3 PHASE LOST NEUTRAL - WHAT HAPPENS - WHY IS EQUIPMENT DAMAGED - A LOOK AT THE THREE PHASE WAVEFORMS
We’ve had questions asked recently about 3 phase installations and what happens if the neutral connection is lost. In particular, why is equipment damaged? Why is a 3 phase lost neutral serious?
As well as asking what happens if the neutral connection is lost, questions have asked how we can actually lose the neutral, why the equipment becomes damaged, and steps that we can take to prevent problems from happening in the first place.
In this video we will begin by looking at waveforms, both single phase and three phase and taking note of the differences. Then we will look at the effects of lost neutrals on the circuits and consider the reasons for the permanent damage that equipment can suffer from these very large over-voltages that can occur during these three phase problems.
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You are a gentleman and a scholar, sir. Keep educating! I'm sure many apprentices (and myself ha!) appreciate your lessons/explanations.
Thanks, will do. If we don't pass on our skills and knowledge who's going to fix my lights in the future. Thanks for watching. Dave.
I , unfortunately, learned it the hard way. Thank you for your lessons sir!
Sorry to hear that, put it down as a training session. Thanks for watching. Dave.
Hi, You have given a case. A 3 phase transformer present which drives 8 houses. Each phase has a fuse before reaching the house, inside house thorough MCBs home appliances are connected. Few appliances are running in few houses. Suddenly a bird hit one of the phase of transformer and it's link blown. In house 3, AC got blown which in running state. House 4 - 3 fans blown 2 running state 1 off state. Seen that neutral wires are blown and inside windings are blown. 1. Why not all devices blown in other houses? 2. in house 4, why all devices not impacted? 3. How does the devices affected which are in off state also ? 4. Good to hear the detailed analysis report explaining the cause and internal behaviour. 5. Tell the exact precautions which are needed to handle such situations in future. 6. How can we test the neutral and earthing fine at transformer and at home
This is why we install protective devices, to limit the damage and impact on other devices. Have a look at this video on fuses. kzhead.info/sun/hNmNk7yKpaedqYk/bejne.html
Only seen it once at a public swimming baths where there was a underground cable neutral failure many years ago. Lights glowing very bright and poping and a washing machine motor speed fluctuating wildly
Fantastic information. Really useful for our viewers to know. Appreciated and thanks. Dave.
Dave thank you very much. When you make explanations like these with diagrams it’s like I’ve just saved weeks if not months of time trying to work it out for myself or from other experienced electricians trying to explain what’s going on verbally.
Thank you for the great feedback. I try my best and its nice to know that its appreciated. Thanks again, Dave.
@@learnelectrics4402Have you made any video’s on reversed polarity Dave? Again an electrician was trying to explain to me how it works with the example of If the earth becomes live & so on. But I didn’t get it.
Great information. We have a few single phase VFD motor controllers in a sub panel that have different power requirements on each phase due to motor ratings so the same could happen here if neutral lost .
That's a good point Michael. Thanks for the info and thanks for watching. Dave.
Really helpful and well explained. Thanks for sharing.
Glad it was helpful, thank you.
Very very good. It has answered a lot of questions
Glad it helped, thanks for watching.
Great explanation, this was made easy to understand.
Thank you, and thanks for the feedback.
Thanks, always explained well.
You are welcome, appreciate your feedback.
Love ur channel well done mate
Much appreciated, thanks for watching.
Thanks for sharing it with us
My pleasure Daniel. Thank you.
Great information, excellent.
Thank you. and thanks for watching.
Great video, always the best, thanks mate
Thanks for watching. Lots more to come. Dave.
Thank you Dave.
My pleasure, hope you enjoyed it.
Again, well done.
Thank you, appreciated comments and thanks for watching. Dave.
Great explanation
Glad it was helpful and thanks for watching.
Another great informative video, please upload more 3 phase videos
More three phase! I'll put it on the list. Dave.
Well done, Dave anther well explained and important topic your effort and time most appreciated thank you.
Much appreciated feedback Anthony, and thanks for watching. Dave.
Great vid as always Dave! Thankfully never come across this personally. Did discover a over voltage on a certain warehouse once where for some reason the Transformer started out putting 300v per phase though. Amazingly only killed a few PCs.
Thanks for the feedback Andy. Yes, it doesn't take much to knock a PC over. Catch you soon.
Thank you for the information very helpful indeed. Please continue doing a great job. Karamat
Thank you Karamat, I will. Thanks for watching.
top job
exceptional
Great feedback. Thank you. Dave.
Very Good
Thanks. Appreciated comments.
We call this phenomenon as Floating Neutral. India.
Yes, that's another useful expression for it. Its a long time since I worked in India, Thanks for contributing. Dave.
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Useful
Glad you think so and thanks for watching.
when loosing N On supply side It’s best to switch off the main switch To Avoid damaging single phase Equipments- very helpful video as always thank you Dave
Thank you, really appreciated comments. Dave.
