жыл бұрын

Glad it was helpful and thanks for supporting the channel.

@hogg8888 11 ай бұрын

your really helping to tidy the trade the up. thanks so much for uploading these videos

@learnelectrics4402 11 ай бұрын

Glad to help and thanks for watching, Great comments, appreciated, Dave.

@steveellis9288 Жыл бұрын

Appreciate your work - brilliantly done, you’re a brilliant educator.

@learnelectrics4402 Жыл бұрын

Thanks Steve, appreciate the comments. Dave.

@davidpatterson1574 Жыл бұрын

Thanks Dave-excellent explanation and graphics

@learnelectrics4402 Жыл бұрын

Thanks for watching David, and thank you for the comments.

@martinburgess2322 Жыл бұрын

Brilliant as always.cheers Dave 👌👍

@learnelectrics4402 Жыл бұрын

Thanks Martin, appreciated.

@SamJ26. Жыл бұрын

Excellent, thanks for sharing this information.

@learnelectrics4402 Жыл бұрын

My pleasure Saam, thanks for watching.

@SuperAdz87 8 ай бұрын

went through this at college last night and couldn't get my head round it. Excellent explanation, Thank you..

@learnelectrics4402 8 ай бұрын

Glad it helped, lots to watch and lots to come. Thanks for watching and do spread the word at college, others may need the help too. Dave.

@HatBoyHarvey Жыл бұрын

Spot on mate, brilliant explanation and diagrams of the relationship in practical terms of the Ze/Zdb conundrum and what is simple but often rather confusing :-)

@learnelectrics4402 Жыл бұрын

Thanks for the feedback, appreciated, and thank you for watching. Dave.

@FredtheDog... Жыл бұрын

excellent description thankyou

@learnelectrics4402 Жыл бұрын

Glad it was helpful and thanks for the support. Dave.

@danielteyehuago1633 Жыл бұрын

Wow! This is very informative, thanks for sharing it with us. It worth it...wtc

@learnelectrics4402 Жыл бұрын

Thank you Daniel.

@arkstudios1 Жыл бұрын

As always excellent.

@learnelectrics4402 Жыл бұрын

Thank you Mr B and thanks for watching. Dave.

@MizunoIronMan Жыл бұрын

Vindicated at last - long story !! Thanks for posting

@learnelectrics4402 Жыл бұрын

Glad it helped. Thanks for the comments and for watching. Dave.

@frankieobrien2667 Ай бұрын

Spot on this video 👍

@learnelectrics4402 Күн бұрын

Glad you think so, thank you.

@paulward143 5 ай бұрын

Really useful thankyou.

@learnelectrics4402 5 ай бұрын

Thank you, appreciated. Dave.

@ibrahimabdullah4430 Жыл бұрын

1st view,like & comment 😁 Not watched the vid yet, but I know its gonna be good - added to watch later 👊😎

@juicespirit Жыл бұрын

It's good :)

@learnelectrics4402 Жыл бұрын

Thanks Ibrahim, there are 200 videos for you to work your way through. Thanks for visiting. Dave.

@learnelectrics4402 Жыл бұрын

Thanks for the support AF . Appreciated.

@BAYUMBE Жыл бұрын

Hi Dave, thank you for this wonderful video but has raised a lot of questions in my mind. You said theoretically the Ze of the db1 is = to ze of the db2. But between CV1 and CV2, there is R1 + R2 and on db2 we have to take it into account (video 5:20"). so, the Zs becomes the Ze of the db2. Now here are my questions: * Does R1 + R2 affect the Zs (Ze) of the CU2? How about The PFCC? Let say Ze at CV1 is 0.7 ohms, what will be the acceptable Zs and PFC at CV2 if it is found to be 20 m away of CV1? What can you say about voltage drop beyond CV2 on the circuit? * If from CV2 you want to add a CV3 at 40 m, what will be the acceptable Zs and PFC at CV3? what will be the maximum Zdb as we have Zs of CV1 to Cv2 and Zs of CV2 to CV3? Should we consider power drop? * can we apply the same principle on 3 phase?

@learnelectrics4402 Жыл бұрын

Zs should not exceed the values in the tables for the circuit breaker in use. Have another look at the video, it's all explained. Try and think what it is you are testing, at what point in the circuit. When filling in CU1 paperwork, CU2 is a ZS. But for CU2 certificates, that same ZS is now called a ZDB for CU2 Thanks for watching, sometimes you have to replay the video and learn a little bit with each watching. It can be a tricky concept to grasp at first. Dave.

