Preguntas Frecuentes

For bircuit breaker:

1. For a circuit breaker, its rated working voltage and rated working current shall not be lower than normal working voltage and normal working current or calculating current of corresponding circuit and device, respectively.
2. The setting current of the long time-delay tripper shall be equal to or greater than the calculating load current of the circuit, and can be determined as a value 1 to 1.1 times as large as the calculating load current, but shall not be greater than a value 0.8 to 1 times as large as long-term permissible current of line conductor.
3. The setting current of a transient or short time-delay tripper shall be greater than the peak current of the circuit; but for a distribution circuit breaker, it can be determined as per the principle of not lower than a value 1.35 times as large as the peak current; however, for a motor protection circuit, it can be determined as per the principle of not lower than a value 1.35 times as large as the starting current when the action time is longer than 0.2S; or not lower than a value 1.7 to 2 times as large as the starting current when the action time is shorter than 0.2S.
4. Rated short-circuit breaking and making capacity shall not be lower than the prospective short-circuit current of its installation position.

 Principles for type selection of contactor

1. Triple pole contactor is usually selected for a three-phase AC system, but to control neutral wire simultaneously, a four pole AC contactor shall be selected.
2. In a single phase AC system or DC system, it’s common that two poles or three poles are connected in parallel.
3. Generally, air-type electromagnetic contactor is selected, while explosion-proof type contactor or vacuum contactor shall be selected for flammable and combustible occasions.
4. Rated working voltage, current, making & breaking capacity, and withstand overload current shall be greater than parameters of the main circuit.
5. Coil voltage of a contactor shall be determined based upon the selected control-circuit voltage. Alternating current is usually adopted, but when the operations are frequent, direct current is usually selected.
6. Type, quantity and combination form of auxiliary contact are generally determined as per system requirements, but attention is also required to ensure that making and bearing capacity, and other rated parameters of auxiliary contact meet requirements for control loop.

Principles for type selection of thermal relay

1. Generally, the intermediate value of the setting current scope of a thermal relay is equivalent to or somewhat larger than the rated current of motor.
2.  In principle, the rated current of a thermal relay shall be selected as per the rated current of motor, but for a motor with poor overload capacity, the rated current of thermal relay is usually 60% to 80% of the rated current of motor and action features shall be checked.
3. If a motor needs relatively longer time to start up(usually over 5S), it’s not recommended to use a thermal relay, but the over-current relay shall be used for protection, instead.
4. For a motor that can be inversely operated and is frequently powered on-off, it’s not recommended to use a thermal relay for protection.
5. Usually, a thermal relay can be installed by several modes and user shall select one in a reasonable way.

Principles for type selection of voltage stabilizer

1. Pure resistive load(filament lamp, resistance wire, etc.): when selecting a voltage stabilizer, its capacity shall be greater than a value that is 1.1 to 1.3 times as large as the total load power.
2. Active, capacitive load(motor, fluorescent lamp, air-conditioner, etc.): when selecting a voltage stabilizer, its capacity shall be greater than a value that is 2.5 to 3 times as large as the total load power.

Principles for type selection of isolator and knife switch

1. An isolator’s rated insulation voltage and rated working voltage shall not be lower than that of the circuit, while the rated working current shall not be lower than the calculating current of the circuit.
2. If the bearing and making capacity is required, select an isolator of the rated bearing and making capacity accordingly, and consider its current features in making and breaking(for example, starting current and starting time).
3. It’s necessary to conduct a short-circuit performance checking for an isolator, so that the prospective current at its installation position is not greater than the rated short-time withstand current of the device(or rated limiting short-circuit current, if there is a short-circuit protector in the circuit).
4. For fuse combination unit, it’s necessary to consider the features of the fuse, as well.

Principles for type selection of transducer options

1. AC input reactor or DC reactor (for civil use) shall be selected for the following conditions:

    –    If not used for a power supply(central air-conditioner motor of a hotel) greater than 55KW and poor power grid or conditions with relative small capacity, it  may cause interference and excessively large deviation of three-phase current, and frequent transducer burnout.

