TT SYSTEMS - WHY MUST THEY BE RCD PROTECTED
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- เผยแพร่เมื่อ 1 มิ.ย. 2024
- Why must a TT system have full RCD protection?
What happens during an earth fault?
Why can’t we use 1667 ohms for everything?
Can an RCD be fitted outside the consumer unit?
What about long meter tails?
These are just some of the questions we have been asked in relation to TT systems, and in this video we will answer these questions and show you some of the dangers of NOT having an RCD installed
This video is No.130 on our TH-cam 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 TH-cam search bar.
Always work safely, electricity can be dangerous. If you are unsure, stop and seek advice.
This video is provided for guidance only. Every electrical situation is different, please check and ensure that you are applying this learning information to your own individual circumstances correctly and safely. If in doubt, stop and seek competent advice.
I cannot praise this content enough! Short, clear and easy progression from one slide to the next and ensuring that the subject matter has been logically explained. Thank you.
Glad it was helpful and thanks for watching, appreciated.
Absolutely superb content. As a spark I do know this but you summarise and define the important points so well it’s a real pleasure to learn again. Thank you.
Thanks Mark, much appreciated. Dave.
As Sparks (my real name, really), I really appreciate the concise format and superb graphic aide.
I'm of the same opinion.
Most clear and interesting electric tutorial on TH-cam
Thanks for the feedback, appreciated. Lots more to come.
I love your content and really appreciate the effort that has gone into them. I regularly send my apprentices links to your videos too. You explain things so well.
Awesome, thank you, really appreciated. Keep spreading the word. Thank you. Dave.
Superbly explained with a no-nonsense approach, and the excellent graphics really help with the accompanying explanation. Viewing of these videos should be a must for all electrical apprentices.
Thanks Dave, great feedback. Yes, spread the word to the apprentice world. If we can help them to learn and enjoy the craft better then its a win-win situation. Thanks for watching. Dave.
As a townie, I rarely see TT systems, so these refresher courses are vital and fascinating.
Thanks Tugs. Some towns are TT systems. Parts of Shrewsbury where I used to live are still TT in the centre of town. Thanks for watching and for your support. Dave.
Dave I can not believe you on your teaching methods and explanation are so superb.
One of best channel for electrician as always.
Thank you.
Thank you, great feedback and thanks for watching, lots more to come. Dave.
Very clear explanation often not understood by many, it should be understood that the fault current is decided by the impedance of the fault circuit not by the rating of the RCD thus a considerable larger current can flow than the trip setting, that is why the trip time is as important as the rating and should always be within the spec or the device.
Thanks for the support, much appreciated, John.
RCD saves the the Lives, it also saves Installation!
Very true, thanks for watching.
@@learnelectrics4402
Would you refer me to a Scholarly article on line: when and where a Lightening Arrestor becomes mandatory for protection of a PV / Solar System?
Thanking in advance!
Boys and girls forget those other elec YT channels, Dave is the MAN, you want real answers come here. Missed some recent videos, sent a thumbs up to all those missed. Super content as always mate.
Thanks SteveO, great feedback. Thanks for watching, lots to come on Amendment 2 over the next few weeks. Dave.
Absolutely clear and professional explanations. Legend
Thank you Tedros, much appreciated feedback. Dave.
Thanks and Very best videos in electrical
Thanks for the feedback, appreciated.
Well put together and easy to under stand well done
Thanks Gary. Dave.
Absolutely Brilliant Work
Thanks for the support Imran, appreciated, Dave.
Best channel I've seen on YT for this subject. Clear, concise with no ambiguity and a massive help for all qualified electrical personnel and aspiring DIYers. Keep up the great work Dave. I just wanted to clarify one point. At 07:03 you state that "we could have a situation where 5A still flows into the appliance and 3.8 A of fault current as well". Excuse my ignorance (I'm a mechanical engineer!!) but I am trying to understand how this happens. Is this an instantaneous situation where the appliance is still running but in parallel develops an earth fault giving a total live current of 8.8A with the same coming out but split between neutral and earth?