@brianhewitt8618 Жыл бұрын

Excellent 👍

@learnelectrics4402 Жыл бұрын

Many thanks Brian.

@linksone6287 Жыл бұрын

Thank you so much! Very educational as usual! Can you also let us know in the comments what is Classed as a high integrity CCU please.?

@learnelectrics4402 Жыл бұрын

Its a consumer unit with three neutral bars, one for RCBOs, one for RCD1 and one for RCD 2. Allows the customer the best options of protection and discretion as to which device fails and which circuits stay on during a fault. Hope this helps. Thanks for watching.

@linksone6287 Жыл бұрын

Absolutely; it helps a-lot! Thanks for your reply! It’s most appreciated!

@sn2319 11 ай бұрын

Very well explained about the differences between Ze, Zs, Zdb and R1+R2. I am a bit not sure why still you have Ze, at the Zs calculation on 2 Consumer Unit? Thanks

@learnelectrics4402 11 ай бұрын

The second consumer unit has a common point for all the circuits that come off it, a common impedance (resistance) and we need to add this on to the R1+R2 readings. Have another look at the video, sometimes it helps to watch two or three times. Dave.

@digitaria Жыл бұрын

You missed something, Ze is measured different from Zs for Ze you remove the earth, for Zs you leave it in. In a lot of cases I have cone across the Zs value is lower than Ze due to parallel paths lowering the resistance. Another great video anyway, please keep up the great work.

@learnelectrics4402 Жыл бұрын

Thanks for the contribution, yes, sometimes that happens. Thanks for watching, Dave.

@AngelaPeters-fy1tc Жыл бұрын

Hi Dave so just to get this straight zdb is the same as ze at the initial consumer unit but at the subsequent consumer units after that its only zdb and not ze and is that because ze is only the external impedance and because theres a cable linking these consumer units then that is outside the external ze or impedance and is now on the consumer side and we have to measure the r1 and r2 values of that consumer unit to subsequent consumer units cable. Is this correct or maybe i should take your advice and watch the video again. Superb and educational video again by the way thankyou. Robert.

@learnelectrics4402 Жыл бұрын

You are right but please do watch the video again. Thanks for watching. Dave.

@ahmedalazazi2895 10 ай бұрын

Appreciate your great work I understood from you in case of additional CUs Zs equals Ze +Zdb +(R1+R2) Is correct?

@learnelectrics4402 10 ай бұрын

If you want Zs for the circuits at the 2nd board. It is Ze at the incomer. plus the R1+R2 to the 2nd board plus R1+R2 for the circuits on the second board. Hope this helps.

@ahmedalazazi2895 10 ай бұрын

@@learnelectrics4402 Many thanks to you

@nazk1901 11 ай бұрын

What if you build an Extention building to the rear of the property and you take 16mm swa from Henley block into new CU2 with a 60A fuse switch in between and your just doing and installation certificate for cu2 alone. Would u still need to do Ze at cu1? Would u need to check gas bonding in the old building?

@learnelectrics4402 11 ай бұрын

I would still do Ze for the installation and Zdb at the board that I work on. Hope this helps.

@zed.kelectrical8741 Жыл бұрын

Well.. nailed it again.. How the dickens do you make it seem so 'easy' ? 😃 Great lesson Dave.. You really should be invited to the 'Fat Sam' Electricians podcast..! I still can't believe these lessons are free..! but happy that they are.. Cheers.. 👍

@learnelectrics4402 Жыл бұрын

Great that help Zed, keep watching and lots more to come. All that I ask is that you tell others about the channel, that is reward enough. Cheers. Dave.

@shadeauto3373 Жыл бұрын

thank you for making these awesome and very clear educational videos, We all appreciate your help. 🤟

@learnelectrics4402 Жыл бұрын

Thanks for the great comment, appreciated. And thank you for watching. Dave.

@danielteyehuago1633 Жыл бұрын

Please i want to a you this question; what's the order in which you should arrange your circuit breaker in your consumer unit. should it be from the lowest breaker to the highest or highest breaker to the lowest and why... Thanks

@learnelectrics4402 Жыл бұрын

Daniel, usually put the highest next to the main switch/spd and work down. But as soon as you add to the installation it all goes out of the window.

