K factor

[downundersparky]

Morning all, ant one care to explain/help with this ????

S= current sq x t

K sq

Current is it fault/design ???

Fault current sq ( 7137 x 2) X 2 secs

( 111x2 )

= 14274/222 = 64.29 mm

 

[jopo]

hello downunder,

AS/NZS 3000/2007 explains that formulas application at clause 5.3.3.1.2 and 5.3.3.1.3. to do with earth sizing. the clauses mentioned explain the application (I hope) in how or if to apply that calculation.

the formula actually is S= sqrt(I2t/K2). your calculation should be sqrt[(7137x7137x2secs)/(111*111)]=S = 90.91mm2

 

[Technician]

The I in the equation is the fault current that might be

from line to neutral or from line to earth. The k value

is from the regulations and is determined by the cable

material, the installation method, and the anticipated

rise in temperature. The time you have in your post is

2 seconds, is it? So you are stating that the protective

device is operating within a maximum of two seconds.

I assume that Jopo is quoting from an Australian code.