   –     The distance between a motor and a transducer is greater than 100m.

2. Braking unit and braking resistor shall be selected for the following conditions

  –      The load is being limited.

  –       Rapid acceleration and deceleration frequently.

  –       Large inertia(a device that needs more than 1 minute for free stopping and for which constant-speed operation is smaller than accelerating current).

Principles for type selection of rated current of general fuse

1. For a fuse of protecting lighting or electrical heating appliance that has a relative stable load current, and a fuse for general control circuit, the rated current of its fuse link(In) is often determined by calculating current of the circuit.
2. For a fuse used to protect a motor, it’s necessary to consider the effects of the motor’s starting current as per a value that is several times as large as the motor’s starting current; generally, the rated current(Ife) of a fuse is 1.5 to 3.5 times that of the rated current(Ime) of the motor.
3. Cylindrical contact cap fuse(for example, RT28 series) is not suitable for the protection of capacitor box, so for capacitive protection, please select a square tube fuse(for example, RT36 series).
4. Options for fuse used together with other switching device.

•          All elements shall go with each other properly in protection features.
•          Time-Current features of thermal relay and fuse must meet the time delay features of the motor from zero-speed start-up to full-speed running.
•          In addition, a fuse must be able to protect the thermal relay from being damaged by a large current that is 8 times or above as large as the rated current.
•          The fuse shall protect the contactor as well, under a condition of short circuit.
•          When a circuit breaker is used together with a fuse, the fuse is mainly used for the breaking of a large short-circuit current.

How are residual current devices classified, according to action features when residual current is with direct current component?

1. As computer, electronic office device and household appliance are used widely, the direct current component is larger than ever increasingly in the circuit. Direct current component(if any) in a residual current may have an effect upon action features of the residual current devices, which can be classified as follows, according to working conditions when there is direct current component in residual current:
2. Type AC: refers to those residual current protection devices that can complete the tripping action, when residual simple sinusoidal alternating current is applied suddenly or increased slowly. They are used in common AC circuit.
3. Type A: those residual current protection devices that can complete the tripping action when either residual simple sinusoidal alternating current or residual pulsating direct current is applied suddenly or increased slowly. They are used in a circuit with multiple electronic devices, including household appliance, office appliance and computer. (Note: type A devices are available for NB1L and NL1 in Chint Group.)
4. Type B: similar to that of Type A; this type is mainly used for electrical devices that produce smooth direct current, for example, variable frequency, X-ray machine and UPS power supply. (Note: Type B devices are temporarily unavailable in Chint Group.)
5. Type S: this type is specially designed for a given residual current to reach a predetermined limiting non-actuating time. This type is mainly seen in higher level circuits to avoid override trip

What is the difference between NB1 and eB?

What are the accessories available for NA1-2000?

1. Auxiliary contact: it indicates information about making and breaking of a circuit breaker or controls the making and breaking capacity of a circuit. Generally, the factory default setting is a four-group changeover contact, but it is available to customize a five-group changeover contact, a three- normally-open and three-normally-closed contact, and a four- normally-open and four-normally-closed contact. For a circuit breaker with undervoltage time delay function, the default setting is usually a three-group changeover contact, but it’s also available to customize a four-group changeover contact, and a three- normally-open and three-normally-closed contact;
2. Undervoltage time delay release: when the power supply voltage is lowered to an action voltage, circuit breaker will be opened after the specified delay time, but if the power supply voltage may get back to 85% UE or above in 1/2 of the specified delay time, then circuit breaker will not be opened; there are three types of trippers for selection, namely, 1S, 3S and 5S, but they are not adjusted;
3. Phase barrier: used to enhance the phase to phase insulation capacity of a circuit breaker;
4. Breaking locking device: lock the partition position of drawer type circuit breaker;
5. Key lock: used to lock up the breaking button of circuit breaker and maintain the button at a pressed status; at this time, the circuit can’t be closed;
6. Transparent shield: used to enhance the level of protection;
7. Counter: used to count the total times of mechanical operation for circuit breaker;
8. Position signal of drawer-type circuit breaker: indicates the position of drawer-type circuit breaker in the drawer seat;
9. Door interlock: Prevent the cabinet door from being opened(status door interlock used to prevent the cabinet door from being opened when the circuit breaker is  switched  on; position door interlock used to prevent the cabinet door from being opened when the circuit breaker is in test and connection positions);
10. Mechanical interlock for wire cable: Used to interlock two circuit breakers, so that when one circuit breaker is switched on, the other one can’t be switched on;
11. Automatic change-over switch of double power supply: it functions for changeover of double power supplies.

