3 PHASE PFC - How to calculate 3 phase Prospective Fault Current

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How do we calculate three phase fault currents if our test meters will only test single phase values?
Why do we multiply the measured values by different numbers and what do the numbers and the actual tests tell us about the circuit?
Which numbers should be written on the electrical certificates?
This video looks at 3 phase prospective fault current tests, explains why the numbers are what they are and which calculation to use for which test.
After working through this short video, your understanding of these 3 phase tests will be much more enhanced, giving you much more confidence when carrying out this type of test.
This video is number 102 on our RU-vid channel
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 RU-vid 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.

Опубликовано:

4 дек 2021

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Комментарии : 45

@Dog-whisperer7494 2 года назад

Excellent video. Brings back happy memories of my time at Watford college. Theses videos are a fantastic way of refreshing your memory and skills .theses videos should count as CPDs towards your continued learning. David is a great tutor, very clear and easy to understand. 👍❤️

@learnelectrics4402 2 года назад

They do count towards your personal/professional development tally Sean. Any relevant learning is counted, even reading articles in trade magazines. Just keep a rough note of the hours and subjects.

@adamoakes3367 2 года назад

I really hope you keep posting on RU-vid as i find the topics and the way you clearly explain everything ti be so helpful. I have watched many videos relating to electrics but yours are by far the best, you even give handy tips like 35 ÷ buy the fuse gives the zs, not something college gas ever taught but still a very handy tip. Wish you all the best mate and hope you keep posting as i will be starting my 2391 course soon and do watch your videos as an addition to my coursework.

@learnelectrics4402 2 года назад

Thank you Adam, what a fantastic response, brilliant. That is exactly the right thing to do, use the videos to supplement your college work. Thanks for watching and of course, we will keep making these videos. Lots more to come. Good luck with your 2391. Dave.

@joannamaciejewska869 9 месяцев назад

Again, so grateful for these videos. Thank you for sharing the knowledge.

@learnelectrics4402 8 месяцев назад

My pleasure Joanna. Thanks for watching. Dave.

@Prince-ep8pv 2 года назад

Perfectly done. Thanks!

@learnelectrics4402 2 года назад

Great feedback, really appreciated. Dave.

@michaelviney3737 2 года назад

I might be wrong but I think our 230v single phase supply voltage value is an RMS value and not the peak. Your diagram shows the peak of the wave form as 230 v Sorry to be picky …I do like your vids which are clear and informative.

@learnelectrics4402 2 года назад

It does Michael, which is why it says on the drawing that these are RMS peaks. Our meters works in RMS so no point in confusing folk with two separate waveforms. Thanks for your reply and thanks for watching. Dave.

@gbelectricks 2 года назад

Thank you Dave 👏👏

@learnelectrics4402 2 года назад

My pleasure, thanks for supporting the channel. Dave.

@angelofranklin1 2 года назад

Good Vid, very well explained.

@learnelectrics4402 2 года назад

Thanks Angelo, much appreciated.

@razomar-cs7wv 4 месяца назад

Thanks very much, so help full.

@learnelectrics4402 4 месяца назад

Glad it helped and thanks for watching.

@gayathriellawala4323 Год назад

nicely explained.. Thanks

@learnelectrics4402 Год назад

Thank you, great feedback and thanks for watching.

@jeremiahwhite3340 6 месяцев назад

Good video very useful thank you 🙏

@learnelectrics4402 6 месяцев назад

Thanks for watching. Dave.

@azizurrahman6663 2 года назад

Excellent video

@learnelectrics4402 2 года назад

Thank you. Appreciated.

@robertgemmell1485 2 года назад

Good vid cheers.

@learnelectrics4402 2 года назад

Thanks Robert. Thanks for watching.

@krazylad84 2 года назад

ThAnks much appreciated

@learnelectrics4402 2 года назад

You're very welcome. Thanks for watching. Dave.

@tent7014 2 года назад

Clear and concise Video. Just a comment about this being a 'live test'. Do you mean that the 3 phase DB is still live and not isolated or do you mean that the 3 phase DB IS isolated and the 'live test' is by having the tester pass voltage (230-500v) through the circuits ?

@learnelectrics4402 2 года назад

The main switch, the point at which you are testing is live. Even if the main switch is off, there will still be voltage on one side of it. You need the power to the switch to do the test. Hope this helps. Dave.

@skyfsa 2 года назад

Thank you for taking the time to do one of a kind tutorial. Do you have guidance in solving another topic calculating Max Zs for 60947-2 MCCB's without manufactures information?

@learnelectrics4402 2 года назад

That's a good question. I don't but it is something of interest for the future. Have you googled it? Thanks for watching and thanks for asking the question. Dave.

@colint001 2 года назад

Great video as always, there is one area of 3 phase I always get wrong and that’s calculating 3 phase cable size based on the equipment rating. I always spec too large a cable. If you could do a video on that it would be fantastic.

@learnelectrics4402 2 года назад

That is on the list to be done Colin. Soon. Too large is safer, but obviously costs more money. I've lost work in the past where another sparky has undersized cables just to get the work. Six months later, I was back in the factory replacing them with the correct size.

@azizurrahman6663 2 года назад

Hi Dave can you do more video for 3 phase adiabatic calculation and Ib and It and Zs and grouping factor. Thank you so much for excellent video

@learnelectrics4402 2 года назад

Azizur, adiabatics is to do with the size of the earth. The rest, yes, we have a 3 phase cable size video planned. Thanks for watching. Dave.

@erfan_muhammad Год назад

This is awesome. Thanks for sharing. Why Z=0.3ohm . How to get the value?

@learnelectrics4402 Год назад

If its a calculated value it comes from ohms law - voltage divided by pfc = Z. For some examples I just use a figure that helps to explain. Hope this helps.

@erfan_muhammad Год назад

@@learnelectrics4402 thanks.. keep up the good work

@benjamindhari Год назад

Dont you have to times the resistances as well by 2?

@learnelectrics4402 Год назад

Benjamin, absolutely not. The resistance of the wire is not changing. Whatever the resistance is, it stays fixed. Its the change in single phase and three phase voltages that changes the current. Thanks for asking and thanks for watching. Dave.

@wencireone Год назад

I have a tester that can measure phase to phase, but often will record a value which is less than double of single phase. An NICEIC inspector claimed that the value recorded is not double of single phase so is incorrect, is he right or is the test value more accurate, otherwise this would make the test of phase to phase be redundant and a waste of my time

@learnelectrics4402 Год назад

Have another look at the video, it does make this point. Three phase is not double the voltage of single phase, just root3. Hope this helps, Dave.

@ridefast0 2 года назад

I remember as an EE student many years ago, calculating the prospective fault level for a 400kV system, 3-phase to ground fault. It came out at around 35,000 MVA. Stuck in my mind on account of being a big frightening number (and a challenge to CB designers).

@learnelectrics4402 2 года назад

Absolutely frightening at times. I can remember carrying metal toolboxes through a substation and being told to stay on the paving stones and you'll be ok. Don't step off whatever you do. Thanks for watching. Dave.