Electrical Inspection, Testing and Certification Practice Exam

What does I pfc equal at the supply intake position?

1. Uo x Ze

2. Uo + Ze

3. Uo/ Ze

4. Uo - Ze

The correct answer is: Uo/ Ze

The correct choice indicates that the short-circuit current at the supply intake position, denoted as I pfc, is determined by the relationship of the voltage at the supply intake (Uo) and the earth fault loop impedance (Ze). This relationship can be expressed as I pfc = Uo / Ze. In this context, Uo represents the voltage at the supply intake, typically the nominal voltage, while Ze is the total earth fault loop impedance. The formula suggests that the short-circuit current increases as the supply voltage increases or decreases when the earth fault loop impedance increases. This is fundamental in assessing the potential short-circuit risk and ensuring that the electrical installation can safely handle fault conditions. By understanding that I pfc is influenced directly by both voltage and impedance, it's clear that this option correctly identifies how to calculate I pfc at the supply intake position, which is essential for proper electrical system analysis and safety protocols.