Short Circuit Current Calculations

In this video we take a quick look at how to calculate the short circuit current on an electrical system using transformer information in a Radial distribution system.
When dealing with determining in a network system there are many more factors to take into consideration.
Edit; in the first example the 75000/120V should result in a secondary current of 625A not 312.5A. This would also, when used in the short circuit current formula, yield a short circuit current of 25000A. My bad.
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[@animal579]

i just spent 2 hours on an eaton video and learned alot at a system level, but still didn't learn how to do a SCCR basic calc. Now I got at least this part, thank you.

[@shrimp1948]

😂 I watched it to

[@brenden9755]

Super helpful gearing up for another take on my IP and no teacher could explain in the detail and tenacity that you have!

[@schulerruler]

Thanks for the encouragement my friend. I'm glad it's helped!

[@victorcolindres9273]

this is a great learning Mr Schuller ruler, I thank you for it, but data of single phase transformer calculation is wrong, the I sec is 625A not 312.5A , but again thanks.

[@jerrycamboim9216]

He divided by 240v instead of 120v. That's probably what happened

[@suvius4]

Thanks a lot dude! really helping me out for my IP prep!

[@ericstandefer9138]

Very cool, I have been wondering how this was calculated for a long time, thanks. (Subscribed).

[@schulerruler]

Thank you for the support!

[@yellow8954]

Again thank for this awesome content.

[@schulerruler]

Thank you for watching and supporting!

[@gunsparky]

Nice work. It's so hard to find watchable content on this topic.

[@masershasibhat]

Super talented. God bless you.

[@genespliced]

On your 75000va / 120v the result is actually 625A. Why do you get half (312.5A)? If you are using secondary L1 to L2 V as 240v, why not put 240v in the calculation for secondary current? Or use (x 2) in the denominator to indicate single line current for the 2 secondary Lines?

[@schulerruler]

Good catch. I honestly have no idea why I got 312.5. It absolutely should be 625A on this one. This would also make the short circuit current 25000A as well.

[@victorcolindres9273]

Thank youh so much Schuller , I am pretty sure we really appreciate these very important and refreshing knowledge in electrical. Thank you Vic

[@ajdsparky]

Thanks for clearing this up. However wouldn’t the short circuit be 2,500,000? 25,000 is 625/2.5%.? Thanks again. Just making sure I understand.

[@skinnymouse1410]

@@ajdsparky Ishort CCT = Isec x 100 / %Iz = 625A x 100 / 2.5 = 62500A / 2.5 = 25000Amps

[@jacobburesh8522]

great video! good to go back and watch these vids to reinforce what im learning in mach & xfmrs

[@schulerruler]

Happy they are helping!

[@ErkadalaMP]

It's easy to understand. Thanks a lot!

[@schulerruler]

Thanks for watching!

[@rajindermultani9972]

Hi I am confused about 75000va Devided by 120 volt .I get 625amp.how you get 312.5 amp.

[@dhrupadsaha4171]

Great teaching sir 🙏❤❤🇮🇳

[@schulerruler]

Thanks for the support!

[@manafkhalifeh6068]

great Explanations thank you !

[@johnhenry4113]

Hello, thank you for the video. Can you please do a s.c calculation for a final sub circuit further downstream in the electrical network. Say a lighting circuit 35 meters away from the transformer? Thanks again.

[@malcolmsg7442]

Thank you

[@gabopani]

can you explain this exercise ? A 100 kVA, 2400/240 V, single-phase step-down transformer has a 5% impedance rating. What is the minimum interrupting capacity rating for an overcurrent device that is protecting the secondary conductors of the transformer?

[@schulerruler]

100000va ÷ 240V will give you your secondary rated current (root 3 not needed as it's single phase). This can be used to determine the short circuit current using the same method in the video. Secondary current x 100 ÷ 5 will be the short CCT current. This is used to select the IR rating which must not be less than the short CCT current. Hope this helps!

[@sohailjanjua123]

Hi, I like your lecture. Thanks

[@JoseTorres-tw6xi]

what whiteboard program did you use in your presentation ? it looks similar to the Windows whiteboard , however the one one you used looks to have more features.

