In modern electronic and electrical systems, terminal blocks are key components that ensure stable, secure, and efficient electrical connections. With the advancement of technology and the diversification of application fields, the design and selection of terminal blocks have become increasingly important. Choosing the right terminal block not only helps improve the overall system performance but also reduces the risk of failure, simplifies maintenance processes, and extends the lifetime of equipment. Therefore, understanding the various types of terminal blocks and the considerations in design and application is a necessary step in achieving efficient and reliable electrical connections. This article will introduce the types of terminal blocks, the considerations when choosing them, and the features of terminal blocks offered by Same Sky.
Diversified types of terminal blocks available to suit application needs
In industrial automation and other applications, many devices require stable and secure wiring systems, where terminal blocks can be used to connect wires efficiently and enhance overall system safety. Terminal blocks consist of modular housings and an insulated body that securely fastens two or more wires together. Also known as terminal connectors, connection terminals, or screw terminals, they are widely used in applications requiring safe connections within electrical systems. They are ideal for designs that need secure, well-organized, semi-permanent wire connections and can be easily replaced for field inspections or repair.
The types of terminal blocks are quite diverse and can be selected based on the application's needs. Various types of terminal blocks can be used in designs, including PCB mount, barrier strips, feed-through/DIN rail, and others.
PCB mount terminal blocks, often referred to as Eurostyle or wire-to-board terminal blocks, operate by inserting bare wires into the module, securing the wires in the housing with clamps, and then soldering the housing to a PCB of common footprints. PCB mount terminal blocks can come as single, dual, or multi-level modules.
Barrier strips, on the other hand, feature a screw down terminal where ring terminals or spade terminals are attached to the wires, then inserted onto the screw and tightened into the housing. Barrier strips are typically used in environments where vibration is a consideration. Additionally, another type, the feed-through/DIN rail terminal block, is used to connect two wires together for wire-to-wire connections. This type of terminal block has one input and one output contact, with the two distinct wires fed into opposite sides of the housing. Like PCB mount versions, these modules can also come in single, dual, or multi-level configurations. Feed-through style is most commonly found in DIN rail-mounted configurations. DIN rail terminal blocks are typically offered as a feed-through type for wire-to-wire connections or ground types, which visually appear similar to feed-through style but instead of connecting incoming wires, they ground them to the DIN rail or panel.
Key electrical considerations for terminal blocks
When designing a system that will use terminal blocks, it is important to understand the system's overall voltage and current requirements, as well as other factors such as the pole count, pitch, and wire size/type.
Firstly, the current rating is typically the most crucial parameter to consider when designing with terminal blocks. The current rating is based on factors such as the terminal's conductivity, cross-sectional area, and corresponding heat rise. Operating at currents that are too high may cause the terminal block to overheat and become damaged, leading to significant safety issues. A best practice is to use a terminal block with a rated current of at least 150% of the system's expected maximum current.
The voltage rating, on the other hand, depends on the dielectric strength and pitch of the terminal block's housing. The maximum system voltage applied must be less than the voltage rating, and any voltage surges in the system should also be evaluated when selecting terminal blocks. Additionally, the number of individual circuits within the terminal block, known as the pole count, can range from as few as a single pole to as many as 24 poles or more, depending on the specific application.
The pitch of the terminal block is defined as the center-to-center distance from one pole to the next. The pitch of the connector is typically determined by the overall ratings of the terminal block, which takes into account factors such as voltage/current, creepage, and clearance. Common industrial pitches include, but are not limited to, 2.54 mm, 3.81 mm, 5.0 mm, and 7.62 mm.
The minimum and maximum wire size that a terminal block can accept is a corresponding function of the voltage/current rating. Besides ensuring that the wire used physically fits into the terminal block, the type of wire should also be considered. Stranded or multi-core wire is usually used with screw terminals, while solid-core wire is commonly used with push-in style terminal blocks. In North America, wire sizes are specified in American Wire Gauge (AWG), but wire size can also be specified in mm2.
