Frequently Asked Questions about Small Circuit Breakers

1、 Basic understanding of products

Small circuit breakers, commonly known as air switches, are the core protective devices for terminal power distribution. Ordinary miniature circuit breakers (MCBs) have dual functions of overload protection and short circuit protection, which can effectively prevent lines and electrical equipment from being burned due to overload and short circuit, and avoid the risk of electrical fires; On the basis of the original function, the RCBO with leakage protection (RCBO) adds leakage and electric shock protection functions to ensure personal electrical safety. This product does not have lightning protection or high-voltage isolation functions and cannot be used in lightning protection scenarios.

The product is divided into three categories based on the instantaneous release curve, suitable for different electrical loads, and must not be mixed in civilian scenarios:

1. Type B: Instantaneous tripping current of 3~5In, suitable for low starting current loads such as precision electronic equipment and weak current equipment, rarely used in household scenarios;

2. Type C: Instantaneous tripping current of 5~10In, suitable for ordinary resistive and inductive loads, is a universal model for household lighting, sockets, air conditioning, kitchen and bathroom appliances, and is the preferred choice for civilian use;

3. D-type: instantaneous tripping current of 10~20In, suitable for motors, air compressors, high-power industrial starting loads, prohibited for use in home decoration scenarios.

1. 1P circuit breaker: only cuts off the live wire, with no protection for the neutral wire. It has a simple structure and low cost, and is only suitable for old-fashioned simple lighting circuits. There is a risk of electric shock during maintenance;

2. 1P+N circuit breaker: simultaneously connected to live and neutral wires, only the live wire has overload and short circuit protection functions, and the neutral wire has no protection. It is compact in size and suitable for small households to streamline distribution circuits;

3. 2P circuit breaker: The live and neutral wires are synchronously disconnected, and both poles have complete protection functions, with the highest safety. It is preferred for new home decoration, whole house circuits, and high-power electrical circuits

2、 Selection and matching specifications

All selection follows the core principle: the rated current of the circuit breaker shall not exceed the current carrying capacity of the supporting wire, and dangerous configurations with large switches and thin wires shall be avoided. The standard selection scheme for home decoration is as follows:
1. Lighting circuit: 10A, 16A;
2. Ordinary socket circuit: 20A;
3. 1.5 horsepower air conditioning circuit: 20A; 3 horsepower cabinet air conditioning circuit: 25A, 32A;
4. Kitchen high-power integrated circuit: 25A, 32A.

Civil copper wire adaptation specifications: 2.5mm ² copper wire can be adapted to a maximum of 25A circuit breakers, and 4mm ² copper wire can be adapted to a maximum of 32A circuit breakers. It is strictly prohibited to choose beyond the specifications.

This operation is strictly prohibited. The high temperature resistance and current carrying capacity of wires are fixed. If the current of the circuit breaker is simply increased, the circuit breaker will not be able to trip and protect in a timely manner when the line is overloaded and heats up. This will cause the insulation layer of the wire to age and melt, which can easily lead to electrical fires and pose significant safety hazards.

3、 Common troubleshooting and handling

   The cause of the fault is a short circuit in the circuit or equipment. Common scenarios include direct contact between the live wire and neutral wire, short circuit in the internal wiring of the socket, broken insulation layer of the wire, and short circuit caused by breakdown of internal components of the electrical equipment.

Troubleshooting: Disconnect all electrical equipment in the circuit and conduct a separate closing test. If it still trips, it is judged as a short circuit in the circuit and the wiring of the entire house circuit needs to be inspected; If the device can be closed normally and connected one by one, the corresponding device when tripped is the faulty device and needs to be repaired or replaced.

The core fault is electrical overload, where the total power and current of the circuit exceed the rated carrying range of the circuit breaker. This is often caused by multiple high-power electrical appliances being turned on simultaneously and the circuit load exceeding the limit. The fault feature is that the equipment can be closed normally after cooling and standing for a period of time, and then tripped again after running for a period of time. Solution: Reduce the simultaneous use of high-power equipment in the same circuit, or re optimize the distribution circuit and match the specifications of circuit breakers.

