| Device terminology | Confirm whether “ELCB” means a residual-current device or an older voltage-operated earth-leakage breaker. | Current-operated RCDs are commonly called RCCBs; RCBOs combine residual-current and overcurrent protection. Voltage-operated ELCBs are an older technology. | The device type determines the protection method, wiring requirements, testing procedure, and applicable standard. |
| Protection function | Check whether protection against electric shock, earth leakage, overload, and short circuit is required. | RCCB/RCD: residual-current protection only. RCBO: residual-current plus overload and short-circuit protection. A separate overcurrent protective device is needed with an RCCB. | An RCD does not normally replace a fuse or miniature circuit breaker for overcurrent protection. |
| Residual operating current, IΔn | Select the rated residual operating current according to local electrical rules, circuit use, and risk assessment. | 10 mA: very high sensitivity for specific applications. 30 mA: widely used for additional personal protection. 100 mA or 300 mA: commonly used for equipment or fire-risk protection, subject to local requirements. | A lower IΔn provides greater sensitivity but can increase unwanted tripping from normal leakage currents. |
| RCD type | Match the RCD type to the current waveform produced by the connected loads. | Type AC: sinusoidal AC residual current. Type A: AC and pulsating DC residual current. Type F: selected single-phase frequency-controlled loads. Type B: AC, pulsating DC, and smooth DC residual current for suitable applications. | Modern electronic loads may produce pulsating or smooth DC components that are not suitable for a basic Type AC device. |
| Rated operational voltage, Ue | Verify the device voltage and frequency against the supply system. | Common low-voltage ratings include 230 V AC single-phase and 400 V AC three-phase systems at 50 or 60 Hz, depending on the installation. | Incorrect voltage or frequency selection can prevent proper operation and may create an unsafe installation. |
| Number of poles | Select poles according to the supply arrangement and neutral-switching requirements. | 2-pole devices are commonly used for single-phase circuits. 4-pole devices are commonly used for three-phase circuits with a neutral. Pole configurations must follow local wiring rules. | All live conductors required by the installation should pass through the sensing circuit; incorrect neutral routing can cause nuisance tripping or loss of protection. |
| Rated current, In | Choose a rated current equal to or greater than the expected continuous load, while coordinating it with the upstream overcurrent device and cable rating. | Common ratings include 25 A, 40 A, 63 A, 80 A, and 100 A, but the available range depends on the device design and installation standard. | The RCD rated current is not a substitute for cable and circuit-breaker coordination. |
| Trip-time category | Check whether standard, selective, or time-delayed operation is required. | Instantaneous devices are commonly used for final circuits. Selective or time-delayed devices may be used upstream to improve discrimination between devices. | Proper time coordination can prevent an upstream device from disconnecting an entire installation when only one downstream circuit has a fault. |
| Short-circuit coordination | Review the rated conditional short-circuit current or short-circuit rating and the required backup protective device. | The required value depends on the prospective fault current at the installation point and the applicable product standard. | An RCD must be installed within its specified short-circuit and backup-protection limits. |
| Applicable standard | Confirm that the product documentation identifies the relevant safety standard for its function. | IEC 61008-1: RCCBs without integral overcurrent protection. IEC 61009-1: RCBOs with integral overcurrent protection. National adoptions and local regulations may also apply. | A recognized standard provides requirements for construction, electrical performance, testing, and marking. |
| Nuisance-tripping control | Estimate the normal leakage current from filters, power supplies, motors, heating equipment, and long cable runs. | Avoid operating too close to the device trip threshold; the acceptable design margin should follow the applicable installation rules and engineering practice. | Accumulated leakage can cause unwanted disconnection even when there is no dangerous insulation fault. |
| Test facility and maintenance | Select a device with a clearly marked test button and establish a regular inspection and test schedule. | Pressing the test button should disconnect the device when the installation is energized; the exact testing interval is determined by local rules and the equipment instructions. | The test button checks the operating mechanism and part of the residual-current sensing circuit, but it does not replace professional electrical testing. |
| Installation environment | Check ambient temperature, humidity, dust, water exposure, enclosure rating, terminal size, and mounting arrangement. | Indoor distribution boards usually require a dry, suitable enclosure. Damp, dusty, outdoor, or corrosive locations require equipment and enclosures rated for those conditions. | Environmental conditions can affect insulation, mechanical operation, terminal reliability, and service life. |
| System compatibility | Confirm earthing arrangement, neutral connection, downstream circuit layout, and compatibility with generators, inverters, UPS systems, and electronic loads. | TT, TN, and IT systems can have different protection and disconnection requirements; some power-conversion equipment may require Type B or another specified RCD type. | The correct device depends on the complete electrical system, not only on the nominal current of the load. |