That's correct Chris. Some current flows through the device and down the neutral, and more current flows along the earth because of the fault. But all of that current must come along the Line (Live). Think of a plumbing situation. 5 litres flows into the bathtub (the device) and we also have a leak of 3.8 litres. That means that 8.8 litres must flow through the supply pipe. Hope this helps and thanks for watching. Dave.
Brilliant. A subject which totally perplexed me. Thanks again for this well explained video
Thank you, great response and thanks for watching.
Great video, well explained. I like the use of diagrams, and the simple maths to show what is going on in which part of the installation, and why it matters.
👍
Thanks for watching Paul, really appreciated.
Excellent 👍
Thank you. Much appreciated. Dave.
Thank you for this video. I especially like that it was voiced by Vic Reeves - that added a really nice touch :)
Glad you liked it Alex. Yes, I have a rather recognisable voice. Thanks for watching, appreciated. Vic
So straight forward - Thank you. 👍
Glad it was of help and thanks for watching.
Excellent Velog on Essentiality of a Good Earthing / Grounding System Plus Installation of an reliable RCD in Every Domestic / Commercial / Industrial Electrical Wiring!
I'm grateful for Excellent Velog. Thank you very much!
Many thanks for the great support. Really appreciated, Dave.
@@learnelectrics4402
Thanking you again. I owe a lot to you. It's really a master piece. I got it downloaded for later reference.
Would you refer me to a Scholarly article on line: when and where a Lightening Arrestor becomes mandatory for protection of a PV / Solar System?
Another great explanation. nice one. 👍
Thanks for the great feedback and thanks for watching.
Thank you so much for your videos - superb content!
Glad you like them and thanks for watching. Dave.
Fantastic description
Thanks Andrew, appreciated, Dave.
Great video.
Glad you enjoyed it, thanks for the support.
Great information.
Glad it was helpful
Thanks for the video. Breaking the fault circuit down to its component parts and looking at the individual voltage drops certainly helped me understand TT earthing a little better. Looking at your channel I can't find a specific video on "Touch Voltage" and the implications that has on electrical calculations. Is that something you might consider?
Thanks, great feedback. Touch Voltage is the VOLTAGE that you experience if you TOUCH something metallic during a fault. I touched the water pipes and got a 100 volt shock. Touch voltage equals 100 volts. We want to keep it below 50 volts AC. Hope this helps Dave.
Excellent, as usual.
Thank you Gary. Dave.
Excellent explanation thank you sir
You are welcome Mohammed and thank you for watching. Dave.
Nicely explained
Thanks for the feedback, appreciated.
Another great video 👍
I appreciate your comments. Thank you Sal. Dave.
great video - can you explain the benfits of double pole RCBOs when they are used instead of split boards
Thanks Andrew. yes, RCBOs are coming up on a video session soon. Thanks for watching. Dave.
Well done
Appreciate your support. Dave.
Great content as usual Dave 👏 have you tried using the new condu-disks, they look so much better than a traditional rod. Have you done a video on testing a rod with the earth stake method?
Great info Mr B. Perhaps I should do a video on testing earth rods. Thanks for the nudge.
Outstanding content as always, I’m pretty much using you permanently as my CPD! Have you thought of offering some kind of CPD log or certificate if possible?
Thank you 👍
Great to hear that Craig. All learning helps. I used to hate it when my Engineering CPD was requested for inspection. Trying to remember what I had done over the last 12 months. I learnt in the end, write it down now. Thanks for watching, lots more to come. CPD log, no, not thought of it. You've got the grey matter thinking now. Dave.
Just a heads up though, around 9-10 min mark, the diagram shows the upfront RCD as a 30ma, although at the top it does say 100ma.
Well spotted Paul. I can remember changing this to 30mA. Guess I didn't press the save button. I'll change it right now. Thanks for the support. Dave.