What are the accessories available for NB1-63?

1. XF9 Auxiliary contact
2. XF9J Alarm contact
3. S9 Shunt release
4. V9 Undervoltage release

What are the accessories available for DZ158-125?

AX-1 Auxiliary contact

What are the accessories available for NC1?

1. F4 Top mounted auxiliary contact
2. F5  Air time delay contact
3. NCF1-11C Side mounted auxiliary contact
4. SR2 Surge Suppressor
5. Mechanical interlock

What are the accessories available for NC8?

1. F4 Auxiliary contact(for common NC8)
2. F5 Air time delay contact
3. F8 Auxiliary contact(for small-sized NC8-*M)
4. NCF8 Side-mounted auxiliary contact (for common NC8)
5. SR8 Surge suppressor
6. Mechanical interlock

What are the accessories available for NS2?

1. NS2-UV***, UVT-6/*** Undervoltage release
2. NS2-SH***, SHT-6/*** Shunt release
3. NS2-AE**, NS2-AU** Transient auxiliary
4. NS2-FA****, AL-6/**** Fault signal contact and transient auxiliary contact
5. NS2-MC　Water-proof mounting box
6. NS2-MC01　mounting box with emergency stop

What are the accessories available for NM8?

1. SM5, SM6, SQ5 and SQ6　Shunt release
2. UM5, SM6, SM7, UQ5, UQ6 and UQ7　in undervoltage release
3. AX　Auxiliary contact
4. AL　Alarm contact
5. Front-panel connection plate
6. Back-panel connection accessory
7. Plug-in base
8. Rotary operating mechanism
9. DIN rail adapter
10. Power operating mechanism
11. Mechanical interlock
12. Lock system
13. Terminal shield.

Maintenance and overhaul of NA1 air circuit breaker

1. Before maintenance and overhaul, the following procedures shall be conducted:
2. Ensure that the circuit breaker’s main circuit and secondary circuit are powered off;
3. Open the circuit breaker to check whether spring of the operating mechanism is released;
4. For a drawer-type circuit breaker, draw it out from the drawer seat, but for a fixed type circuit breaker, turn off the knife isolating switch;

Maintenance of circuit breaker (at least once half a year):

1.  Ensure that the ambient environment of a circuit breaker meets general provisions;
2.   All frictional and rotary components shall be lubricated regularly;
3.   Check whether the bolt at the connection between circuit breaker and busbar is screwed tightly and whether they are properly contacted;
4.   Check whether the terminal of the circuit breaker’s secondary loop is properly connected;
5.    Check whether the circuit breaker’s intelligent controller is properly displayed;
6.    Check whether the setting value for protective features of intelligent controller is correct;
7.    Check whether the on/off indication of circuit breaker is correct and reliable.

