TT SYSTEMS - RCDs Ze and Zs. How to make TT systems safe.
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- Опубликовано: 12 июн 2021
- TT systems have been around for many years and although TNS and latterly TNCS systems were introduced, there are still many installations around the country that still use TT Earthing Systems.
Perhaps the old adage still applies - if it isn’t broken, then don’t fix it. Indeed, there are occasions when TT Systems may still be installed.
We discuss what a TT system is, why we use RCDs or RCBOs and also discuss Ze and Zs.
We also take a look at R1+R2 in TT systems and how to check that the internal wiring and resistance readings are satisfactory in these installations.
This video is No.68 on our RUclips channel where we have videos on a wide range of electrical topics.
To see a full list of all our LearnElectrics videos, click on the link below.
/ @learnelectrics4402
You can also view all our videos by typing LearnElectrics all one word into the RUclips search bar.
Always work safely, electricity can be dangerous. If you are unsure, stop and seek advice.
SEE ALL VIDEOS - 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.
ruclips.net/channel/UCYaJQnpO4XAp0yCgqzMkmfA
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I have been confused too much by why use Fuses if RCD is there? Since fuses will only out if much larger current flow for a certain time but RCD is far or RBO is far quicker so can you please do a video why uses fuses then? Many will appriciate it , thank you.
Brilliant work. This is exectly how it should be thought in colleges. The method of explaining stuff is very elaborative, comprehensive and easy to understand.
Many thanks. 👍
Thanks Asad, great feedback, really appreciated. Dave.
Thank you TT systems and the max zs was something I wasn't sure on. This has helped massively . Keep up the great work.
Many struggle with TT systems. Once learnt, never forgotten. Lots more videos to come.
Great and clear explanation. I'm not a spark (an electrical engineer) with a TT system at home. This is the best distilled explanation I have seen in particular about the external RCD. Thanks
Super news Matt. If the videos help then that is their job done and thanks for watching. Dave.
With your help I managed to do 18th eddition. Passed Domestic Installer Niceic assessment. Recently Inspection and Testing. Thank you.
Really happy that I could help in a small way. You did all these things because you put the effort into proper preparation. Keep learning, its a good trade, its taken me around the world a few times. Take care and thanks. Dave.
Great video. We practice install front end RCD S type when there are gonna be submains.
Thanks for the input and comments, appreciated. A lot of folk do that too.
Thank you, this, by far is the best explaination of the ZS, Ze on TT I have seen. I have been trying to find a solution to the R1+R2 values as it was bugging me not knowing the Ze + R1 + R2 results.... Many thanks... I have been following you for a while and will continue to do so.... all the best..
Glad it helped Andy and thank you for your continuing support - really appreciated, Dave.
The best electrical instruction videos available!
Brilliant feedback, thanks. Dave.
Another great video. Credit to the industry. What I recommend to customers that have TT systems with high Ze/Zs reading is to get have it converted to a TNCS by the DNO. Western Power are the DNO in the area I live and do it quickly & cheaply for complete peace of mind in an absolute worst case scenario that the RCD doesn’t trip, I’ve only recently seen this in an 8 year old house. However, issue then with a TNCS system is for example having a hot tub installed is that some hot tub suppliers insist on the hot tub being installed on a TT system (incase of a PEN Fault) so an earth rod needs to be installed with no inter connectivity between the TNCS and TT system. In my opinion the crucial point to take from your video is the importance of RCDs on TT systems.
Thanks Paul, great info. Thank you for watching. Dave.
Thank you so much Dave. Hope these videos wont stop as they have been massive help !
Here's the deal. You keep spreading the word and I'll keep making videos.
Monday's video is about inrush currents and Type B C D breakers. I might squeeze in one about RCD earths over the weekend as well. It's good to have you around my friend.
Stay lucky and have a great weekend. Dave.
@@learnelectrics4402 thanks , looking forward to the new video.
I have already been recommending your videos to my level 3 friends.
keep on making great content thanks
Thank you. Appreciated.
You’re so resourceful… I am grateful for your help
Thank you Joel, much appreciated. Dave.
Great explanation and examples. Helped me alot!
