NEN 1010 §612.6
Fault-loop impedance
Lusimpedantie (Zs)
Also known as: lus, lusimpedantie, zs, loop-impedance, earth-loop-impedance
Loop impedance (Zs). Impedance of the fault loop phase → PE → source. Determines prospective short-circuit current Is and whether the overcurrent protection trips within the required time. Measure at each type test and after every change.
Practical example
Loop impedance (Zs): At a remote final circuit, Zs measures 1.8 Ω; with a 16 A Type B MCB, tripping time is excessive, requiring cable upsizing.
Common mistake
Loop impedance (Zs). Common mistake: Calculating Zs solely from cable length and cross-section without actual measurement—loose connections or corrosion in the path increase the actual impedance.
See also
Related terms
In-depth guides
- → Automatic disconnection of supply (AUV)
- → §612.6 (IEC 60364-6) Polarity verification at commissioning — why a swapped line and neutral conductor can be lethal without anything failing
- → §443 / IEC 61643-11 / IEC 61643-12 Energy coordination between Type 1 and Type 2 SPDs — the '10-metre rule' and decoupling impedance
- → §131 Protection Principles
- → §411.3.1 Earthing and earthing systems (TN, TT, IT)
- → §413.3 Electrical separation (§413.3) — an isolating transformer as a protective measure without earthing
- → §414 SELV, PELV & FELV — the extra-low-voltage measure
Beschikbaar in: English, Nederlands, Polski, Русский, Українська