Key mechanical considerations for terminal blocks
In addition to electrical factors, mechanical restrictions and limitations must also be considered in terminal block design. Key features to consider include any mechanical restrictions on the housing that may affect the overall footprint, orientation, and accessibility of the connections. Mechanical variations in the housing can include wire entry orientation, wire securing methods, module types, and wire-to-housing methods, among others.
There are three common wire entry orientations for terminal blocks: horizontal, vertical, and 45°. Horizontal and vertical are also referred to as 90° and 180°, respectively. The wire orientation can typically be determined by physical restrictions in the overall design, helping to decide which option is more feasible.
The method of securing wires within the terminal block housing is generally achieved through three main types: screw terminals, push-button terminals, and push-in terminals. Screw terminals, or screw-type terminal blocks, secure the wire against the conductor in the terminal block by tightening a screw that closes a clamp. Additionally, push-button terminals use a spring clamp to secure the wire against the conductor; pressing the button opens the spring clamp, and releasing the button clamps the spring onto the wire. Push-in terminals, similar to push-button terminals with spring clamps, allow the wire to be directly pressed into the housing without the need to use a push button to open the spring.
Terminal block modules can be constructed as interlocking components or in single housings. Interlocking terminal block modules are typically constructed in 2-pole and 3-pole versions. With these two sizes, designers can snap the modules together to achieve any pole count required. DIN rail terminal blocks operate in much the same way, with individual units sliding together on a metal rail. Once the desired configuration and number of poles are achieved, a compatible end cap is used to complete the setup, protecting the outermost unit's housing.
Single-piece terminal blocks are constructed with all poles contained within a single housing. These are typical features of pluggable housings, where multiple piece configurations are not possible. Other uses include high-current or high-temperature versions, where a single housing provides more robustness.
While most terminal block connectors allow wires to be directly inserted into the housing, there are some variations that use mating pairs that can be plugged together. These pluggable terminal blocks still allow wires to be inserted into the housing but offer the added benefit of a modular housing that can be directly plugged into a fixed housing on the PCB. These are ideal for designs that require frequent disconnection of the main connection without the need to disconnect all individual wires.
The safety rating of terminal blocks and other design considerations
Safety ratings are crucial when specifying terminal blocks. Terminal blocks are typically certified and/or designed according to UL and/or IEC safety standards and are made from materials that meet the flammability rating of UL94V-0. Both UL and IEC ratings may appear differently on datasheets because each agency uses different standards, and the terminal blocks must meet their respective requirements. When selecting terminal blocks, it's important to understand the overall system safety requirements and ensure that the terminal block ratings comply with these requirements.
To make assembly or maintenance easier for users, housing colors or special markings can be modified to help distinguish between different terminal block connections. This is particularly useful in complex systems with multiple wiring and circuits housed in a centralized location. Additionally, the operating temperature of the end system should be considered when selecting terminal blocks to determine if high-temperature rated terminal blocks are necessary.
Same Sky is a key supplier of terminal blocks, offering pluggable, screwless, screw-type, and DIN rail configurations with up to 24 pole counts, various color options, and wire gauges ranging from 28 to 4 AWG. Same Sky’s terminal block connectors also feature various UL and IEC current and voltage ratings, along with an operating temperature range of -40 to 105°C, and they offer high-temperature terminal blocks rated up to 130°C.
Conclusion
While many factors need to be considered when designing an entire system, terminal blocks are the best solution for connecting complex electrical systems. Understanding the characteristics and functions of different types of terminal blocks is crucial when selecting them. Choosing the right terminal block not only affects the stability and safety of the electrical system but also relates to the ease of maintenance and the long-term service life of the system. By considering specific application requirements, operating environments, material selection, and installation convenience, designers can choose the most suitable terminal block, thereby enhancing the overall performance and reliability of the system. Same Sky’s terminal blocks offer various color options and configurations, providing a range of choices to meet your design challenges.