Regarding all the changes in particular Residential Homes sites from 16th to 18th edition, Im struggling to find whether there should exist an RCD in the Site Distribution Boxes, on a site of 66 homes 7 Distribution boxes with a mixture of breaker sizes. However, when bad weather comes, some homes varies from 3 to 11 homes, depending on extremity of weather rain, lose power from DB's. Each home has its own Earth Road TT. The sensitivity is too high to allow the homes consumer boxes to act as designed. obviously the homes are certified at manufacturer EG OMAH Homes, Prestige Seekers Homes etc. any help in pointing out the required reading will be appreciated.
A lot depends on what loads are in use, their leakage etc. If you are having more problems in wet and bad weather, is there damp affecting some circuits, outside lights, sockets on damp walls etc. It doesn't take much for the leakages to add up. Can you get hold of the installation drawings from Prestige Homes or make contact with one of their technical people to tell you what was specified.
Brilliant video thanks , If you have full RCD protection on all circuits , does it still need a 100ma delayed RCD upstream as well? would it be a C3 or C2. And on a TT system do the circuits still have additional protection or is that not possible?
Thanks
An RCD only protects downstream of itself. So long meter tails may need protecting closer to the point where they enter the building. On a TT the RCD is giving the missing fault protection by the very same method that it gives additional protection. So in theory, your circuits don't have additional protection because there is no other protection to be additional to.
So do you need to rcd all circuits or main switch? Can you do either one?
All circuits need RCD protection. Some people will RCD protect the meter tails with a time delay RCD. Have another look at the video. Thanks for watching.
Great video, I have a question, if installing an up-front 100ma time delay RCD to further protect long tails and/or metal consumer units in a TT system, does the up-front RCD need to be in a metal enclosure ? as the latest consumer units ? or would an insulated enclosure be acceptable ? and maybe safer ?
Myself, I would put it in a metal enclosure, Keith. Hope this helps and thanks for watching. Dave.
@@learnelectrics4402 how about installing the RCD in a similar enclosure used for meter isolation switches ? which are mostly insulated e.g. Wylex ESI2S infact Wylex show this in one of their catalogs as a "made to order" item. There doesn't seem much difference between a 2 pole switch and an RCD apart from the coils and trigger mechanism, how prone are RCD's to catching fire ?
Very informative. If the tails are in swa cable would rcd protection still be necessary?
Its always a good idea to rcd protect them. Thanks for watching. Dave.
Dave, is the voltage
Yes, definitely less than 50 volts, it should be a lot less, just a couple of volts.
Below 3 volts.
Punch explanation. I am an electrical guy from India which follows TT earthing. Here people think fuse/mcb and earthing save them from leakage.
Keep watching, it all helps Kishore. I know what you mean about Indian Electrics, I used to work in India - Hyderabad. Dave.
@@learnelectrics4402 I am in Chennai.
Here earth pit resistance testing is not mandatory for domestic service, so people take advantage. Especially rented houses are not provided with proper earthing.
Electricians/contractors just drive a 3' long pipe irrespective of the soil condition.
You can find extension cords with 2 pin inlet and multiple 3 pin outlets (third earth socket dummy) being sold in reputed department stores!
When you say the voltage cannot go above 3 Volts are you speaking about RMS value or the peak voltage in the Sine Wave. Thanks
The device operates on current differences. Ohms Law tells us that voltage divided by resistance is current. If the resistance is low enough you will get enough current. Generally we talk about rms values as this is what our meters display.
With AC one always talks about RMS unless one specifically specifies peak.
What about is the Rcd is 32A 4 pole
Industrial and is connected to 30A 3 phase Switch
Thanks Emil, we will be doing a video on 3 phase RCDs very soon.
Can I ask if current is actually flowing through mass off the earth , how come we never randomly get shocks from the ground when people have faults? If you lived in a area where it was all TT systems for example
I think that is because the earth is such a massive object, and then some current flows this way and then some flows that way so it all cancels itself out. Science id scary at times. Thanks for watching. Dave.
If you were very close to a ground rod you would get shocked. The current dissipates to the earth and goes just a few meters.
@@okaro6595 step potential!
8:57 if the consumer unit is 50 m away, do we need to place a new earthing rod nearby the consumer unit?