Inspection and repair of circuit breaker (at least once a year):

1.  Check whether all parts of the circuit breaker are complete and correct, for example, shell, chassis and other insulating parts;
2.   Check whether the circuit breaker’s base is securely connected with the baseboard, and no vibration in operation
3.   Manual on-off mechanism should be flexible and free of obstruction, and auxiliary switch changeover of secondary circuit shall be reliable and correct;
4.   Shake-in and shake-out the drawer seat manual; separation, test, position for connection shall be correct, interlock shall act reliably;
5.    Actions of shunt tripper, closing electromagnet and undervoltage tripper shall meet technical regulations of products, and the power operating mechanism should act normally, after secondary circuit is energized,
6.   For contact system of arc extinguish chamber: complete contact finger, correct position, sound silver coating, clean inside the chamber (note: don’t switch on/off the mechanism when cleaning the arc extinguishing chamber);
7.   Circuit breaker and connecting busbar are reliably connected, and the bolt shall be screwed tightly;
8.   Check whether the contact surface between the circuit breaker and the drawer seat is clean and correct; if not, clean the surface to ensure that there is no surface dusk or oxide, and the connection is reliable;
9.   Once overhauled, use a 500V megohmmeter to test the circuit breaker’s insulating resistance, and the resistance shall not be smaller than 20 megohms under ambient medium temperature of 20℃±5℃ and relative humidity of 50% to 70%.

Installation, use and maintenance of NM8 series plastic shell circuit breaker

1.  To use a copper conductor or a copper busbar, the standard section shall be subject to corresponding manual.
2.  Installation:

• Before installation, please check whether the circuit breaker and related parameters meet the use requirements and then secure the circuit breaker onto an installation board;
• Select a copper conductor of a section as stipulated in Article 1, strip away a proper length of insulating outer shell, insert it into the hole, press the wire ferrule, connect the wire ferrule and the circuit breaker with a bolt, and screw the bolt tightly; if a copper busbar is selected, connect the terminal board to a circuit breaker at first and then secure the connection;
• Insert a phase partition or terminal shield, or else, user has to undertake corresponding consequences;
• Check whether fixing and connection parts are secure and reliable; the circuit breaker shall be flexible and reliable when operated repeatedly.

Use and maintenance: (only persons with corresponding electrical professional qualifications permitted)

1.  Check the operation status of a circuit breaker regularly to clear away dusts on shell surface and maintain good insulating property;
2.  The circuit breaker’s tripping features are preset by the manufacturer and no need to make adjustment generally. To adjust the features as per requirements, customer shall cut off the power at first and then adjust the overload protection knob and the short-circuit protection knob until the requirements are met;
3.   If the circuit breaker is opened for overload, short-circuit and undervoltage protection, it’s necessary to identify causes and solve the problem before closing the circuit breaker;
4.   Be sure to prevent rainwater and falling when a circuit breaker is in use, storage and transport.

Safety notes for NJR2 soft starter

1.  A soft starter can be only installed by professionals;
2.  Before operating any live parts of the product, make sure to cut off the power supplies R, S and T in the main circuit and the power supply of the control circuit;
3.  Before a product is loaded, make sure that the data in F19 is consistent with the rated current of a motor nameplate;
4.  When installing a live conductor onto external product, please treat the exposed conductor part for insulation to avoid electric shock accident;
5.  If an external control terminal(2-wire) is adopted and set with auto restart function, then automatic restart will be seen when power is restored after cutoff or when a fault is cleared. This will endanger the safety of some machines. Please add interlock circuits to meet safety specifications of machines or devices;
6.  Before leaving the factory, a product has been strictly tested with dielectric test. However, in order to avoid unexpected shell electric leakage, please make sure that the earth terminal is securely grounded and the product meets relevant requirements;
7.  If external bypass contactor is used, then for each pole of the contactor, input U1, V1 and W1 must correspond to output U, V and W respectively; or else, power supply short circuit may occur when the product is changed to a bypass, finally burning the whole system;
8.  Hold the ENTER key before energization, to reset the parameters to factory default value;
9.  If a soft starter controls multiple motors, please confirm that the date in F02 is zero.

