RCD (Residual Current Device) Selection
Select RCD rated current, residual operating current, and type from load current, protection purpose, and leakage; check cable ampacity and normal leakage.
Key points
RCD (Residual Current Device) Selection: Select RCD rated current, residual operating current, and type from load current, protection purpose, and leakage; check cable ampacity and normal leakage. Formula: I_n ≥ K·I_load/temperature factor | I_Δn ≥ 3×normal leakage | personnel protection I_Δn = 30 mA. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. 30 mA RCDs protect people; 300 mA is often used for fire / overall leakage. Upstream and downstream devices should have different residual currents and a discrimination margin. An RCD protects against residual current (leakage) only, not overload or short circuit; socket circuits often use an RCBO (RCD + MCB).
Inputs
I_n ≥ K·I_load/temperature factor | I_Δn ≥ 3×normal leakage | personnel protection I_Δn = 30 mACalculation model (updates with parameters)
| Recommended RCD rating I_n | 50 A | 所needs ≥ 42.11 A（含Temperature降额） |
| Residual operating current I_Δn | 30 mA | 人身触电保护 |
| RCD type | A 型 | 含脉动直流，General |
| Normal leakage check | 通过 ✓ | I_Δn ≥ 3×1 mA |
| Cable ampacity check | 通过 ✓ | I_n 50 A ≤ I_z 63 A |
| Ambient-temperature derating factor | 95 % | 30°C 为 100%, by近似曲线 |
| Protection coordination | RCD + 断路器 / RCBO | RCD 不替代过载and短路保护；RCBO = RCD + 过流保护一体 |
Engineering notes
- 30 mA RCDs protect people; 300 mA is often used for fire / overall leakage. Upstream and downstream devices should have different residual currents and a discrimination margin.
- An RCD protects against residual current (leakage) only, not overload or short circuit; socket circuits often use an RCBO (RCD + MCB).
- VFDs, EV charging, and other loads with smooth DC components require Type B; a standard Type A may saturate and fail to trip.
FAQ
- What is RCD (Residual Current Device) Selection for?
- Select RCD rated current, residual operating current, and type from load current, protection purpose, and leakage; check cable ampacity and normal leakage.
- What is the formula for RCD (Residual Current Device) Selection?
- Core formula: I_n ≥ K·I_load/temperature factor | I_Δn ≥ 3×normal leakage | personnel protection I_Δn = 30 mA. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using RCD (Residual Current Device) Selection?
- 30 mA RCDs protect people; 300 mA is often used for fire / overall leakage. Upstream and downstream devices should have different residual currents and a discrimination margin. An RCD protects against residual current (leakage) only, not overload or short circuit; socket circuits often use an RCBO (RCD + MCB). VFDs, EV charging, and other loads with smooth DC components require Type B; a standard Type A may saturate and fail to trip.