The differences and application scenarios of AC, A, F, and B type leakage switches

With the popularization of variable-frequency household appliances and LED lamps, the traditionally widely used AC type residual current circuit breaker has somewhat failed to keep up with the development of protection requirements. Then, should the existing installed AC type residual current circuit breakers be replaced? How to select the type of newly installed residual current circuit breakers?

1. What is a residual current circuit breaker (RCCB)? 

It is used to detect the difference in current between the phase line and the neutral line (residual current). When the leakage current exceeds the set threshold, it quickly cuts off the power supply. Personal safety: The typical sensitivity is 30 mA, which can trip when a person gets an electric shock. Fire protection: Sensitivities of 100 mA or 300 mA can suppress fires caused by small current leaks. Operating time (quoted from GB/T 16916.1): When the residual current = IΔn, the operating time ≤ 300 ms; when the residual current = 5IΔn, the operating time ≤ 40 ms.

2. What are the fundamental differences among AC, A, F, and B type leakage circuit breakers?

AC Type: Linear load, suitable for pure resistive/inductive loads (incandescent lamps, electric water heaters, etc.), only triggers for pure sine AC leakage action at 50/60 Hz. Any waveforms containing DC components or high-frequency components will not trigger.

Type A: Rectifier load, based on the AC type, can also recognize "sine AC + pulsating DC" waveforms (sawtooth current after half-wave or full-wave rectification). It still cannot detect smooth DC or kilohertz-level pulsating DC, commonly found in household appliances with rectifier bridges.

F Type: Single-phase variable frequency load, covers all the capabilities of Type A and extends to medium-high frequency pulsating DC (spectrum segments of single-phase variable frequency inverters and PFC circuits) ranging from 10 Hz to 1 kHz. However, it is not responsible for smooth DC. It is specifically designed for single-phase variable frequency household appliances.

Type B: Three-phase variable frequency load, extends beyond the F type: on one hand, it can trigger for up to 1 kHz of sine or pulsating DC leakage, and on the other hand, it can also detect 0 Hz of smooth DC.

3. For which scenarios is the AC type leakage circuit breaker suitable?

• Incandescent lamps, halogen lamps, traditional energy-saving lamps;
• Electric water heaters, resistance-type ovens, electric blankets and other purely resistive loads;
• Single-speed motors or household appliances without electronic speed control.

4. For which scenarios is the Type A leakage protection switch suitable?

• Electronic speed-adjusting/variable-frequency washing machines, variable-frequency refrigerators;
• Microwave ovens, electric rice cookers, computer and television power supplies;
• LED driver lamps and socket circuits with rectification.

5. For which scenarios is the F-type leakage circuit breaker suitable?

Household/compact commercial single-phase variable-frequency load

• Variable-frequency air conditioning outdoor unit, single-phase heat pump compressor
• Variable-frequency washing machine, dryer, dishwasher
• Single-phase variable-frequency water pump (swimming pool, floor heating circulation pump)
• Electronic speed control vacuum cleaner,power tools and other products

with PFC switching power supply

• High-power LED driving, power adapter, office printing equipment
• Small UPS, industrial control power supply, etc.

6. For which scenarios is the B-type leakage circuit breaker suitable?

• Split air conditioners / central air conditioners frequency converters;
• Photovoltaic inverters, energy storage inverters;
• DC and AC vehicle chargers, UPS, CNC machines.

7. What key parameters should be considered when making a selection?

• Rated Current (In): Select according to the maximum simultaneous load current multiplied by a margin of 1.2 to 1.3 (25 A/40 A/63 A/100 A, etc.).
• Rated Residual Operating Current (IΔn): Personal protection: 30 mA (10 mA for special areas);
• Fire protection: 100 mA or 300 mA (for the main total leakage protection).
• Pole Number: Single phase selects 1P+N, three phase selects 3P+N or 4P.

8. How to choose between 30mA, 100mA, and 500mA?

• Terminal circuits (bedroom, living room, children's room): 30 mA, for personal electric shock protection.
• Wet area terminals (kitchen, bathroom): 30 mA, in high humidity environments, personal protection is more necessary and it should not be relaxed to a higher current.
• Main distribution box total leakage protection: 100 mA - 300 mA, fire protection + selective coordination with the lower level. It is recommended to choose a delayed type (S type)
• High-power/industrial circuits: priority 300 mA. After calculation or measurement, if the leakage current is relatively large, 500 mA or above can be selected to reduce false tripping caused by leakage in long lines.

9. What are the precautions for installation and maintenance?

• Installation:

Install the leakage protection switch on the main incoming side of the distribution box, as close to the electricity meter as possible.

The phase wire and neutral wire must be routed through the zero-sequence transformer together. The neutral wire must not be mixed with other circuits or PE.

• Environment:

Keep away from high temperatures, high humidity, and corrosive gases. Regularly check for cleanliness. Especially for the distribution box in the kitchen, a sealed door type electrical box should be selected.

• Self-check:

Press the "T" key once a month;

The frequency can be increased during the rainy and humid seasons.

10. What are the differences between RCCB and RCBO?

• RCCB: Only provides leakage protection, while an MCB is required for overload/surge protection.
• RCBO: Combines leakage protection, overload protection, and short circuit protection in one unit, saving space but with a slightly higher price.

11. Do I need to replace the household AC-type leakage switch?

• Upgrade should be based on actual load: Safety hazard: The AC type will not trigger for pulsating/smoother DC leakage;
• Risk of false trip: DC bias may prevent the AC type from resetting or causing a false trip;
• Upgrade plan: Ordinary rectification, electronic appliances → Replace with A type; Those containing smoothed DC or high-frequency devices → Use directly with B type; The upper-level main leakage protection can still retain the AC type (or A type) to ensure "selective classification".
• New national standard charging piles have been equipped with 6mA DC monitoring since 2025, and no additional installation is required.