Factors Affecting Terminal Selection

Factors Affecting Terminal Selection

Terminal Blocks and Terminal Blocks
[Key words]
At present, the application of power supply terminals in electronic devices has become a trend, and power supply terminal devices themselves are also gradually increasing, and can carry greater power. As terminal terminals become larger in size, their importance in the function of the equipment becomes more prominent, and they play an increasingly important role in ensuring product features.

The continuous improvement of the circuit board technology has increased the current capacity of the terminal blocks installed on the panel. It has now exceeded the 110A limit and far surpassed the level of the previous product. This makes it possible to use which type of power supply wiring is used during the design process. The problem of terminals meeting system requirements becomes more complex. In addition, the method of measuring performance parameters in different regions is different, and there are even considerable differences in the nominal parameters given for the same products. Therefore, in order to achieve long-term reliability and ensure low costs, it is important to understand these differences.

Engineers must also consider another factor that is often overlooked, namely marketing considerations. Typically, the terminals are visible to the user, so the marketing department often expects the product to match the overall system's color and style in appearance.

The following describes in detail the important factors affecting the selection of the terminal block.

Power processing factors

One of the first things to consider is the device's power handling capability. Simply reading the data sheet does not guarantee accurate comparison data. Engineers must understand how the product performance data listed in the manual is tested and determined.

At present, UL, IEC, CSA, and DIN do not have uniform standards in determining the power and performance specifications of the terminal products. Users need to understand the differences between UL and IEC specifications. The specifications for terminal blocks manufactured in Europe use IEC standards, while those manufactured in the United States use UL standards.
The difference between the two standards is very large. Engineers who do not know how to measure a product's specifications will take considerable risks because the selected device may not meet the required power level, or the specifications of the selected device may far exceed the design requirements. In Europe, the current rating of the device is determined by monitoring the temperature of the metal conductor as the current increases. When the temperature of the metal pin is 45°C higher than the ambient temperature, the measurement personnel will use this current as the rated current value (or maximum current value) of the device. Another of the IEC specifications is the allowable current value, which is 80% of the maximum current. In contrast, the UL standard will use 90% of the current value when the metal conductor temperature is 30°C above the ambient temperature as the current rating of the device. It can be seen that the temperature of the metal conductor part is a very important factor in all applications. This is more important for industrial equipment. Because industrial equipment usually needs to work in environments with temperatures up to 80°C. If the terminal temperature is 30°C or 45°C higher than this temperature, the terminal temperature will exceed 100°C. Depending on the type of nominal value and the insulating material used for the selected device, the product must be operated at a current lower than the rated value so as to ensure that they can operate reliably within the desired temperature range. In some cases, materials suitable for compact packaged devices may not be able to meet the heat dissipation requirements well, so the current used for such terminal devices must be much lower than the rated value.

As companies globalize and need to design systems that can be sold globally, system designers are increasingly using power terminal products manufactured in other countries. Since Europe uses a nominal value measurement method, it is common practice in Europe to use the device below the nominal value in the design. However, many designers in the United States are not familiar with this concept. If you do not understand the differences between the standards, you will have difficulties in the design process.

Another factor that is often overlooked when selecting a device is the termination technology used by the product. Most power terminal products are still using through-hole connections. This method provides the required mechanical support and guarantees a solid electrical contact with the power plane embedded in the multilayer circuit board. There are many different types of pins used to connect the terminals to the circuit board. Some companies only offer single-pin models, others offer multi-pin products. The advantage of a multi-pin product is that it distributes the current more evenly across the board traces, providing more reliable mechanical stability and improved soldering firmness.

[I] appearance factor [/I]

Although the name "power terminal" does not sound beautiful, many companies believe it has played an important role in the appearance of the product and its affinity for users. The power terminals must be easily installed in the field because they are often mounted on the front of the easy-to-see product panel. In this way, marketers often want to have a say in the appearance of the power terminal products. But it is often the case that engineers design products that meet all mechanical and electrical parameters but have to change because they do not meet sales requirements. If this happens at the end of the design cycle (often when the marketing department sees the prototype for the first time), then a fierce debate can hardly be avoided and could lead to cost increases and delivery delays. In many industrial control systems, the terminals are often one of the few components that technicians need to pay special attention to. Although its user interface is relatively simple (mainly screws), it is very important for the normal operation of the equipment.

In general, as the current increases, the wires become thicker, and the torque required to fasten these thick wires to the terminals also needs to increase. Therefore, the power terminals require larger screws and a more rugged insulating housing. Sometimes small screws are used to save space. This is often the case in very compact terminal products. Some wires have a diameter of more than 1/4 inch, so these small screws are difficult to handle. When technicians and servicemen need to install multiple wires, using enough screws to simplify wiring can save time. This is why it is so important for engineers to listen to the opinions of the marketing department as early as possible in the design process. If the terminals must be properly polished or properly colored, it is much easier to propose these parameters as original product requirements than to adjust them at the end of the development cycle.

When the terminals are used in consumer products (such as high-end stereo products), the appearance becomes more and more important. In fact, some designers often specify that the terminal devices used for audio equipment be gold-plated. Although this increases the cost and does not significantly improve the performance, gold plating does improve the appearance of the product.


Understanding the measurement method of the power terminal parameters is a key part of the system design. Verifying that the selected power terminal satisfies the temperature range, current, and voltage requirements of the power supply helps ensure the long-term reliability of the system. In addition, if the selected power supply terminal device adopts a wiring technology that can meet the market requirements, and in the design to ensure the convenience of the user's operation, it will greatly increase the probability of success of the final product. â–