Prospective short circuit current test

[kill the witch]

Hi all, fairly new to the forum so youll have to excuse my 'noobiness' as they say. I just watched this video of a guy showing how to carry out the above test.

Prospective short circuit current test - YouTube

This is taking place on a 3 phase supply. Does anyone know why he doubled the value given to equal 4.5Ka??

Any help much appreciated.

 

[topquark]

Should really be multiplied by 1.732 (square root of 3). He measured the potential current flow between neutral and each phase in turn, choosing the max. So between neutral and a phase that's what you could have flow. If however the fault was between two phases then you'd get roughly double the potential current flow. HTH.

 

[telectrix]

(square root of 2) 3,3,3,3,. go to the back of the class TQ.

 

[topquark]

(square root of 2) 3,3,3,3,. go to the back of the class TQ.

Arrggghhhh, beer and finger trouble, best edit that one

 

[brucelee]

the highest pfc will always be between the lines some test instruments cant carry out a test between the lines and can be dangerous
so for 3 phase we measure the highest line to neutral value Ie PSCC from eg
L1 - N = 500A
L2 - N = 515A
L3 - N = 505A

so L2 - N is the highest now multiply by 2 to get the estimated
3 phase pfc = 1030A or 1.03kA
this figure errs on the side of safety ie the worst case scenario
as topquark says a more accurate figure is 1.732 which is the sq rt of 3 not 2 which maybe a typo on his part

 

[topquark]

I think one of the reasons they say double it is that the voltage can vary a bit over time anyway, so taking a static reading can have a (small) degree of error as it may not be the max voltage that's (often) present. IE you may measure when it's around 232V and maybe it goes to a max of 239V.

 

[telectrix]

it was a typo or a beer related error, but i just couldn't resist it. LOL. :winkiss:

 

[topquark]

it was a typo or a beer related error, but i just couldn't resist it. LOL. :winkiss:

Nah, just dumb ignorance on my part hehehe