Earth Loop Calculator 1.0.8
Calculate Ze, R1 + R2 and Zs, or estimate Ze from a measured supply-voltage drop under load.
1. Earthing arrangement and supply
2. Estimate Ze from voltage drop under load
Measure the supply voltage with the load disconnected, then measure it again with a known load operating. Use the actual load current where practical.
Ze ≈ (Uopen − Uload) ÷ Iload
This gives an approximate source impedance from the observed voltage change. It is most meaningful with a suitable predominantly resistive load, stable supply conditions and measurements made at the relevant supply point. It is not a substitute for the prescribed verification/testing method.
3. Circuit resistance and protection
Results
Zs = Ze + (R1 + R2)
| Earthing arrangement | — |
| Typical external Ze | — |
| Voltage-drop Ze estimate | — |
| Ze used | — |
| R1 + R2 | — |
| Zs | — |
| Supply fuse maximum Zs (5 s) | — |
| Circuit protective-device maximum Zs | — |
| 80% measured/test reference | — |
| Prospective earth fault current (U0 / Zs) | — |
| Margin to maximum permitted Zs | — |
| Assessment | — |
Calculation aid only. Confirm the applicable BS 7671 requirements, protective-device characteristics, installation conditions, DNO data and measured/test values for the actual installation.