Earth loop impedance and prospective short circuit (PSC)

[Dave A]

Yes that im aware of. The measured value must not be more than the calculated value, as the calculated value is the upper limit threshold as you mentioned. My question now, when i calculate the value of the pscc, must i use the earth loop value calculated (1.90ohm) or the measured value (0.36ohm) to get the pscc? Because when i use the measured value of 0.36ohm, I get 633A which is closer to the pscc measurement of 674A.

You'd use the measured value. The objective of establishing the actual PSCC is to ensure the protection equipment is adequately rated to handle a short-circuit situation for that particular installation, so you need to be using the actual values of the environment.

As an aside, when you have a moment read Section 8.5 of SANS 10142-1 to get where I'm coming from on what the term "calculated PSCC" means.

[MullerR]

Now i'm getting closer to everything. Still a bit rusted, but between the books and guys like you who can answer me when I ask something, I feel more comfortable now.

Thank you Dave and Andy