There are four common causes: 1 The service life of the circuit breaker is too long, and the internal release components are aging and the performance is ineffective; 2. Loose screws on the wiring terminals, poor contact and heating, triggering false protection; 3. Voltage fluctuations in the power grid and harmonic interference from electricity consumption lead to false tripping; 4. RCBO residual current circuit breaker triggers protection due to moisture in the circuit and slight electrical leakage. It is recommended to tighten the wiring terminals one by one, check the leakage situation of the equipment, and if the fault persists, replace the circuit breaker directly.。

1. Models with leakage protection (RCBO): Usually, the reset button does not pop out after the leakage protection is triggered. After pressing the panel reset button, it can be closed normally;

2. Model of ordinary circuit breaker (MCB): without reset structure, unable to close due to internal mechanical structure damage or jamming, without repair value, requiring direct replacement with a brand new circuit breaker.

Abnormal phenomena are classified as high-risk faults. Common reasons: loose wiring terminals, excessive contact resistance, and heating; Long term overload operation of the circuit; The selection of circuit breaker specifications is too small; Poor quality or aging of the product. In case of such a situation, immediately cut off the power and stop the machine for maintenance. Prolonged high temperatures can burn out equipment and cause line fires. It is prohibited to use the equipment with a problem

4、 Product usage and installation specifications

Qualified and legitimate small circuit breakers have electrical isolation functions, and 2P circuit breakers can be used as the main switch for the whole house in household scenarios. For industrial and high-capacity distribution scenarios, it is recommended to use dedicated isolation switches to enhance distribution safety.

1. MCB miniature circuit breaker: only has overload and short circuit protection, without leakage and electric shock protection functions, and cannot prevent personal electric shock and line leakage risks;
2. RCBO leakage protection circuit breaker: integrates triple protection of short circuit, overload, and leakage, with a leakage reset button on the panel. RCBO models must be selected for household sockets, kitchens, bathrooms, balconies, and other circuits that are prone to water and contact.

Only applicable to RCBO residual current circuit breakers: if the leakage indicator button on the panel pops up after tripping, it is judged as a leakage trip; If there is no indication button popping up, it is an overload or short circuit fault tripping, and corresponding targeted troubleshooting can be carried out.

5、 Maintenance replacement and safety warning

Under normal household conditions, the standard service life of the product is 8-10 years. If any of the following situations occur, immediately stop using and replace:
1. The closing is stuck, the operation is not smooth, and there is mechanical jamming;
2. Irregular, frequent, and inexplicable tripping;
3. The shell is yellow, deformed, and hot, with a burnt odor;
4. The wiring terminals oxidize and turn black, ignite when powered on, and discharge electric arcs.

Forcefully closing the switch is strictly prohibited. When the faults of short circuit and overload in the circuit are not eliminated, repeatedly forcibly closing the circuit will aggravate the burning of the circuit and equipment, generate electric arcs and open flames, expand the scope of the fault, and easily cause electrical fires and electric shock accidents. It is necessary to investigate and eliminate the fault before closing it again for use.

6、 Correction of common usage misconceptions

The larger the current of the circuit breaker, the safer it is. Correction: It is necessary to strictly match the cable diameter with the load. If the current is too high, it will lose its protective effect and cause a fire;

  1. Tripping indicates damage to the circuit breaker. Correction: Tripping is a protective action, and priority should be given to troubleshooting faults such as short circuits, overloads, and equipment leakage, rather than directly replacing the switch;

The lighting circuit does not require independent circuit breaker protection. Correction: All distribution circuits must be equipped with independent circuit breakers to avoid local faults affecting the electricity supply of the entire house;

D-type circuit breakers are more durable for household use. Correction: The D-type trip current is too high, which prevents timely tripping protection in case of household faults and fails to provide safety protection. It is prohibited to use it in home decoration.

Kind reminder: All electrical installation, maintenance, and replacement operations are recommended to be completed by professional electricians. Power off operations should be carried out to prevent live work and ensure electrical safety.

MCCB Common Problems & Solutions FAQ

Application：Export product manual, overseas after-sales service, customer technical consultation, foreign trade exhibition materials

Note：All solutions follow international electrical safety standards, suitable for thermal-magnetic and electronic MCCB with UVT, SHT, motor operator and residual current protection.

