Leakage current and RCD selection calculator
An RCD trips on leakage current, but even healthy wiring and equipment has some natural leakage. To avoid nuisance tripping, the working leakage current should be no more than a third of the RCD's rating. The calculator estimates leakage current from the load and wiring length and compares it with the chosen rating.
Input data
Result
Fill in the fields — the verdict will appear here
Green — leakage current within ⅓ of the rating, no nuisance tripping expected. Red — close to the threshold: split the line across several RCDs, or use a higher rating (but don't raise the 30 mA one that protects people). Estimated from PUE guidance; a real measurement will show actual leakage.
How it's calculated
- Even healthy wiring has natural leakage: it's estimated as 0.4 mA per amp of load current plus 0.01 mA per meter of phase conductor.
- The working leakage current is compared with the RCD's rating: it must be no more than a third of it, or the device will start tripping for no reason.
- If it doesn't fit — split the line across several RCDs. Don't raise the 30 mA rating to fix this: it protects people, not the wiring.
Example: A 16 A line, 20 m long → calculated leakage is 0.4 · 16 + 0.01 · 20 = 6.6 mA. For a 30 mA RCD, up to 10 mA is allowed — there's margin.
Ileak = 0.4 mA·Iload + 0.01 mA·Lwire; working leakage current ≤ ⅓ of the RCD rating (PUE 7.1.83). A 30 mA rating protects people; 100/300 mA is for fire protection.
This is an estimate
Verify final values against current standards, the project design, and equipment nameplates.