Leakage protector selection - Solutions - Huaqiang Electronic Network

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1. What are the types of leakage protectors?

A: Leakage protectors come in various types, designed to meet different application needs. Based on their action mode, they can be divided into voltage-action and current-action types. Depending on the mechanism, they may be switch-type or relay-type. In terms of poles and lines, they include single-pole two-wire, two-pole, two-pole three-wire, and so on. Another classification is based on sensitivity and response time:

• High sensitivity: below 30 mA leakage current.
• Moderate sensitivity: between 30–1000 mA.
• Low sensitivity: above 1000 mA.

Based on response time, they are categorized as:

• Fast type: less than 0.1s.
• Delay type: between 0.1–2s.
• Inverse time type: the response time decreases as the leakage current increases. At rated current, it’s 0.2–1s; at 1.4 times, 0.1–0.5s; at 4.4 times, less than 0.05s.

2. What is the difference between electronic and electromagnetic leakage protectors?

Answer: Leakage protectors are classified into two main types based on tripping mechanisms: electronic and electromagnetic. The electromagnetic type uses an electromagnetic trip device as its core. When a leakage occurs, the mechanism triggers and cuts off power. Its advantages include strong resistance to interference and impact (like overcurrent and overvoltage), no need for an external power supply, and stable leakage characteristics even under zero voltage or phase failure. However, it has higher costs and more complex manufacturing processes.

The electronic type uses a transistor amplifier as the intermediate mechanism. When a leakage occurs, the signal is amplified and sent to a relay, which then controls the switch to disconnect power. This type offers high sensitivity (up to 5 mA), simple manufacturing, and lower cost. However, transistors are less durable against impacts and environmental changes, and they require an external DC power supply (usually over 10V), making them sensitive to voltage fluctuations. Also, if the main circuit loses phase, the protector may lose functionality.

3. What are the protection functions of a leakage circuit breaker?

Answer: A leakage circuit breaker primarily protects against electrical leakage. It should always be used with an overcurrent protection device. If fuses are used for short-circuit protection, their specifications must match the breaker’s capabilities. Modern integrated leakage circuit breakers combine leakage, short-circuit, overload, and undervoltage protection, simplifying wiring and reducing panel size.

When a trip occurs, it's important to identify the cause: a short-circuit trip requires checking for burnt contacts, while an overload trip means the thermal relay must cool down before re-closing. For a leakage fault, the issue must be resolved before re-closing. Never force close the breaker. The handle should be moved to the middle position when tripped, and pulled down before closing again. These devices are suitable for large-capacity appliances (over 4.5kW) that are not frequently operated.

4. How to choose the right leakage protector?

Answer: Selecting a leakage protector depends on its intended use and operating conditions. For personal shock prevention, use a high-sensitivity, fast-type model. For equipment grounding and shock prevention, choose a medium-sensitivity, fast-type. For fire prevention, go for medium-sensitivity, delay-type. For power supply mode, single-phase applications need single-pole two-wire or two-pole models, while three-phase systems require three-pole or four-pole models. Ensure the number of poles matches the line configuration, and never mix neutral (N) and protective earth (PE) wires.

5. According to the requirements of graded power distribution, how many settings should the electrical box have?

Answer: Construction sites typically follow a three-level distribution system: main distribution box, sub-distribution box, and switch box. Each level plays a specific role: the main box controls the whole system, the sub-box manages branches, and the switch box connects directly to the equipment. Each device must be controlled by its own switch box, and one box should not serve multiple machines. Avoid mixing power and lighting circuits in the same box. Electrical components must be compatible with the load, and boxes should be installed securely, away from moisture, heat, and vibration.

6. Why is hierarchical protection necessary?

A: Hierarchical protection ensures comprehensive safety by installing protectors at different levels—main trunk, branch lines, and end devices. This prevents unnecessary shutdowns during faults and allows for quicker fault identification. If a lower-level protector fails, the upper one can take over, minimizing risks. This approach enhances overall safety, reduces electric shocks, and ensures reliable power distribution across the system.