1. Operation & Closing Issues

•Reset the breaker firmly to the fully OFF position after overload/short circuit tripping, then close it again.
•Check under-voltage trip unit (UVT): MCCB cannot close if UVT is power-off, damaged or voltage mismatched.
•Ensure shunt trip unit (SHT) is not continuously energized, which will lock the closing mechanism.
•Check for foreign matter jamming, incorrect installation or busbar mechanical stress.
•Confirm cabinet door interlock is fully released.

•Match the operating voltage (AC220V/AC380V/DC24V) with motor operator rated voltage.
•Make sure the MCCB itself is not in tripped or UVT locked status.
•Check loose wiring, broken cables and blown fuses in control circuit.
•Inspect motor gear wear, stroke deviation and mechanical blockage.

2. Tripping Faults

•Instant trip: Check short circuit of rear-end cables or loads, power off and eliminate fault.
•Delay trip: Check load overload or three-phase unbalance, reduce load or replace matched MCCB.
•Electronic MCCB: Adjust overload setting current Ir to reasonable value.
•RCD type MCCB: Check cable insulation damage, moisture and earth leakage.

•Improve cabinet heat dissipation; high ambient temperature causes false thermal tripping.
•Tighten terminal screws; poor contact leads to heat-induced mis-tripping.
•Anti-harmonic interference for loads such as inverters and chargers.
•Solve hidden cable leakage and grid voltage fluctuation problems.

•Adjust short-circuit instantaneous setting current Im to match actual circuit parameters.
•Check rust, jamming and failure of electromagnetic/electronic trip mechanism.
•Replace aging MCCB with failed internal components.

•Reset overload current Ir for electronic MCCB; replace invalid thermal elements for thermal-magnetic MCCB.
•Adjust unbalanced three-phase load.
•Replace oversized MCCB with properly specified model.

3. Overheating & Temperature Rise Problems

•Tighten loose terminal wiring (the most common cause).
•Use cables with correct cross-sectional area matching MCCB rated current.
•Avoid long-term overload operation.
•Use copper-aluminum transition connectors to prevent corrosion and high resistance.
•Standardize wiring: one cable per terminal, fully insert wires into terminals.

4. Accessories Malfunction (UVT/SHT/Auxiliary Contact)

•Check if UVT coil voltage matches power supply voltage.
•Replace broken or burnt UVT coil.
•Clean and lubricate stuck UVT mechanical push rod.
Principle: UVT trips automatically when power off and prohibits closing without power.

•Check SHT voltage matching and wiring tightness.
•Important: SHT is only for short-time power-on; continuous power supply will burn the coil.
•Adjust mechanical gap or replace faulty shunt trip unit.

•Correct NO/NC wiring errors.
•Replace worn or oxidized auxiliary contacts.
•Ensure MCCB is fully closed or opened in place.

5. Selection & Installation Specification

•Thermal-magnetic MCCB: Low cost, fixed protection parameters (overload long delay + short circuit instantaneous), suitable for common lighting and power distribution circuits.
•Electronic MCCB: Adjustable precise parameters, 3/4-stage protection, support communication and leakage expansion, suitable for data center, photovoltaic, inverter and important precision equipment circuits.

•Vertical upright installation: Standard installation, full performance compliance, priority recommendation.
•Horizontal installation: Allowed for most models, slight thermal trip accuracy deviation, not recommended for precision protection circuits.
•Inverted installation: Prohibited without manufacturer’s special instruction, will reduce breaking capacity and cause protection failure.


•Install sealed distribution cabinets to improve protection level.
•Regularly clean dust to prevent inter-phase arcing and short circuit.
•Install anti-condensation devices in high-humidity environments.
•Use anti-corrosion MCCB for corrosive working conditions.

6. Core Parameter Explanation

•In: Frame rated current, basic specification of MCCB.
•Ir: Overload protection setting current, adjustable overload trip threshold.
•Im: Short circuit instantaneous setting current, fast trip threshold for short circuit fault.
•Icu: Ultimate short-circuit breaking capacity, MCCB may be damaged after breaking extreme fault current.
•Ics: Service short-circuit breaking capacity, MCCB can work normally after breaking fault current.