[@skinnymouse1410]

Which secondary voltage do you use to perform the short circuit calculation on a 3PH xfmr w/ 460/277 primary 208/120 secondary?

[@schulerruler]

208v but remember the root 3 as well.

[@jasonh8542]

This is a question I should already know but I am done trying to remember why. So why does the O/C protection rating for a short circuit current need to have a higher amperage that the Short circuit fault? Is it because it needs to handle such a huge in-rush of current but the magnetic trip is strong enough?

[@schulerruler]

It will withstand the internal force generated by the release of short circuit energy, as long as the rated interrupting rating is higher than the calculated minimum value. Underating could result in critical failure or rupturing of oc devices meaning injury, etc.

[@CarlosTorres-vx5zu]

A PV module has a surface area of 0.75 square meters and the radiation striking the module is 1000 watts per square meter. What is the short circuit current at 0.75 square meters, if at 1 square meter, the short circuit current is 8.5 A? what the formula for this

[@expnnt_designteam9609]

How do you compute for the overall %IZ of the banked 3 single phase transformers for 3 phase use ?

[@driftx2]

I got info from the utility company and they gave me a max and min %X for the transformer. Which do I use? I assume the smaller one gives you a more conservative number?

[@schulerruler]

I would always go for the sheer option with the smaller number as yes, as you mentioned it would be more conservative.

[@pramodgavit7666]

Sir can you post vdo on short circuit calculation for hone of 4kw load with suply 229v

[@krishnasamykesavan4816]

Great video. Need to know Copper bus bar short circuit current rating formula..or my bus bar size is 15 X 5 mm. Total 75 sqmm copper busbar in DB. Voltage rating 3 phase 415 VAC. give me the answer. Thanks once again. If any one please answer it.

[@gusakpan9730]

How do you find the impedance percentage?

[@schulerruler]

Here is a link to my video detailing the test performed to obtain the percent impedance! kzbin.info/www/bejne/bZLOgWZ7jraVb9U

[@maurogonzalez5792]

🔥

[@inder8750]

hey i have a question thats asking for fault current is that the same formula and also it gives me two coltages for the primary and 2 for the secondary

[@schulerruler]

What are the secondary voltages given?

[@possibility28able]

What happens in the event that the breaker is underrated for the short circuit? I. E you have a 10kva rating or AIR and the available short circuit current is 15kva?

[@schulerruler]

There's a good chance that the amount of energy will destroy the overcurrent device violently causing potential injuries

[@possibility28able]

@@schulerruler Interesting. Thanks for the response!

[@jasonh8542]

@@schulerruler so that’s why the OC protection rating must be the Short Circuit rating or higher. But I assume just because the OC Protection is rated higher doesn’t mean it won’t trip because the SSC fault value is less. This has kind of messed with me.

[@schulerruler]

Always size the interrupting rating of the overcurrent to the short circuit current, or higher preferably. If not marked, assume 5kA for Breakers 100 A or less, and 250 V or less, and 10kA for Breakers larger than 100 A or greater than 250 V. All fuses if not marked, assume 10kA. (Check appendix B 14-012 for this info)

[@jasonh8542]

@@schulerruler seriously you are the man for taking the time to write to your subscribers. It’s very much appreciated.

[@gabopani]

I see now thx

[@danielcarpenter9299]

What exactly is E Line? Is that a shortcut on the calculator?

[@schulerruler]

E line would be source voltage AKA line voltage. The E is the symbol that represents Electromotive force.

[@sanjeevbhogal6818]

WHAT ABOUT SCARY AUTOTRANSFORMER?

[@maddog4437]

6:25 what was EL?

[@schulerruler]

That would be the rated E line voltage, which in this example was 600Vac.

[@allpurposeconstructionwiz]

What does "I z" mean ?

[@schulerruler]

When used as %IZ it is the amount of voltage applied to the primary, compared to rated primary voltage, that will cause RATED current to flow on the secondary of a transformer, when the secondary is short circuited. This is obtained by performing a short circuit test on a transformer (which I do have a video on) but is usually a number listed on the nameplate as well. I hope this helps.

[@Buck1954]

SOOOO, What is "EL"?

[@schulerruler]

If you're referring to the abbreviation used in the formula, that's the line voltage, which is measured line to line.