Views: 10 Author: Jason Zeng Publish Time: 2025-10-28 Origin: Site
Regarding Contact Voltage
The parameters of DC contactors are the core basis for selection, installation, and safe operation, covering three key dimensions: electrical performance, operating characteristics, and safety protection. This article focuses on a detailed analysis of the main contact voltage of DC contactors.
1、Switching Voltage（Usw） ("Usw" is not a universally accepted general code; in this article, it specifically refers to switching voltage.)
It refers to the DC voltage value that its main contacts can safely carry, make and break under rated conditions, and is a key parameter to ensure that no arc breakdown or equipment damage occurs during the switching process. To understand this parameter, the following core points should be grasped:
（1） Principle of voltage matching: The circuit voltage in practical applications must be lower than or equal to the switching voltage of the contactor. If the circuit voltage exceeds this value, it is easy to generate an inextinguishable arc between the contacts during switching, resulting in contact ablation or adhesion.
（2） Coordination with breaking current parameters: The switching voltage and breaking current jointly determine the power capacity of the contactor (P=U×I). The switching voltage of a DC contactor should be marked together with the breaking current, electrical life cycles and load type. Users should read the corresponding DC contactor data sheet in detail when selecting a DC contactor. For example: 750Vdc / 300A / 1000 cycles (resistive load); 1000Vdc / 250A / 1000 cycles (resistive load); 1500Vdc / 50A / 1000 cycles (resistive load).
（3） Consideration of inductive loads: If the load in a DC circuit is an inductive component such as a motor or inductor, a reverse electromotive force will be generated during switching. It is necessary to reserve a higher voltage margin (it is generally recommended that the actual voltage does not exceed 80% of the maximum switching voltage) or use a freewheeling diode to suppress peak voltage.
（4） Environmental factors: High temperature and humid environments will reduce insulation performance, so DC contactors with higher switching voltage should be selected appropriately.
2、Rated Operational Voltage（Ue）
The rated operational voltage (Ue) of DC contactor contacts is the core benchmark parameter for safety certifications (such as UL, CE, TÜV, CCC). Safety certifications have mandatory requirements for the making and breaking capacity (electrical life cycles) of DC contactors, and there are differences between different safety certifications. Here, GB/T 14048.4-2020 is taken as an example.
Making and Breaking Conditions for Making and Breaking Capacity of Different Utilization Categories
GB/T 14048.4-2020 Table 7
Making and Breaking Conditions for Conventional Operating Performance of Different Utilization Categories
GB/T 14048.4-2020 Table 10
The parameters in Tables 7 and 10 of GB/T 14048.4-2020 must be met simultaneously, and they are mandatory requirements. Generally, before conducting safety certification for DC contactors, manufacturers need to perform preliminary tests to determine the rated operating current (Ie) and rated operating voltage (Ue). Usually, the rated operating voltage (Ue) is lower than the maximum switching voltage. It is necessary to note the differences between "making and breaking capacity", "conventional operating performance" and "electrical life". Generally, DC contactor manufacturers only mark the number of "electrical life" cycles in the product data sheet, and different electrical life cycles correspond to different switching voltages, breaking currents, load categories and switching frequencies.
3、Rated insulation voltage（Ui）
■ The rated insulation voltage (Ui) of a DC contactor refers to the maximum voltage value that the contactor can withstand for a long time under specified conditions without insulation damage. It is a basic safety indicator for the design and selection of contactors, and is directly related to the safe operation of DC contactors.
■ The rated insulation voltage (Ui) is the "withstand voltage upper limit" of the contactor's insulation system, and its main functions include the following two points:
（1）Ensuring electrical safety: Preventing insulation breakdown caused by excessively high voltage, which may lead to accidents such as leakage and short circuits.
（2）Serving as a design benchmark: Parameters such as the insulation structure, creepage distance, and electrical clearance of the contactor must be designed based on the rated insulation voltage.
■ Notes:
（1）The voltage in the actual circuit (including the normal operating voltage and possible overvoltage) must be less than or equal to Ui; otherwise, the insulation performance will fail.
（2）It is not equal to the rated operating voltage (Ue) or the maximum switching voltage. Generally, Ui is higher than the maximum switching voltage, and the maximum switching voltage is higher than Ue.
（3）Environmental factors such as temperature, humidity, and pollution level will affect insulation performance. Even if the voltage does not exceed Ui, harsh environments may still cause insulation damage.