7. Quick Fault Judgment Table

 

Fault PhenomenonRoot CauseQuick Solution
Handle in middle position, cannot closeOverload/short circuit trip lockReset handle, troubleshoot circuit then close
Trip immediately after closingCircuit or load short circuitPower off, eliminate short circuit fault
Trip after running for a periodOverload / high temperature / loose terminalReduce load, tighten terminals, improve heat dissipation
Power available but cannot closeUVT lock / mechanical jam / interlock lockCheck power supply, clean mechanism, release interlock
Terminal overheating seriouslyLoose wiring / small wire gauge / overloadFasten wiring, replace cables, reduce load

1. All maintenance, wiring and debugging must be performed in power-off state.
2. Stop using MCCB immediately if there is refusal action, frequent mis-tripping, shell deformation or burning.
3. Do not modify internal structure, remove protective accessories or overload use MCCB.
4. Conduct regular inspection on wiring tightness, temperature rise, mechanical action and insulation condition.

Indicator Light Technical FAQ (Foreign Trade Version)

Scope of application: Industrial panel indicator lights, control cabinet signal lights, AD16 universal series indicator lights,

1. Why is the indicator light not turning on after power on?

•Wiring & loose contact: Check terminal wiring, avoid virtual connection, wire oxidation and loose screws. Measure actual voltage at the terminal.
•DC polarity reversal: DC indicator lights have positive and negative polarity. Reverse the two wires and test again.
•Internal component damage: LED chip or current-limiting resistor damaged by overvoltage, surge or long-term overload.
Troubleshooting steps: Verify voltage specification → Measure actual power supply → Adjust DC polarity → Replace a new light for test.

2. Why does the light glow dimly or flicker slightly when powered off?

•Induced voltage: Long cables or parallel wiring with power cables produce distributed capacitance and weak leakage current, causing dim glow of LED lights.
•Wrong wiring mode: The switch cuts off the neutral line instead of the live line, resulting in continuous live voltage on the light.
•Leakage current: Electronic relays, PLC modules or smart switches have tiny residual leakage current after turning off.

•Connect a bleeder resistor (100kΩ–220kΩ/2W) in parallel with the indicator light;
•Separate signal cables and power cables in different conduits;
•Adopt indicator lights with built-in RC absorption module.

3. Why does the indicator light flicker continuously during operation?

•Unstable power supply: Grid voltage fluctuation, large equipment startup/shutdown, or excessive ripple of DC switching power supply.
•Poor contact: Loose terminal wiring causes intermittent circuit connection.
•EMI interference: Interference from frequency converters, servo motors and high-frequency equipment.

Stabilize power voltage, tighten wiring, keep signal wires away from high-power interference sources, and add power filter if necessary.

4. Why does the light burn out quickly or overheat seriously?

•Overvoltage operation: Using low-voltage DC lights on high AC voltage is the main cause of burnout.
•Power surge & impulse: No surge protection; voltage impact from contactor switching and lightning induction.
•High ambient temperature: Installed inside closed cabinets or near heating components (transformers, contactors), poor heat dissipation accelerates aging and damage.
Suggestion: Use wide-voltage and high-temperature resistant indicator lights for enclosed and high-temperature working environments.

5. Are AC and DC indicator lights interchangeable?

•AC lights are built with step-down resistance or RC circuit;
•DC lights adopt current-limiting resistance design;
•Wrong connection will cause abnormal brightness or instant burnout.

AC/DC 24–220V wide voltage indicator lights support both AC and DC power, which are fully interchangeable.

6. Why do waterproof indicator lights fog or get water inside?

•Damaged or improperly installed sealing rubber rings;
•Burrs on mounting holes scratch the waterproof gasket;
•Condensation caused by severe temperature difference inside the cabinet.

Most panel lights are front waterproof only. For humid and temperature-variable environments, please use moisture-proof & condensation-resistant models.

7. How to solve indicator light mis-activation caused by EMI?
Strong electromagnetic interference from frequency converters and high-power equipment will cause abnormal light on.

•Separate signal cables from power cables, no bundled wiring;
•Use shielded wires for signal lines with single-end grounding;
•Install surge absorbers on the power supply side.

8. What affects the service life of LED indicator lights?

•Continuous overvoltage and frequent power surge impact;
•Long-term high-temperature working environment;
•High-frequency rapid on-off switching.

Avoid connecting large-capacity capacitors in parallel to prevent instantaneous impulse current damage.