Safety notes for NVF2 transducer

1.  A transducer can be only installed, wired, debugged and examined by professionals;
2.  Don’t open the cover plate until the transducer is powered off or stops running to avoid electric shock accident;
3.  Don’t run the transducer when the cover plate is disassembled to avoid electric shock accident due to contact with high voltage terminal and charging part;
4.  Even when power is cut off, don’t disassemble the cover plate unless for wring and routine examination purposes. Or else, unexpected touch of the charging loop may result in electric shock accident;
5.  Test the + – DC busbar voltage with a multimeter after the power is cut off for at least 10 minutes, and the wiring or examination operation may be conducted only when the tested voltage is less than 15V;
6.  Please make sure that the earth terminal is securely grounded and the product meets relevant requirements;
7.  Don’t touch a transducer with a wet hand to avoid electric shock;
8.  Don’t replace a fan until power is off. It’s dangerous!
9.  Don’t connect a resistor to DC terminal + – directly, or else, it may cause a fire;
10.  In case of transducer failure, please cut off the power supply at the input side, or else, continuous large current may cause a fire;
11.  It’s strictly forbidden to connect the power cord to a terminal other than R, S and T, or else, the transducer may be damaged;
12.  Neither install a power capacity or a surge absorber nor connect a resistive load at the output end of a transducer;
13.  For each terminal, only voltage values stipulated in the user manual are permitted to avoid cracking or damage;
14.  Make sure that power cable is correctly connected to a corresponding terminal, to avoid cracking or damage;
15.  Always ensure correct polarity in connection to avoid cracking or damage;
16.  Don’t touch the transducer when power is on or power is cut off for just only a while; high temperature transducer may scald you.

Notes for power transformer: major components

1.          Main body: including iron core, winding, insulating element and lead wire;
2.          Voltage regulator: i.e., tap-switch, including non-excitation voltage regulation and on-load voltage regulation;
3.          Oil tank and cooling device;
4.          Protective device: inclusive of oil conservator, safety gas duct, moisture absorber, air relay, oil purifier and temperature measuring device;
5.          Insulating bushing

What is the function of transformer oil?

Transformer oil is used for insulation and cooling;

And for arc blowout in on-load tap changer;

What is the function of oil conserver?

Oil conserver is used to regulate the oil level, so that the transformer oil tank is always fully filled;

And to reduce the area of the contact surface between oil and air, so that oil will not be damped or oxidized at a very fast speed.

What is the function of transformer bushing? what are the requirements for it?

The function of transformer bushing is as follows:

It leads the high-voltage and low-voltage wire leads inside the transformer to outside the oil tank; it insulates the leads against the ground and fixed the leads. Transformer bushing is one of the current-carrying components of transformer. It conducts load current for long in the transformer operation and conducts short-circuit current when short circuit occurs outside the transformer.

The requirements for transformer bushing are as follows:

1.  Specific electrical strength and sufficient mechanical strength must be available.
2.  Good thermal stability; withstand the instantaneous superheat when short circuit occurs.
3.  Small size, light weight, good sealing performance and versatility, as well as easy maintenance.

What are the two types of transformer test items? What are their contents?

Transformer test is generally divided into insulation test and performance test.

Insulation test includes insulation resistance and absorption ratio test,  dielectric loss tangent value test, leakage current test, transformer oil test, industrial frequency withstand voltage and induction withstand voltage test; local discharge test is required for a transformer with Um of no less than 220kV. Full wave and operating wave impact test is required for online terminal with Um of no less than 300kV.

Performance test includes tests of transformation ratio, wiring group, DC resistance, idle load, short circuit, temperature rise and sudden short circuit.

What is the purpose of DC resistance test of transformer?

The purpose of DC resistance test is to check whether there is short circuit, open circuit or wrong connection in winding loop, whether there are poor contacts in welding point of winding loop wire, lead wire bushing and tapping switch. Besides, it can be checked whether the lead wire used for winding meets the design requirements.

What is the purpose of idle load test of transformer?

The purpose of idle load test is to test the no-load current and no-load loss in iron core, find partial or total defects in the magnetic circuit, and check whether winding has turn-to-turn fault after induction withstand voltage test of transformer.

Why does transformer winding need to be dried?

