Wiring and Protection
Fault Loop Impedance Calculator
Fault Loop Impedance Calculator is meant for one defined wiring and protection case. Run a separate case when the equipment, period, or connection changes.
Model Fault Loop Impedance
Use one Fault Loop Impedance case at a time; save a new run when a condition changes.
The Fault Loop Impedance equation
Read the Fault Loop Impedance equation from the units on this page. A familiar symbol can shift meaning between DC, AC, energy, component, or billing work.
Before entering required trip current
On Fault Loop Impedance, confirm decimal placement and unit scale before using maximum loop impedance; small prefixes can move an electrical result by orders of magnitude.
- Nominal voltage. Example value: 230 V. Enter nominal voltage in V.
- Required trip current. Example value: 160 A. Enter required trip current in A.
When nominal voltage is uncertain, run a low and high case instead of hiding that uncertainty in one entry.
Use Current-Limiting Impedance after saving the Fault Loop Impedance case so the linked result does not overwrite these assumptions.
Detail checks for maximum loop impedance
Fault Loop Impedance requires installation context. Conductor material, insulation rating, bundling, raceway fill, and terminal temperature can change the acceptable value.
When maximum loop impedance becomes an input to another worksheet, copy the value only after the units and source condition have been verified.
Real-equipment notes for Fault Loop Impedance
A simple result is easiest to misuse when the input source is not written down. Label nominal voltage as measured, rated, assumed, or calculated before the answer leaves this page.
Keep Fault Loop Impedance with conductor material, insulation temperature, installation method, and protection type.
Quick check before using maximum loop impedance
- Keep the result note attached when copying the answer.
- Review zero or near-zero denominators before trusting a very large answer.
- Do not combine different equipment, time periods, or connection types in one run.
- Check whether the value is measured, rated, assumed, or calculated.
Audit trail for maximum loop impedance
Keep conductor material, insulation temperature, raceway method, ambient temperature, and protective device type with Fault Loop Impedance.
| Input set | Nominal voltage, and Required trip current |
|---|---|
| Result | Maximum loop impedance |
| Condition note | Verify disconnection requirements with the applicable protection standard. |
A separate Short-Circuit Current run is cleaner when that result becomes the real design question.
Help with maximum loop impedance
What should be recorded with the answer?
Save the Fault Loop Impedance inputs, unit basis, operating case, and result note so maximum loop impedance can be reproduced later.