K Factor again !!!!!!

[downundersparky]

Ok fellas thanks for the replys before, but can you check/help with this.

t = Ksq X Ssq/Isq ?????

t = 111 X 111 X 300 X 300/7143 X 7143 = 21.80 sec

S = 300mm consumer mains

t = 111 X 111 X 50 X 50/5523 X 5523 = 1.08 sec

Is this correct or near ???? t = the time it will take before the cable melts under fault current ????.

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Thanks fellas

 

[Phoenix]

Can you start from the beginning? WHat is it you are trying to prove?

 

[downundersparky]

Sorry Iam yrying to work out K factor for a consumer mains & sub mains

CM 300mm

SM 50mm

K factor as per AS/NZ 3008 for 300mm V75 = 111

I have worked out ( with a little help )

S = Sqrt of Isq X T/Ksq

CM = 7143X7143X2/111X111 = 91mm

SM = 5523X5523X1/111X111 = 49.75 mm

Iam trying to work out how long a fault current will flow before it damages the cable.

 

[downundersparky]

No takers ????

 

[Zeespark]

Downunder, its 230am here local time in the UK

AndyGuinness

 

[jopo]

down under t = sq root of (K2*S2/I2)

there fore the answer to to the sqroot of (111*111*300*300/(7143*7143))that gives answer of 4.66 seconds. looks like to forgot to square root it.

the other scenario of yours "t = 111 X 111 X 50 X 50/5523 X 5523 = 1.08 sec"

my answer is sq root of (111*111*50*50/(5523*5523))that gives answer of 1 sec even.