The purpose of drying is to improve the insulation level of winding. Insulating cardboard can be compressed under certain pressure F, and the mechanical strength of the winding will be improved.

What are the commonly-used insulation materials of Grade A? What is the heat-resistant temperature?

Commonly-used insulation materials of Grade A for transformer are insulating cardboard, cable paper, yellow painted silk, phenolic cardboard, wood and transformer oil, etc.

Heat-resistant temperature is 105℃.

Why does vacuum drying transformer have better effect?

Under vacuum condition, the higher the vacuum degree is , the lower the boiling point of the water molecules will be; and heated water is easily evaporated. The water volatilized from the transformer is rapidly drawn out by vacuum pump, thereby speeding up the evaporation of water, so this method has a good effect.

What are the requirements for parallel running of transformers? What are the consequences if they are not met?

The parallel running of transformers should meet the following conditions:

1.   The same connection group mark number (connection group);
2.    Equal rated primary voltages and rated secondary voltages, i.e. equal transformation ratios.
3.    Equal impedance voltage per unit (or percentage)

If they are not met, the consequences are:

1.    If the connection group mark numbers (connection groups) are different, the phase difference between the secondary voltages will be very large, and there will be heavy current in the secondary circuit; the larger the phase difference is, the heavier the circulating current will be; and the transformer will be definitely burned out.
2.    If the rated primary voltages and the rated secondary voltages are respectively different, i.e. different transformation ratio, there will be circulating current in secondary circuit; it will occupy the transformer capacity and increase the wear.
3.    Different impedance voltages per unit (or percentages) will lead to unreasonable load distribution; and there will be the circumstance that one is fully loaded while the other is under-loaded or overloaded.

What measures should be taken for open core hanging of transformer?

Open core hanging should be conducted in fine weather and the relative air humidity should be lower than 75%. The part of core exposed in the air should be lower than 12h when the relative air humidity is lower than 75%. Core of no more than 16h can be exposed if the relative air humidity is lower than 65%. Effective measures should be taken to prevent dust and rain from the transformer. If the ambient temperature is higher than the core temperature, leave the core resting f the ambient temperature or a while before hanging it out, or heat the core to 10℃ higher than the ambient temperature when necessary.

What are the main equipment and materials used in the transformer core hanging?

1.   Lifting equipment: crane, U-rings, steel wire slings, ropes, and wood, etc.;
2.   Oil containers and oil filtering equipment;
3.   Electric welding equipment;
4.   General tools and special tools;
5.    Cloth belt, dry insulating cardboard, cable paper, etc.;
6.    Ladder;
7.    Fire-fighting equipment;
8.    Megohm meter, double-bridge resistance meter and thermometer, etc.

What foreign certification does the company have received?

Part of the company's products have passed:

Which products have UL certification, accreditation, or are listed?

NC1/CJX2, NC6, NC8, NC2, NCK3, NCK5, NR2, NRE8, NS2-25, ND16, NP2/NP4, JQX-10F, JQX-13F, NJX-13FW, JZX-22F, JSZ3, NJS1, KG10D/KG10M, XJ3, NJB1,NB1-63,CB-125,YBLX-P1.

Which products have KEMA certification?

NC1, NC7, NC8, NM1, NM7, NM8, NA1, NA8G, NR2, NP2, NBH8-40, NB1L, Ex9CBL-N/Ex9CBL-H, NZ7, NH40, MES(BH-0.66), 138kV 45MVA transformer, 230kV 45MVA transformer, 230kV 250MVA transformer, 145kV GIS, 24kV Switchgear Panel, NV Series Indoor Vacuum Circuit Breaker.

Which products have CESI certification?

230kV 45MVA transformer, 150kV 80MVA transformer, 132kV 40MVA transformer.

Which products have DNV marine certification?

NB1-63、NM8-125～1250/NM8S-400～630

What international standards do products of the company comply with?

What is the difference between UL certification, UL accreditation and UL listing?

UL certification adopts American standards, and the product performance only covers North America and Japan, etc, and it is not applicable to Europe and other regions.

