RING CIRCUIT VOLTS DROP
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- čas přidán 30. 03. 2021
- The voltage that is lost in electrical cables is a product of the size of the cable, the current load and the length of the circuit.
Many electricians can calculate the voltage drop in radial circuits, but what about ring circuits.
Ring circuits are still very popular and not just in the UK.
How then, can we calculate the actual voltage drop for a Ring Final Socket Circuit to check that this is within the recommended maximum limit.
And what if we are designing a ring circuit, what size cable should we use and what is the maximum length that we can allow for our circuit.
There is a huge difference in permitted length in our favour, if we make the correct decisions and use the correct formula to make the calculations.
This is an easy to use formula and the method is very easy to understand but not so well known.
Knowing how to calculate the maximum length and actual voltage drop of a ring circuit will certainly be a bonus in your electrical career.
To view all our videos, click on the following link
/ @learnelectrics4402
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.
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Thank you for explaining this in easy understandable terms.
Glad it was helpful, thank you.
Thanks again, as an adult learner these detailed explanations are just what I need.
Much appreciated comments. Making sure the learner understands is so important in our trade. Thanks for viewing. Dave.
I have watched many videos on you tube regarding electrics, whilst there are some good explanatory channels, yours is by far the easiest to follow and absorb the information, its simply the best for learning.
Thanks for taking the time to post, it's been a massive help.
You are very welcome Adam. Thank you.
Passing a part p assessment was a breeze thanks to you. Thank you.
Fantastic news, really happy you passed. So glad we could help in a small way and do pass on our channel details to others to help them too. Electrics is a good trade, keep learning and you will never be out of work. Congratulations. Dave.
Fantastic explanation and presentation 👍
Glad you liked it Danny, thanks for watching.
These videos are superb. Keep up the good work.
Thank you for the great comments.
Yes, we intend to keep up the good work, spread the word. Dave.
Great video mty nice to refresh my grey cells
Glad you enjoyed it Andrew and yes, we all need to keep the grey cells topped up. Thanks for watching, Dave.
Thanks for posting,very helpful
Great to know you found it useful Alan. Thanks for watching. Dave.
Thank you very much, great video and as usual very clearly and easily explained. I find your videos so helpful, thanks for sharing your knowledge 😊
Thanks Darren, really appreciate your support. Dave.
Thanks for the help
Glad we could help. Thanks for viewing.
Well explained sir. 👍
Thank you Robert. happy we could help. Dave.
In the words of Alan Partridge..."lovely stuff" 👍
Thank you Mike. Great feedback, we are always glad that we can help. Dave.
It might help to explain that since there are two legs the length can be halved but also the current can be halved. this means the vd formula denominator is 2 x 2 x 1000 which is where the 4 comes from. It might make no difference but it helps some students.
Thanks for the comments Steven
Excellent content as always! I’m an apprentice electrician and today was the worst, stuck in a loft with rats and wasps etc, as a rule of thumb are most lofts in the UK like this, and do electricians spend a lot of time in lofts? Kind regards
It is sometimes the worst job in the world, but it never rains every day. There are good days, believe me. Most of us have had really bad days at some time, you've just got to get on with it.
Learn as much as you can and stick it out, electrics is a good trade, you will never be out of work and I've worked all around the world, literally. Learn a lot, be good at what you do and you can be your own boss one day, with your own apprentice to send in the loft.
Have fun and thanks for viewing, spread the word, the more that watch, the more videos we make. Dave.
So my question is when I'm designing a circuit and I've calculated my Zs to be 1.17 Ohms. When it is tested against using the MEASURED values of a 32a Type B Circuit breaker (Max Zs of 1.37 Ohms) it would be a fail? As 80% of 1.37 is 1.09 Ohms. So if we design to the TABULATED values there is a chance that during testing they would fail due to the 80% rule, but we don't account for it in the design phase?
I'm confused.
We do account for it in the design phase. At an average temperature of 20C we use 1.09 ohms for a B32. This means that as the temperature and resistance rise, the resistance will not exceed 1.37 ohms at the limiting temperature of 70C. Have another look at the video. Have a look at this video about Zs and the 80% rule. Dave.
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Hi, great vid thanks. Just a small thought, when calculating for ring circuit as you had mentioned in reality it is two cables in parallel, would the same be allowed or considered to be ok when measuring the VD or max length between say an MDB and an SMDB were the supply feeding the SMDB from the MDB is via 2 supply cables due to the load.
