In the field of industrial automation and electrical control, modular contactors play a crucial role as key electrical components, widely used in motor control and the switching operations of various loads. As a specialized manufacturer of modular contactors, Denor, we are committed to providing high-quality products that meet the diverse needs of different industrial scenarios.
Technical Features of Denor’s Modular Contactors
Modular contactors, with their unique electrical connection capabilities and excellent operational stability, offer solutions for a wide range of complex electrical applications. First and foremost, the primary characteristics of modular contactors lie in their structural reliability and high efficiency in current control, making them ideal for power equipment that must be frequently switched on and off.
There are several types of modular contactors, including AC contactor types and DC contactor types. Whether your load requirements are for single-phase, two-phase, or three-phase connections, the modular design allows for flexible selection according to different circuit requirements. Our product range covers multiple pole configurations, including single-pole, double-pole, and three-pole options, catering to various electrical circuits. Furthermore, the control method for modular contactors is generally based on electromagnetic types, which simplifies operation. The next generation of installation contactors has introduced even higher precision in control on this foundation.
In modern electrical systems, the normal load and overload characteristics of modular contactors are also critical factors engineers must consider, ensuring safe operation. Additionally, the conditional short-circuit current capability is crucial; this not only involves protection safety for devices but also directly influences the reliability and stability of the entire electrical system.
Utilization Categories and Control Circuits
The utilization categories of modular contactors, such as AC-7a, AC-7b, AC-1, AC-3, etc., are essential for determining applicable conditions based on testing outcomes. During operation, by managing control circuits, the contactors enable greater automation control of mechanical equipment, achieving optimal operational performance.
Moreover, the configuration of auxiliary circuits enhances the multifunctionality of contactors. In the electrical control process, feedback and signal indication of device status are facilitated through auxiliary contacts, significantly improving maintenance and monitoring convenience in modern industrial equipment.
As a reputable modular contactor manufacturer Denor in the Chinese and Global market, we adhere to innovation and quality service, continually providing customers with more reliable products and solutions. We welcome businesses with needs to contact us and explore more possibilities in electrical control together.
To help electrical engineers and electricians quickly understand Denor’s modular contactors, we are sharing some commonly used terms related to the characteristics of contactors.
Summary of characteristics
The characteristics shall be stated in the following terms, where such terms are applicable:
- type of contactor (see 5.2);
- rated and limiting values for main circuits (see 5.3);
- utilization category (see 5.4);
- control circuits (see 5.5);
- auxiliary circuits (see 5.6);
- co-ordination with short-circuit protective devices (see 5.7).
Type of contactor
General
The following shall be stated (see also Clause 6):
Number of poles
Method of control
- automatic (by pilot switch or sequence control);
- non-automatic (e.g. by hand operation or by push-buttons);
- semi-automatic (i.e. partly automatic, partly non-automatic).
Rated and limiting values for main circuits
General
The rated values established for a contactor shall be stated in accordance with 5.3.2 to 5.4 and 5.7.
Rated voltages
A contactor is defined by the rated voltages given in 5.3.2.2 to 5.3.2.4.
Rated operational voltage (Ue)
A rated operational voltage of a contactor is a value which, combined with a rated operational current, determines the application of the contactor and to which the relevant tests and the utilization categories are referred.
For a single-pole contactor, the rated operational voltage is generally stated as the voltage across the pole.
For a multipole contactor, it is generally stated as the voltage between phases.
NOTE 1 A contactor can be assigned a number of combinations of rated operational voltages and rated operational currents or powers for different duties and utilization categories.
NOTE 2 A contactor can be assigned a number of rated operational voltages and associated making and breaking capacities for different duties and utilization categories.
NOTE 3 Attention is drawn to the fact that the operational voltage can differ from the working voltage (see 3.5.22) within a contactor.
Rated insulation voltage (Ui)
The rated insulation voltage of a contactor is the value of voltage to which dielectric tests voltage and creepage distances are referred.
In no case shall the maximum value of the rated operational voltage exceed that of the rated insulation voltage.
NOTE For contactors without a specified rated insulation voltage, the highest value of the rated operational voltage is considered to be the rated insulation voltage.
Rated impulse withstand voltage (Uimp)
The peak value of an impulse voltage of prescribed form and polarity which the contactor is capable of withstanding without failure under specified conditions of test and to which the values of the clearances are referred.
The rated impulse withstand voltage of a contactor shall be equal to or higher than the values stated for the transient overvoltages occurring in the circuit in which the contactor is fitted.