👍
Excellent. Thanks for watching, lots more to come.
Your every video is to the point, best electrical channel, keep up the good work 👍 👏
Thank you Sal, appreciated and thanks for watching. Dave.
Brilliant video, very informative, thank you.
Glad it was helpful and thanks for watching.
Like always, a nice tutorial video. Will appreciate a similar video about IT arrangement in future.
Thank you Sajad, thanks for watching. Dave.
Great as always thank you.
Thank you Alan.
Video was a great help 👌
Thanks for the feedback and thanks for watching. Glad you found it useful. Dave.
Great work 👌👍
Thank you, appreciated. Great handle by the way.
THANK YOU!!!
Glad you liked it. Thanks for watching. Dave.
Excellent as usual!!
Rgds m.
Thank you Malachy. Thanks for the support. Dave.
thank you
You're welcome, thank you.
Really practically useful information. Thank you.
One thing I have found though. When performing my Ze test with megger mft 1552 it always trips the 100mA S type up front RCD. Any ideas for getting around that?
(I should say the s type is in the house and the cu is a sub main in an annex outside.)
Check the user instructions for the Megger. They may have a sequence of operations for that. It may be that the resistance of the cable to the sub-main is enough to attenuate the fault current enough to make the S type trip first as it is closest to the tester.
@@learnelectrics4402 thank you for the reply. That was my thinking too which is reassuring as I thought I was being really dumb! I appreciate your channel and time in replying.
Hi. i am doing the lottery tonight. Why? because i spent 3 hours trying to definitely research this subject yesterday. The amount of differing opinions on this actual subject especially on RUclips is outstanding. i watched one video where the presenter ( fat sparky ) waffled on about his " opinion". His opinion matters not. It is what the regs and the guidance says should be done. So serendipity. You publish this within 24 hours of me trying to fathom the current regs situation. So the way my luck is going its lottery tonight, collect money tomorrow, retire Thursday.
seriously though i would like to say that once again you have delivered a timely video on an esoteric subject. If there is a Patreon channel can you message me as i nearly contributed to another similar sounding name and i want to make sure that i support the correct channel. best regards
Thank you Caballo, really nice feedback and appreciated.
Glad I could help. Don't forget your lottery ticket.
Dave.
If there are no metallic services that require main bonding on a TT system, is supplementary bonding still required?
Hi. See above. Cheers.
For a radial socket circuit it occurred to me that R1/RN is similarly important for the overload condition, yet it doesn’t seem to get the same level of attention as R1/R2. Of course high R1/R2 is the shock risk , where high R1/RN is the fire risk.
Good observation Mike, few think about overload, volts drop etc.
@@learnelectrics4402 ??
Thanks Andy. Dave.
Hello Dave, please assist me with this technical issue. A building of six flats i carried out inspections on. What was the customer compliant. Whenever supply from transformer goes off customer lighting bulb still has slight glow, that is there's still voltage in it, same with some indoor sockets with LEDs on it. I discovered the building does not have an earth path for the building or earth wire in the consumer unit just line and neutral. Please can the absence of earth path cause this anomaly and how can this issue be resolved. Thank you very much
Obinna, if the earth to the building is missing this would be a supply company issue. If it's a TT system, then providing earth rods is the customers responsibility. Also check the polarity of the supply. Dave.
Earthing is not the issue. This is a 'symptom' that is commonly found with the more poor LED's, especially on 2 way lighting circuits. The symptom arises due to the very low load that the actual LED consumes. The symptom does not appear with say low voltage halogen, the reason why is down to the residual voltage is the secondary side of the transformer. The voltage will dissipate quickly through a higher wattage load. It takes somewhat longer for the residual voltage to dissipate in a LED circuit. Try changing the LED lights to a better make, JCC and Bell are very good makes I find. Alternatively you can connect a 300v (you will have to calculate the Impedance and wattage depending on installation) rated resistor between the Live and Neutral IN the light fitting, that will dissipate the voltage too. Regarding the LED on the socket circuit, the same issue, if the LED was replaced with the old Neon indicator, the voltage would dissipate a lot quicker and become unnoticeable.