UL accreditation adopts all kinds of corporate standards, IEC international standards or European standards; the performance of their products has a larger coverage including China.

UL listing only applies to complete products and all kinds of parts or devices replaced or installed on site by qualified personnel. Products that apply to UL listing service include household appliances, medical equipment, computers, commercial equipment, as well as the various types of electrical products in construction, such as such as power distribution systems, fuses, wires, switches and other electrical components. A UL Listed product generally has UL Listing mark on it. 

What are the common reasons why NA1 breaker cannot be closed?

1.  Under-voltage release is not energized or is damaged;
2.   Reset button on intelligent controller is not reset (protruded on the panel);
3.   The body of drawer-type breaker is not rocked into the connection position;
4.   Secondary circuit of drawer-type breaker has bad contact;
5.   The breaker fails to store energy;
6.   The mechanism interlock actions and breaker has been locked;
7.   The control voltage of closed electromagnet is lower than 85% of Us or closed electromagnet is damaged;
8.    Wrong connection of wires of user has lead to energized shunt release and tripping of the circuit breaker.

Drawer-type circuit breaker cannot be rocked to the “connection" position; what is the cause?

1.   Foreign matter has fallen into the drawer base and stuck the rocking mechanism or the rocking mechanism has jumping chain;
2.   The rated current of circuit breaker does not match that of drawer base;
3.   The operation is not in place; no “click" from two sides in the drawer base.

what are the common causes for contactor noise?

1.    Power voltage is too low;
2.    Magnetic system is skewed or mechanically stuck, which causes that the iron core cannot be pulled level;
3.    Iron core polar surface is rusted or has foreign matter (such as grease or dust) on it;
4.    Short-circuit ring of iron core is fractured.

What are the common causes for damage to the contactor coil?

1.    Low power voltage causes that iron core cannot be pulled normally, and the current in the coil will rise sharply, resulting in overheated and burnt coil.
2.    High power voltage (> 110% Us) leads to overheated and burnt coil.
3.    Foreign matter has fallen into the contactor, which has demagnetized contactor coil and caused too large gap; the magnetic circuit is not closed, the  coil is overheated and burnt.

What are the common causes for thermal relay malfunction?

1.    Setting current value is set too small;
2.    The starting time of motor is too long;
3.    The cross-sectional area of connection wire is too small;
4.    Strong shock and vibration;
5.    Frequent reversible operation and jogging.

Main causes for and solution to the malfunction of residual current circuit breaker:

1. Operating current is selected too small;

When selecting operating current, it should be higher than 2-4 times normal leakage current in circuit. If normal leakage current of the electronic equipment is larger, the equipment on each circuit cannot be too many, and the total leakage current should be lower than the rated non-operating current of RCD. For example, the leakage current of a desktop computer is 3-4mA, so the number of computers connected to 30mA RCD circuit should not be more than five.

2. Improper use of residual current circuit breaker may cause malfunction;

When a three-pole earth residual current circuit breaker is used in a three-phase four-wire circuit, as the normal operating current in neutral line does not go through zero sequence current transformer, residual current circuit breaker will action once single-phase load is started.

Solution: A three-pole four-wire or four-pole residual current circuit breaker must be used for a three-phase four-wire circuit.

3. Grounding of load-side neutral line behind the residual current circuit breaker causes malfunction;

Grounding of load-side neutral line of the residual current circuit breaker will lead normal operating current to the ground through the grounding point, causing malfunction of residual current circuit breaker.

Solution: Connect the grounding wire to the neutral line on the power side of residual current circuit breaker.

4. Leakage current and wire-to-ground capacitive current cause malfunction.

The load-side wire of residual current circuit breaker is long and is laid closely to the ground, and there will be heavy wire-to-ground capacitive current, which may cause malfunction. Or the earth leakage current may be heavy due to decreased insulation of load-side wire, causing malfunction.

Solution: Use residual current circuit breaker with high leakage operating current or raise the wires overhead

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