NOTE Preferred values of rated impulse withstand voltage are given in Table 16.
Currents or powers
A contactor is defined by the currents given in 5.3.3.2 to 5.3.3.4.
Conventional free air thermal current (Ith)
The conventional free air thermal current is the maximum value of test current to be used for temperature-rise tests of an unenclosed contactor in free air (see 9.3.3.3).
The value of the conventional free air thermal current shall be at least equal to the maximum value of the rated operational current (see 5.3.3.4) of the unenclosed contactor in eight-hour duty (see 5.3.5.2).
Free air is understood to be air in normal indoor conditions, reasonably free from draughts and external radiation.
NOTE 1 This current is not a rating and is not mandatorily marked on the contactor.
NOTE 2 An unenclosed contactor is a contactor supplied by the manufacturer without an enclosure or a contactor supplied by the manufacturer with an integral enclosure which is not normally intended to be the sole contactor protective enclosure. An unenclosed contactor is characterised by IP00.
Conventional enclosed thermal current (Ithe)
The conventional enclosed thermal current is the value of current stated by the manufacturer to be used for the temperature-rise tests of the contactor when mounted in a specified enclosure. Such tests shall be in accordance with 9.3.3.3 and are mandatory if the contactor is described as an enclosed contactor in the manufacturer’s catalogues and normally intended for use with one or more enclosures of specified type and size (see Note 2 of 5.3.3.2).
The value of the conventional enclosed thermal current shall be at least equal to the maximum value of the rated operational current (see 5.3.3.4) of the enclosed contactor in eight-hour duty (see 5.3.5.2).
If the contactor is normally intended for use in unspecified enclosures, the test is not mandatory if the test for conventional free air thermal current (Ith) has been made. In this case, the manufacturer shall be prepared to give guidance on the value of the enclosed thermal current or the derating factor.
NOTE 1 This current is not a rating and is not mandatorily marked on the contactor.
NOTE 2 An enclosed contactor is a contactor normally intended for use with a specified type and size of enclosure or intended for use with more than one type of enclosure.
Rated operational currents (Ie) or rated powers
A rated operational current of a contactor is stated by the manufacturer and takes into account the rated operational voltage (see 5.3.2.2), the conventional free air or enclosed thermal current, the rated frequency (see 5.3.4), the rated duty (see 5.3.5), the utilization category (see 5.4) and the type of protective enclosure, if any.
In the case of a contactor for the direct switching of individual motors or LED lamps, the indication of a rated operational current can be replaced or supplemented by an indication of the maximum rated power, at the rated operational voltage considered, of the load for which the contactor is intended. The manufacturer shall be prepared to state the relationship assumed between the operational current and the power.
Rated frequency
The supply frequency for which a contactor is designed and to which the other characteristic values correspond.
NOTE The same contactor can be assigned a number or a range of rated frequencies.
Rated duties
The rated duties considered as normal are given in 5.3.5.2 to 5.3.5.5.
Eight-hour duty (continuous duty)
A duty in which the main contacts of a contactor remain closed while carrying a steady current long enough for the contactor to reach thermal equilibrium but not for more than eight hours without interruption.
NOTE 1 This is the basic duty on which the conventional thermal currents Ith and Ithe of the contactor are determined.
NOTE 2 Interruption means breaking the current by operating the contactor.
Intermittent periodic duty or intermittent duty
A duty with on-load periods, during which the main contacts of a contactor remain closed, having a definite relation to off-load periods, both periods being too short to allow the contactor to reach thermal equilibrium.
Intermittent duty is characterized by the value of the current, the duration of the current flow and by the on-load factor which is the ratio of the in-service period to the entire period, often expressed as a percentage.
According to the number of operating cycles which they are capable of carrying out per hour, contactors are divided into the following preferred classes:
| – class | 1: | 1 | operating cycle per hour; |
| – class | 3: | 3 | operating cycles per hour; |
| – class | 12: | 12 | operating cycles per hour; |
| – class | 30: | 30 | operating cycles per hour; |
| – class | 120: | 120 | operating cycles per hour; |
| – class | 300: | 300 | operating cycles per hour; |
| – class | 1 200: | 1 200 | operating cycles per hour. |
A contactor intended for intermittent duty can be designated by the characteristics of intermittent duty.
EXAMPLE An intermittent duty comprising a current flow of 32 A for 2 min within every 5 min can be stated as: 32 A, class 12, 40 %.
Temporary duty
Duty in which the main contacts of a contactor remain closed for periods insufficient to allow the contactor to reach thermal equilibrium, the on-load periods being separated by off-load periods of sufficient duration to restore equality of temperature with the cooling medium.