Fast Fault Diagnosis Guide

1.Check wiring tightness and wire integrity.
2.Confirm light voltage type (AC/DC).
3.Measure actual terminal working voltage.
4.Adjust DC polarity and test.
5.Replace a new light to judge fault source (light or circuit).
6.Check induced voltage & wiring mode for dim glow issue.
7.Check surge & ambient temperature for frequent burnout.

Frequently Asked Questions about Small Circuit Breakers

1. Basic Performance

A: A push button switch is a manually operated electromechanical device used to control circuit ON and OFF. It is widely applied in industrial equipment, household appliances and control panels.

A: Momentary (spring return) works only when pressed and resets automatically after release. Latching type keeps ON/OFF status after each press without continuous force.

2. Electrical Specifications

A: Standard rating: 3A 250VAC / 6A 125VAC. Custom voltage and current specifications are available.

A: Yes. Please note that DC breaking capacity is lower than AC. Please use within the rated DC load.

A: Initial contact resistance ≤ 50mΩ; insulation resistance ≥ 100MΩ (100VDC test).

3. Service Life & Reliability

Q6: What is the mechanical and electrical lifespan?

A: Main causes include overload arc burning, contact oxidation, dust/moisture intrusion and overvoltage/overcurrent operation.

4. Protection & Environment

A: Standard IP40 and waterproof IP65 (with rubber cap) are optional.

A: Working temperature: -25℃ to +70℃.

5. Installation & Dimension

A: Common cutout sizes: Φ12mm, Φ16mm, Φ19mm, Φ22mm, Φ25mm, Φ30mm.

A: Suitable for panel thickness from 1mm to 6mm.

6. Illuminated Button

A: LED voltage: 6V, 12V, 24V, 110V, 220V; Colors: red, green, yellow, blue, white.

A: Caused by voltage mismatch, circuit leakage current or poor wiring contact.

7. Customization & Order Service

A: Yes, we support custom cap color, laser logo, terminal type and packaging.

A: Yes, free samples are available for quality confirmation, customers only need to bear the freight.

A: Standard order lead time is 7–15 working days.

DC / AC Contactors FAQs

1. What is the difference between AC contactor and DC contactor?

•Coil difference
AC contactor coil feeds alternating current; its core is equipped with short-circuit ring to eliminate vibration.
DC contactor coil uses direct current; no eddy current loss in iron core, no short-circuit ring required.
•Arc extinguishing
AC arcs naturally cross zero and are easier to extinguish.
DC arcs have no zero-cross point, requiring stronger arc chute structure.
•Structure & volume
Under equal power, DC contactors usually have larger volume.
•Application
AC contactor: control AC motors, lighting, AC loads.
DC contactor: battery systems, PV energy storage, DC motors, DC power distribution.

2. Can an AC contactor be used for DC load?

Not recommended for heavy DC loads.
When AC contactor switches DC, there is no current zero crossing, the electric arc lasts longer, contacts will ablate rapidly, leading to early failure.
Only allowed for small low-current DC loads under limited conditions; high-current DC must adopt dedicated DC contactor.

3. Can a DC contactor be used for AC load?

It works electrically in short-term tests, but not a preferred solution:
DC contactor contacts are designed for DC arc suppression. When switching AC, higher noise and unnecessary cost increase. It is better to select an AC contactor matching AC rated current.

4. Can a DC coil contactor work on AC power supply?

Generally prohibited.
DC coil has high DC resistance and low inductance. When connected to AC, impedance mismatch causes excessive coil current, coil overheating and burnout quickly.

5. Can an AC coil contactor work on DC power supply?

Most cases forbidden.
AC coil impedance relies on inductance. Powered by DC, inductance loses effect, huge DC current flows through the coil and burns it out instantly.

6. What does DC-1, AC-3 utilization category mean?

•AC-3: Switching AC squirrel-cage motors; make locked-rotor current, break rated operating current (most common for motor control).
•DC-1: Resistive DC loads (heaters, resistors).
•DC-3: DC shunt motors; make locked current, break rated operating current.

Note: The rated current marked under different utilization categories cannot be directly interchanged.