@dennisfowler-dg5vf Жыл бұрын

hi dave another interesting vid...this kind of videos is wat i have searching the whole internet for and here it is...my other observation is... what if there is another fuse board some distance away....and is being fed from a hendly block....whould that measurement be a ZE or ZS

@paullyons4624 Жыл бұрын

I came to the comments to ask this question also. I suspect it’s not zdb as it won’t be supplied from an additional fuse. The whole point of loop impedance is to satisfy disconnection times. Would it be ze at db2?

@freezefoot Жыл бұрын

Good question

@learnelectrics4402 Жыл бұрын

If its the first board in the installation it will be a ZE and theoretically it should be the same as the "other" board as both are electrically the same point i.e. directly to the outside world. Hope this helps.

@learnelectrics4402 Жыл бұрын

See above, thanks for watching.

@learnelectrics4402 Жыл бұрын

Every question is a good question. Dave.

@ericthekingthekingtheking4842 8 ай бұрын

When a property or commercial floor or whatever is fed through a substation onto a rising busbar them where is the Ze taken from,

@learnelectrics4402 8 ай бұрын

Ze is usually taken where it comes into the property or building. The point at which it becomes the source for the circuits that it is supplying. Hope this helps. Dave.

@Apostolos-UK 7 ай бұрын

I dont understand why in a 3 phase DB we measure both the prospective earth fault current and the prospective short circuit current. My understanding is that the prospective short circuit current will always be bigger than the prospective earth fault current. So we double the value of the PSSC and we record this as prospective fault current. Am I wrong? Is there a case where the prospective earth fault current will be bigger than the prospective short circuit current? The PEFC is the only thing I do not understand why we measure. What am I missing?

@learnelectrics4402 7 ай бұрын

With PEFC we are testing along the Earth conductor. With PSCC we are not including the earth. Hope this helps. Dave.

@andygardner1523 Жыл бұрын

If the Zs of a circuit at CU2 or CU3 is higher than permitted values what should you do

@learnelectrics4402 Жыл бұрын

Good question. Take a look at the video on the link below. Thanks for watching. Dave. kzfaq.info/get/bejne/nLucdqeZ0cmolmg.html

@andygardner1523 Жыл бұрын

@@learnelectrics4402 Thanks for the reply . I would like to ask your thoughts on a discussion we had at work today . If you take a 63 amp circuit to the garage using a double pole switched fused isolator that is going to have for instance, sockets ,lights both internal and external and a future car charger and is 20 mtrs away from the house so an earth rod is put in and the earth in the 16mm 3 core SWA is isolated from the garage making it a TT system , having taken the supply from connector blocks before the consumer unit and and the incoming supply is a TN-C-S . When you come to test . Obviously at the house end you get a Ze reading at the switched fused isolator. At the garage CU on the test Sheet as that is a distribution circuit from the house would it be classed as Zs then on the form for the garage Zdb . Or would the Garage board be classed as Ze as it has a different earthing system to the incoming house supply

@detroutspinners9933 Жыл бұрын

So on the test paperwork you should record your Ze in the box marked Zs at DB?

@learnelectrics4402 Жыл бұрын

Record it where it says Zdb. Watch the video again, you will pick up where it explains this point. Dave.

@detroutspinners9933 Жыл бұрын

@@learnelectrics4402 thank you, these videos are really helpful for apprentices

@gino2465 Жыл бұрын

Would the zdb in real testing be higher ohms.

@learnelectrics4402 Жыл бұрын

If you mean will Zdb at CU2 be higher than Ze at CU1 then yes, because there is extra copper conductor involved. Thanks for watching. Dave.

@gino2465 Жыл бұрын

@@learnelectrics4402 Dave if this is you on your videos thank you. Your channel is just fantastic. Cheers

@livefree4661 Жыл бұрын

What happens when you hace a second remote board that had been converted to a TT system so the earth at source has not been migrated

@learnelectrics4402 Жыл бұрын

You would still call the second board Zs in relation to CU1 and then call it Zdb for the certificate for CU2. Hiope this helps and thanks for watching.

@livefree4661 Жыл бұрын

If im writing a cert for this remote board DB2 and the board suppling it DB1 is from a tncs then where do i record the readings for the rod on the TT ?