Periodic duty
A type of duty in which operation, whether at constant or variable load, is regularly repeated.
Normal load and overload characteristics
This subclause gives general requirements concerning ratings under normal load and overload conditions.
Detailed requirements are given in 8.2.4.
Ability to withstand motor switching overload currents
A contactor intended for switching motors shall be capable of withstanding the thermal stresses due to starting and accelerating a motor to normal speed and due to operating overloads.
Requirements to meet these conditions are given in 8.2.4.4.
Rated making capacity
Requirements for the various utilization categories (see 5.4) are given in 8.2.4.2. The rated making and breaking capacities are only valid when the contactor is operated in accordance with the requirements of 8.2.1.1 and 8.2.1.2.
Rated breaking capacity
Requirements for the various utilization categories (see 5.4) are given in 8.2.4.2. The rated making and breaking capacities are only valid when the contactor is operated in accordance with the requirements of 8.2.1.1 and 8.2.1.2.
Conventional operational performance
Specified as a series of making and breaking operations in 8.2.4.3.
Rated conditional short-circuit current
The rated conditional short-circuit current of a contactor is the value of prospective current stated by the manufacturer, that the contactor, protected by a short-circuit protective device specified by the manufacturer, can withstand satisfactorily for the operating time of this device under the test conditions specified in 9.3.4.
The details of the specified short-circuit protective device shall be stated by the manufacturer.
NOTE The rated conditional short-circuit current is expressed by the RMS value of the AC component.
Utilization category
General
The utilization category of a contactor defines the intended application and is characterized by one or more of the following service conditions:
- current(s), expressed as multiple(s) of the rated operational current;
- voltage(s), expressed as multiple(s) of the rated operational voltage;
- power-factor.
The standard utilization categories are given in Table 1.
Each utilization category is characterized by the values of the currents, voltages, power-factors and other data of Table 7 and Table 9 and by the test conditions specified in this document.
It is therefore unnecessary to specify separately the rated making and breaking capacities as these values depend directly on the utilization category as shown in Table 7.
Unless otherwise stated, contactors of utilization category AC-7b are designed on the basis of the starting characteristics of the motors compatible with the making capacities of Table 7. When the starting current of a motor, with stalled rotor, exceeds these values, the operational current should be decreased accordingly.
Assignment of utilization categories based on the results of tests
A contactor which has been tested for one utilization category or at any combination of parameters (such as highest operational voltage and current, etc.) can be assigned another utilization category without testing provided that the test currents, voltages, power-factors, number of operating cycles, ON and OFF times given in Table 7 and Table 9 and the test circuit for the assigned utilization category are not more severe than those at which the contactor has been tested and the temperature-rise has been verified at a current not less than the highest assigned rated operational current in continuous duty.
Table 1 – Utilization categories
| Utilization categories a | Typical loads |
| AC-7a | Slightly inductive |
| AC-7b | Motor b |
| AC-7c | Switching of compensated electric discharge lamp control c |
| AC-7d | LED lamp |
| a Contactors can have other utilization categories, in which case they shall comply with the requirements of IEC 60947-4-1 for such categories.b The AC-7b category can be used for occasional inching (jogging) or plugging for limited time periods; during such limited time periods the number of operations should not exceed 5/min or more than 10 in a 10-minute period. c This category is similar to a capacitive switching category AC-6b as defined in IEC 60947-4-1 for the switching of capacitor banks, the characteristic being very dependent on the capacitance value of the lamp circuit. | |
Control circuits
The characteristics of control circuits are:
- kind of current;
- rated frequency;
- rated control circuit voltage Uc (nature and frequency);
- rated control supply voltage Us (nature and frequency), where applicable;
- suitability to be connected to SELV circuits.
NOTE A distinction has been made above between the control circuit voltage, which would appear across the “a” contacts (see 3.3.10) in the control circuit, and the control supply voltage, which is the voltage applied to the input terminals of the control circuit of the contactor and which can be different from the control circuit voltage owing to the presence of built-in transformers, rectifiers, resistors, etc.
The rated control circuit voltage and rated frequency, if any, are the values on which the operating and temperature-rise characteristics of the control circuit are based.
Auxiliary circuits
The characteristics of auxiliary circuits are the number and kind of contacts (“a” contact, “b” contact, etc.) in each of these circuits and their ratings according to IEC 60947-5-1.
The characteristics of auxiliary contacts and switches shall comply with the requirements of IEC 60947-5-1.
