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

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 YouTube channel

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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.

[michaelviney]

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.

[tent]

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 ?

[Dog-whisperer]

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. 👍❤️

[colint]

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.

[erfan_muhammad]

This is awesome. Thanks for sharing.

Why Z=0.3ohm . How to get the value?

[benjamindhari]

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

[ridefast]

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).

[skyfsa]

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?

[adamoakes]

I really hope you keep posting on YouTube 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.

[wencireone]

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

[azizurrahman]

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

[joannamaciejewska]

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

[NaciMahmut-rfxf]

Great stuff. Well explained.
Do you teach?