Have a look at appendix 10 of the Regs, page 497. Because of 3 phase reactive components of two cables taking the same physical route, current sharing should not be based on 50/50 each, but may be 70/30. In other words the voltage drop may be up to 50% higher than you would calculate for the single phase ring circuit. If you are borderline on cable sizes you may have to go up to the next size.
Thanks very helpfull
Please correct me and I apologize if I am wrong, In regards to ring circuits or radial regardless of both being susceptible to overload should we not have used "In" the protection rating instead of "Ib" the design current in the formula? similar to when we consider "Zs" in a circuit that is susceptible to overload when we consider and calculate all the rating factors to give us "It" the tabulated current. I do watch all your lectures and to date, they are the best explained on the net, Well done, and thank you
No, we use Ib, the design current. Take a 7kW shower, this is a single point circuit and it only uses 30 amps but has a 32 amp breaker. That could make an unnecessary size change in cable. We use Ib = 30 amps.
However, if you are talking about a socket circuit or a lighting circuit where you don't know what will be connected, we make Ib = In but still put Ib in the formula.
Hope this helps, good question.
Thanks appeciated.
Bang on. Thanks again for this wonderful lecture. Questions : the 98 metres, is it the length of the whole ring circuit? How do you measure voltage drop on a ring circuit?
Omar, thanks for the great feedback.
The 98 metres in our example is the whole length from leaving the circuit breaker on leg 1, all around the circuit and returning to the breaker on leg 2.
You cannot measure voltage drop with your meter unless you fully load the circuit to 32 amps, in this case, and measure at each point on the circuit. Far better to calculate as per the video. I would always prefer to calculate, it's safer, accurate, the accepted way and you can't get an electric shock off a pencil and calculator. Glad you enjoy the videos, lots more to come. Dave.
@@learnelectrics4402 Hi Dave, I work in a domestic environment and I have never thought of voltage drop in a ring circuit. My question is, when should I be concern my ring being to long ?
If you are designing your own circuits, at the design stage, but it is generally accepted that a ring circuit up to 100 metres is ok if the load is uniformly distributed. It is up to you to decide what uniformly means for your own circuit. Hope this helps. Dave.
Great video, I would like help to understand how I can satisfy the the formula Ib
A lot of folks wonder this, I will do a video on it. Basically a ring is two lengths of 2.5. Two times 2.5 is 5mm conductor. So now Ib≤In≤Iz is correct, if the ring doesn't break. Lots more videos on Ring circuits and testing on our website at LearnElectrics.com. Watch out for the video on your question in a couple of weeks. Dave.
Coudnt be more clear.. 🙏🙏🙏💥💥💥 Thank u so much.
Thank you for the great feedback. Dave.
Brilliant explanation, I understand the theory but, one question is, if I’m designing a new ring final circuit in say a new build property, how would we know how many amps will be drawn at any given socket outlet to aid us in working out average loads? Could we use 26amps as a good starting figure for all domestic rings?
Absolutely right. We will do a video on diversity soon, but in the mean time, diversity says that not all the sockets will be in use, not all the lights will be on at the same time and so on. The only circuit that might be heavily loaded is the kitchen ring at meal times so 26 amps could be a good figure to aim for. I know this gives a max length of 98/100 metres but 100 metres is a long, long way in the average 3 bed house, most times you are not going to get to 100 metres. Hope this helps and thanks a million for watching. Spread the word, there are lots more videos to come. Dave.
@@learnelectrics4402 thanks for your detailed response. I’m enjoying all your content so far, keep up the good work Dave👍👍
Great. always happy to help.
Would you consider running the City and Guilds 2396 course? or if not could you recommend me who does, your recommendation would be a great starting point.
See my other reply Angelo.
Hi Dave
Why is it a 32amp breaker for a ring circuit.
Why not 36 for instance or 40 amp.
Why was the 32amp standardised
See previous reply Andrew. Thanks for watching. Dave.
Would you consider running the City and Guilds 2396 course? or if not could you recommend me who does, your recommendation would be a great starting point.
I don't do classroom teaching now, just instructional videos.
We don't make any recommendations for courses or equipment, its not fair on the ones we don't recommend. There are lots of training centres on google search.
All I would say Angelo is choose your centre very carefully. Actually visit at least three centres before parting with any money. What facilities do they have, are the tutors actually trade electricians or have they just learnt it from books. Do they just teach electrics or do they do gas next week and plumbing last week. You want a tutor that has been on the tools. It is too late to find you have chosen the wrong training centre after you have parted with a few thousand pounds. Good luck and keep watching the videos. Dave.