A complete guide to purchasing universal changeover switches: from principle to selection and application (Part 3)

Key technical parameters of universal changeover switches

Correctly understanding and evaluating the technical parameters of universal changeover switches is the core link in the selection process. These parameters not only determine whether the switch can meet the application requirements, but also directly affect the safety and reliability of the system. The main technical parameters of universal changeover switches include electrical parameters, mechanical parameters, environmental adaptability parameters and other aspects, which need to be comprehensively considered.

Rated voltage and current are the most basic electrical parameters, which directly determine the load capacity of the switch. Different series of universal changeover switches have different rated values. For example, the LW5 series is suitable for circuits with AC 50Hz, voltage up to 500V, DC voltage up to 440V, and its agreed heating current is 16A. The LW6 series is mainly suitable for AC and DC circuits with AC 50Hz, rated working voltage up to 380V, DC voltage up to 220V, and rated current is usually 5A or less. Although the LW12-16 series is also suitable for circuits with AC 50Hz, voltage 380V and below, and DC voltage 220V and below, its rated current can reach 16A, and it can directly control three-phase squirrel cage asynchronous motors of 5.5KW and below. When selecting, it is necessary to ensure that the rated value of the switch is greater than or equal to the maximum expected value in the actual application, and leave a certain safety margin.

The making and breaking capacity reflects the ability of the switch to safely cut off the circuit under abnormal conditions (such as short circuit). This parameter is particularly important for applications such as motor control, because large surge currents will appear when the motor starts or stalls. The making and breaking capacity of the LW5 series switch for controlling motors is usually given in a table, and users need to select according to the specific load type. Generally speaking, switches used for motor control require higher making and breaking capacity than switches used for ordinary line conversion.

The operating frequency is another important parameter, which indicates the number of operations allowed by the switch per unit time. For example, the normal operating frequency allowed by the LW5 series is 120 times/h. For occasions that require frequent operation, such as machine tool control or test equipment, models that allow a higher operating frequency should be selected, otherwise the service life of the switch will be shortened or even lead to early failure. At the same time, applications with high operating frequencies also need to consider the material and structural design of the contacts to ensure sufficient electrical life.

Mechanical life and electrical life directly reflect the durability and reliability of the switch. Mechanical life refers to the number of operations that the switch can withstand without power, while electrical life refers to the number of operations under rated load. These two parameters are usually quite different. For example, the mechanical life of the LW5 series switch is 100×10⁴ times, while the electrical life is 20×10⁴ times. In practical applications, the life of the switch is also affected by many factors such as load type, environmental conditions, and operating mode. Therefore, appropriate margins should be reserved when selecting.

The number and combination of contacts determine the complexity of the circuit that the switch can control. The contact system of the universal changeover switch is usually composed of multiple sections. For example, the LW5 series has 1-16 sections to choose from, and the LW12-16 series master control switch has 1-12 sections with a total of 12 configurations. Each contact can have different on-off combinations. By superimposing multiple contacts, complex control logic can be achieved. When selecting, it is necessary to determine the required number of contacts and the combination method according to the actual control requirements, so as to meet the functional requirements and avoid unnecessary complexity and cost increase.

The operating angle and positioning characteristics are important parameters unique to universal changeover switches. Different types of switches have different operating angles. For example, the LW26 series has 30°, 45° and 90°. The positioning characteristics determine how the handle is held in different positions. Common positioning methods include:

- Single-point positioning: The handle has only one fixed position.

- Multi-point positioning: The handle can be fixed at multiple angles.

- Self-resetting: The handle automatically returns to its original position after being released.

- Positioning and self-resetting combination: Some positions are positioned, and some positions are self-resetting.