You need the earth rod to be close to the consumer unit and the rest of the installation. Nothing wrong with having two earth rods.
Fantastic video as always Dave.
In thirty or so years I don’t think I have ever come across or seen a TT earthing system, I seen a good view TNS and I have lost count on how many TNC-S systems but can’t remember ever seeing a TT system. So I think this video is particularly interesting and informative to me.
👍👍❤️
It just depends where you live and work Sean. For many years I worked in rural Shropshire and mid Wales so lots of TT, even in some town centres. Dave.
@@learnelectrics4402 I come from London, now been living in Hertfordshire since 1986
Isn't the diagram of the external 100mA RCD wrong? There are 30mA written on both RCDs. The external should be 100mA and also the arrow on the top should be 100mA. Sorry if I'm wrong, please advise!
Probably me that forget to change the numbers when I copy and pasted. Thanks for pointing this out, I'll correct it.
So how will it not trip on an N - E fault on a S P rcbo and what dangerous things can happen with this fault
Its all about making an installation safe in the event of a fault. Thanks for watching.
Quick question anybody. Doing a ze on a TT system and the 100mA rcd keeps tripping. Got good Zs reading. Can anyone explain why it keeps tripping. Thanks.
If its happening during the test, you are testing at the wrong place. You should be testing upstream of the RCD. The RCD is seeing the test meter as a fault. Dave.
@@learnelectrics4402 Thanks for your reply Very helpful.
Hi Dave... Really enjoying your videos..An excellent learning tool and easy to understand... You're helping many people...
Just one question.. When you use the phrase "upstream of RCD" Do this mean, before RCD?
@@tonylynessable from the origin.
When Dave said I realized what I done. There was a lot going on with tails in and out of Henley blocks.
Would individual rcbos serve the same purpose, more expensive obviously though
Yes, RCBOs are great and the price is starting to drop. Todays video is about AFDDs and these can also be purchased as RCBO plus AFDD in one device. Pricey though.
Thanks for watching. Dave.
The part that says RCD breaks the circuit before reaching the voltage to touch voltage is tricky to imagine and understand. I mean thinking that operation of a mechanical element is faster than flow of electricity seems strange.
Absolutely it is difficult to imagine. I still can't believe that light can travel around the world seven times in a second.
7:45 I am still confused as to why the 6 amp breaker would not be sufficient? Please help me anyone! :(
Its a TT system so you can't get enough earth fault current through the soil. There is NO copper earth connection back to the transformer. Have another look at the video, it will help you to understand. Dave.
Also, have a look at this video, MCB - CIRCUIT BREAKER - HOW DOES IT WORK, click on the link below
th-cam.com/video/pBdMa9o6XJk/w-d-xo.html
This will explain why 8amps will not trip a 6A mcb, why you need an RCD
@@learnelectrics4402 I did just that and you have explained it very well. Thank you so much for replying good sir!
A breaker takes about 5 times the rated current to trip immediately. It may take 20% overload indefinitely and even 2x up to half a minute or so. A 6 A breaker might just trip at some time but not on the required time.
Can we use TT SYSTEM with only a RCD and without a grounding rod?
No. Checking you have an earth connection is part of the testing. Thanks for watching. Dave.
That by the definition would not be TT. It would rely on people acting as ground rods i.e. an energized equipment case could remain so until someone touches it. That actually is used in the United States to convert old installations without earth wires - but there the tripping current is 5 mA, not 30.
If you have a TT system, why cant you just P.M.E. it thus getting better earth readings?
Usually because the supply transformer is a long way away across the fields. You need the earth to be physically connected by copper between your house and the supply transformer.
@@learnelectrics4402 👍 thank you for such a swift reply.
Subscribed 👍.
P.s. is it advisable to p.m.e. And have an earth rod too? I have this in my own dwelling.
is M a motor or a meter
In the position shown there it is the electricity meter. Thanks for watching. Dave.
One could say this is a shocking video should you fail to heed its warnings..
Exactly Dave. Thanks for the support. Dave.