7. Why does the contactor produce arc when breaking DC circuit?

DC current has no natural zero-crossing point. After contacts separate, gas ionization forms continuous electric arc. Long-duration arc melts contact silver alloy, causing welding or contact failure.

8. What is contact welding?

Contacts cannot separate after carrying large current. Main causes:
•Excessive breaking current exceeding specification
•Severe arc ablation
•Undervoltage of control coil, insufficient contact pressure
•Frequent overload and short-circuit impact

9. How to select DC contactor for photovoltaic / energy storage system?

1.Confirm working voltage (12V/48V/150V/750V/1000V DC)
2.Continuous rated current
3.Breaking capacity (able to cut off maximum fault current)
4.Ambient temperature, installation altitude
5.Optional auxiliary contacts, coil voltage (12VDC / 24VDC / 48VDC etc.)

10. Coil voltage drop influence

If control voltage is lower than 85% rated voltage: insufficient electromagnetic suction, contacts vibrate, overheat and easily weld.
When voltage exceeds 110% rated value: coil overheating risk.

11. What are auxiliary contacts used for?

Auxiliary NO/NC contacts are for control loop interlock, status feedback, signal indication, interlocking between contactors.
Warning: Auxiliary contacts cannot carry main power load current.

12. Service life of contactors

•Mechanical life: millions of times (no load switching)
•Electrical life: far shorter, depends on load type, switching current and arc condition. DC load will greatly shorten electrical life compared with AC under equal current.

Switching Power Supply FAQs

1. What is a switching power supply?

Definition
A switching power supply (SMPS) converts input AC/DC voltage into stable DC output voltage by rapidly switching semiconductor power devices (MOSFET, IGBT). Compared with linear power supplies, it features high efficiency, small size and lightweight.

2. What are the main classifications of switching power supplies?

• By input type: AC-DC power supply, DC-DC converter
• By topology: Flyback, Forward, Boost, Buck, Buck-Boost, LLC, Half-bridge, Full-bridge
• By installation: Open frame, enclosed, DIN rail, plug-in adapter

3. Why does the switching power supply have output ripple & noise?

High-frequency switching action generates inherent ripple. Extra noise may be caused by insufficient output capacitance, poor PCB layout, ground loop interference or improper wiring.

4. What causes overheating of switching power supply?

• Load exceeds rated power / long-term operation under overload
• Poor ventilation, ambient temperature too high
• Blocked heat dissipation holes
• Input voltage out of specified range
• Internal component aging

5. Can the switching power supply run continuously at full load?

Most standard models support continuous full-load operation under specified ambient temperature and good heat dissipation. If ambient temperature rises, proper derating is required.

6. What is derating? Why is derating recommended?

Derating means using the power supply below its rated maximum load. It reduces component temperature rise, extends service life and improves reliability, especially in high-temperature or sealed installation environments.

7. The power supply works normally without load, but fails to start after connecting load

Common reasons:
1.Insufficient starting capability; heavy capacitive load causes startup failure
2.Output cable too long, large line voltage drop
3.Load short circuit or partial short circuit
Power supply current limit threshold set too low

8. What protection functions do standard switching power supplies usually have?

• Over Current Protection (OCP)
• Over Voltage Protection (OVP)
• Short Circuit Protection (SCP)
• Over Temperature Protection (OTP)
Some models support Under Voltage Protection (UVP)、Input Reverse Polarity Protection.

9. What is efficiency of switching power supply?

Efficiency = Output Power ÷ Input Power ×100%. High-efficiency SMPS reduces power loss and heat generation. Energy Level VI adapters and industrial power supplies usually achieve efficiency >85%.

10. Is it allowed to connect multiple switching power outputs in parallel?

Not recommended for ordinary power supplies without parallel function. Ordinary models lack current sharing circuit, which leads to uneven current distribution, overload damage. Only power supplies explicitly marked “parallel capable” can be paralleled.

11. What is isolation switching power supply?

Isolated SMPS uses transformer to electrically separate input side and output side. It enhances safety, suppresses interference and prevents electric shock risk, widely used in industrial control, medical equipment.

12. How to reduce electromagnetic interference (EMI) of SMPS?

• Add EMI filter at input terminal
• Optimize PCB layout, shorten high-frequency loops
• Use shielded wire, reasonable grounding
• Add absorption circuit for switching devices