I found this very interesting, but it brings up a question? If the loss of a neutral on a three phase supply and is dangerous to the end user as well as damaging equipment, then why are new builds starting to have three phase supply’s as standard.? Surely this will put home owners at a higher risk of fire and injury or death. Great video as always 👍
Now that is an interesting question. Thanks for raising the subject. Dave.
Here in India we have 3 and 1/2 core service cables. 1/2 core is the neutral. Means neural size will be half that of phases. This is a cost cutting strategy. Electrically this is ok, but lacks mechanical strength.
Thanks Dave another interesting video in your usual straightforward style.
Something similar happened to me when I connected earth together with neutral, instead to the grounding pole clamp. Had to change the old three fase cable with just a neutral going in to the house, to a new one with added earthing. The main distribution board was outside, on the electric pole, the box was old and a seperate clamp to the ground was missing, so I connected earth to neutral. 2 mysterious weaks of dropping/jumping voltage and some damaged equipment. Thankfully the house didn't burn down and most of the equipment was repaired.
Lucky, glad you got it sorted. Thanks for the info, and thanks for watching. Dave.
Is there an Over Voltage Protection device at the Mains Distrtbution Board? What are they generally called?
There will always be an over-current device and sometimes a surge protection device (SPD) too. Take a look at thois video on SPDs, hopefully it helps. kzhead.info/sun/dqeTepR7h4GIZY0/bejne.html
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As always, thank you Brian. Your support is very welcome. Dave.
Dave, thanks for the insightful video. I have a question about the diagram at 07:37. What happens if N is connected to the local earth system (with an Earth Resistance below 4 ohms) and then downstream separated into N and PE at the distribution board level? This approach is quite common where I'm from. Does this practice mitigate overvoltage issues or exacerbate the risks in case of losing N upstream?
I've deliberately left earth of the drawings. In the UK we separate the earth and neutral at the intake position and do not run earth and neutral together in the installation. Without seeing how your wiring systems work, its difficult to say. Hope this helps.
@@learnelectrics4402 Dave, thank you for your response. It's interesting to learn about the UK's approach to separating earth and neutral at the intake position. In my country, we typically have (in aerial power line): L1, L2, L3, and PEN - that has the combined function of providing the neutral and protective earth. PEN is grounded at the intake position and at each 2 consecutive poles. At the customer's first distribution board, PEN is joined with the local earth system provided by the custemer (having no more than 4ohms) and then separated into PE and N.
If the natural is disconnected, will the circuit breaker in the distribution board activate and save the electrical appliances ?
The circuit just will not work. No current flow. The breaker will not operate unless there is a significant earth fault.
Thank you for the lesson. I have a question. My house is 3 phase but can be changed to single phase with change over switches, this is because of unstable electricity. Last night after a blackout the incoming voltage was 360v. I thought it was because the neutral was lost. I then changed everything over single phase (all load on 1 line and the “lost” neutral. The voltage went to 200v. Why is it that if the neutral was lost did the single phase work, did the 1 used phase use the other 2 non used phases as a neutral?
Without actually seeing this type of problem as it happens, its difficult to say. But thanks for watching and I hope all is ok now, Dave.
@@learnelectrics4402not sure as an electrical engineer you actually want to see the wiring in the house. Phases are changed over by wall sockets where all pins are live. You have a total of 9 sockets 3 phases with 3 lines per phase and a neutral line. Africa is scary
Would an AFDD provide protection against this fault as they have overvoltage protection? Thinking more in a single phase residential setting where the neutral fault is more likely to be with the DNO?
In my opinion, no. Not unless you have loose connections and arcing. With single phase, things will just stop. hope this helps. Dave.
Many thanks Dave
When we disconect a thre fase circuit first disonect the fases after neutral when we conect we connect first neutral
Always make sure that you have safely isolated the circuits. Thanks for the input, and thanks for watching. Dave.
How to calculate unbalance voltage for 3 phase each phase when lose neutral at unbalance load. Because that problem some time happen for people used over head 3 phase 4 wire power line.
As the video shows, the voltages can vary quite a lot. It depends just how unbalanced it is, what else is on the circuit etc. Thanks for watching. Dave.
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Great feedback, appreciated. Dave.
Overvoltage due to a lost neutral is bad news for any equipment. There is more bad news: if the voltage supplied is 230 V rms, then the voltage amplitude swings between -1.41*230=-325 V and +325V, which results in a (momentary) voltage of close to 600V.
Thanks for the comments. Dave.
Not so important, but no "Kirchoff", correctly it's Kirchhoff. Thanks the video! ✌️😉
It is, thanks for putting me right. You guys never let me get away with anything! Your feedback appreciated, thanks. Dave.
The electric company covered it? Here they would not, it would be up to your own insurance to cover it.
They did in my mother's case, and all her neighbours. Thanks for watching.
They did in my mother;s case. And all her neighbours.