So I don’t need to fit a 100ma RCD before my installation on a TT system? 30ma RCBO’S will suffice? Great video I know it mentions no rcd before the installation am I right in saying this?
With long meter tails you may need to protect them with 100mA RCD, some DNOs insist on it, others don't, but that will not protect persons, you need 30mA at the CU for that. Thanks for watching. Dave.
great videos many thanks can you do testing and inspection videos thanks again
They are on the list to be don - soon. Thanks for watching. Dave.
Hi ! So 100 ma rcd is not required for a meter tails?
100mA will protect devices and wiring. For persons and livestock it needs to be a 30mA RCD
Would it be sufficient to upgrade to an RCBO board ?
All RCBO boards are becoming more common. Yes, no probs.
I'm not a qualified electrician but I can say I frighten a lot of tradesmen since learning and applying the knowledge gained whilst following Learn Electrics... Fantastic confidence booster - If I may suggest something... It would be great to have test exercises to work through on the different subjects (unless it exists somewhere already). Thanks again.
Good idea, I can work on that.
If you want test questions on 18th Edition have a look at our 14 part 18th Edition Play list on this link...
ruclips.net/p/PLTVT88nFGKMy1sq4GLVX2SypMp4c9b-mf
Thanks for the support. Dave.
Enjoyed your video, however I have one comment. In your RCD section, you say that on removing the front end RCD and relying on the internal RCDs is a step backwards! I have to disagree. You highlighted the undesireable effect of having a front end RCD. I think you should clarify that the 7671 also states, in essence, that the removal of power on a circuit should not give rise to another danger. Cutting power from all circuits can give rise to over dangers such as tripping and falling. An analogy I have always used is: Imaging a winters evening and an elderly/infirm or visually impaired person is taking a bath/shower. Downstairs they have left a light on, the bulb blows. The RCD sees the surge as a fault and trips the power. We are left with a person, as above, having to negotiate getting out of a wet slippery bath, going downstairs and in a lot of cases, going to the outside CU to reset the breaker. This has happened. My belief is that RCBOs should be used on every circuit maintaining power to healthy circuits.
I would like to see RCBOs on every circuit, or with the suggestions from Amendment 2, combined RCBO and AFDD. Hopefully the costs will begin to fall soon.
Ze is measured between phase and the ground rod isn't it ?
That's right, the cable to the rod. You are testing that the earth cabke in the CU does actually give a good reading to the rod too.
Dave, will an RCD operate without an earth?
I've always installed them with an earth Mike. It gives them a reference point to the sensing coil.
@@learnelectrics4402 I wasn’t implying to install without an earth, but if the earth was not present for some reason, would the RCD still work? I had a customer with a spur that had no earth connection, my Kewtech meter would not test it.
That's right, its looking for an earth. The RCD needs a reference point to know.
RCCB works without earthing as per Kirchhoff's current law.
But RCD testers want earth.
ELCB's require earth for working.
Hope this helps.
@@30mAkills Thank you. Are you in the UK ?
If there are no metallic services that require main bonding on a TT system, is supplementary bonding still required?
Main Bonding and Supplementary Bonding are two totally separate requirements.
Not needing one does not mean that you don't need the other.
Have a look at our video - Exposed and Extraneous parts - on the link.
ruclips.net/video/MpiwTOSY1gw/видео.html
Thanks for asking.
@@learnelectrics4402 thanks
You are very welcome. Dave.
See IEC 61140:2016:
"5.3.3 Protective-equipotential-bonding
5.3.3 .1 General
Protective-equipotential-bonding is a provision whereby items are bonded together to avoid
hazardous touch voltages.
The protective-equipotential-bonding system shall consist of one or a suitable combination of
two or more of the elements below:
- protective-equipotential-bonding in equipment, see Clause 7;
- earthed or unearthed protective-equipotential-bonding in the installation;
- protective conductor (PE);
- PEN, PEL or PEM conductor;
- protective screen;
- earthed point of the source or artificial neutral point;
- earth electrode (including earth electrodes for potential grading);
- earthing conductor".
Protective earthing is a special case of protective-equipotential-bonding.