Based on these standards and regulations, the following main principles should be followed when selecting residual current devices (RCDs):
1. Purchase RCDs from manufacturers with production qualifications, ensuring the products have passed quality inspection.
2. Determine the RCD's power supply voltage, operating current, leakage current, and tripping time parameters based on the protection range, personal and equipment safety requirements, and environmental conditions.
3. When using RCDs for graded protection, the selectivity of the upstream and downstream switches should be ensured. Generally, the rated leakage current of the upstream RCD should not be less than the rated leakage current of the downstream RCD. This ensures sensitive protection of personal and equipment safety while avoiding cascading tripping and narrowing the scope of accident investigation.
4. Handheld power tools (excluding Class III), portable household appliances (excluding Class III), other portable electromechanical equipment, and electrical equipment with a high risk of electric shock must be equipped with RCDs.
5. Electrical equipment in construction sites and temporary wiring should be equipped with RCDs. This is explicitly required by the *Technical Specification for Temporary Electrical Safety at Construction Sites* (JGJ46-88).
6. Residual current devices (RCDs) must also be installed in socket circuits within government offices, schools, enterprises, and residential buildings, as well as in guest rooms of hotels, restaurants, and guesthouses.
7. Residual current devices must be used to protect power lines and equipment installed underwater, in humid, high-temperature, or otherwise highly conductive locations, such as workplaces in machining, metallurgy, textiles, electronics, and food processing industries, as well as boiler rooms, pump rooms, canteens, bathrooms, and hospitals.
8. Power distribution boxes with RCDs should be used for fixed-line electrical equipment and normal production operations. Temporarily used small electrical equipment should use RCD plugs (sockets) or socket boxes with RCDs.
9. When an RCD is used as supplementary protection to direct contact protection (but not as the sole direct contact protection), a high-sensitivity, fast-acting RCD should be selected.
10. For electrical equipment that cannot be powered off, such as power supplies for passageway lighting, emergency lighting, fire-fighting equipment, and burglar alarms in public places, alarm-type residual current devices should be selected to activate audible and visual alarm signals to notify management personnel to handle the fault in a timely manner.
