Max PSCC 1 phase and 3 Phase

[NZSPARK]

Hi all.


Prospective Short Circut Curret.

Now , if you measure the impedance on a installation P to N , and get a reading of 0.21 OHMS , the max current flow between these two points P and N will be 230/0.21 = 1095A.....1KA.


Now if you have 3 phases , and each are the same impedance P to N , the the max will be 1095A per phase , correct?


Now , if all 3 phases are shorted together , will this value still be the same , ie 1095 will flow from each phase , as the phases are 120 deg out of phase , will some of the current flowing from each phase , be actually some of the other , but the max will be 1095 through the MCB?


Say for instance a P to P fault with a 0.21 Impedance from each Phase to N.


Would 1095A flow from each phase , say in a RED to WHITE fault , 1095A would flow , BUT 1/2 the current that flowing in red is actullay some of whites , and in white its some of reds? ...

The same prinpical as normal operating current of a 3 phase motor?



Please Help!

Craig.

 

[GLENNSPARK]

it would be voltage measured/the impedence between phases....

 

[GLENNSPARK]

so...you can do:

Zpe...this is whats refered to as a Ze

Zpn...this is the short circuit impedence between each phase and neutral

Zpp...this is the short circuit between any two phases

 

[NZSPARK]

so...you can do:

Zpe...this is whats refered to as a Ze

Zpn...this is the short circuit impedence between each phase and neutral

Zpp...this is the short circuit between any two phases

Ok , but if the Impedance Phase to neutral is 0.21 , the phase to phase should be 0.42...../ almost doubble the Voltage , so the PSC will be roughly the same?

 

[GLENNSPARK]

PFC for 3 phase would be Zpn X square route 3

- - - Updated - - -

 

[Knobhead]

Just remember √3 = 1.732 in you’re calculations.

It’s not rocket science!

 

[guest119]

Or just double the sp&n reading.

 

[Deleted member 72666]

Both Tony and Boydy are correct!
The actual psc is 1095 x 1.732, but for the figure you enter on the cert is 1095 x 2.

 

[Knobhead]

So you are saying dumb it down for the uneducated?