The Ultimate Guide to Terminal Block Selection

What is a Terminal Block?

A terminal block consists of a modular housing with an insulated body that secures two or more wires together. Terminal blocks—also referred to as terminal connectors, connection terminals, or screw terminals—are used in a wide array of applications where electrical systems need to be safely connected. They are ideal for designs requiring secure, well-organized, and semi-permanent wire connections that can be easily swapped out for inspection or repair in the field.

Terminal Block Types  

Terminal blocks come in various types, each suited for specific applications. Below are some of the most common types:  

PCB Mount  

Also known as Eurostyle or wire-to-board terminal blocks, PCB mount types work by inserting bare wires into the module, where a clamp secures the wire within the housing. The housing is soldered to a PCB using standard footprints. These terminal blocks are available as single, dual, or multi-level modules.  

Barrier Strips  

Barrier strips feature screw-down terminals where a ring or spade terminal attached to the wire is inserted onto the screw and tightened. They are commonly used in environments where vibration is a concern due to their secure connection.  

Feed-Through/DIN Rail  

Feed-through terminal blocks are designed for wire-to-wire connections, with one input and one output contact allowing two distinct wires to be connected on opposite sides of the housing. These terminal blocks can also be single, dual, or multi-level modules. Feed-through types are often mounted on DIN rails. DIN rail terminal blocks are available in feed-through styles for wire connections or ground types, which appear similar but ground incoming wires to the DIN rail or panel.  

Key Terminal Block Electrical Considerations  

When designing a system utilizing terminal blocks, it's essential to consider factors beyond the system's voltage and current requirements. Below are key considerations:  

Current Rating  

The current rating is a critical parameter, influenced by the terminal's conductivity, cross-sectional area, and heat rise. Operating beyond the rated current can cause overheating and damage, posing safety risks. To ensure reliability, select a terminal block rated for at least 150% of the system's maximum expected current.  

Voltage Rating  

The voltage rating is determined by the dielectric strength and pitch of the terminal block housing. The system's maximum operating voltage must not exceed the terminal block's rating. Voltage surges should also be considered when choosing a suitable block.  

Pole Count  

Pole count refers to the number of individual circuits in a terminal block. Options range from a single pole to 24 poles or more, depending on the application's circuit requirements.  

Pitch  

Pitch is the center-to-center distance between adjacent poles in the terminal block. It is often dictated by the voltage/current ratings and factors like creepage and clearance. Common pitches include 2.54 mm, 3.81 mm, 5.0 mm, and 7.62 mm.  

Wire Size/Type  

The terminal block's voltage/current rating determines the minimum and maximum wire sizes it can accommodate. Ensure the chosen wire size fits the terminal block and consider wire type. Stranded or multi-core wires are commonly used for screw terminals, while single-core wires are preferred for push-in terminal blocks. Wire sizes are specified in American Wire Gauge (AWG) in North America or in mm² elsewhere.  

Key Terminal Block Mechanical Considerations  

Beyond electrical factors, mechanical considerations play a critical role in terminal block design. These considerations include housing restrictions that affect footprint, orientation, and connection accessibility. Key mechanical variations include:  

Wire-Entry Orientation  

Terminal blocks are commonly available in three orientations: horizontal (90°), vertical (180°), and 45°. The choice of orientation is often dictated by physical design constraints that make one configuration more practical than others.  

Wire-Securing Methods  

Wires are typically secured in terminal blocks using one of three methods:  

- Screw Terminal: Tightening a screw clamps the wire against the conductor.  

- Push Button: A spring clamp is opened by pressing a button; releasing the button secures the wire.  

- Push-In: Wires are directly pressed into the housing, where a spring clamp secures them without a button.  

Module Type  

Terminal block modules are available in interlocking or single-piece designs:  

- Interlocking Modules: Constructed in 2- or 3-pole units that snap together to create the desired pole count. DIN rail terminal blocks also operate this way, sliding onto the rail and finishing with an end cap.  

- Single-Piece Modules: All poles are housed in one unit, ideal for applications like pluggable housings or high-current and high-temperature scenarios requiring stronger construction.  

Wire-to-Housing Method  

Most terminal blocks have wires inserted directly into the housing. Pluggable terminal blocks, however, offer modular housings that plug into fixed housings on a PCB. These are ideal for designs requiring frequent disconnection without the need to remove individual wires.  

Conclusion

While there are many factors to consider when designing an overall system, terminal blocks are an optimal solution for complex electrical system connections. With a variety of color options and configurations, RHT's terminal blocks offer a range of options to meet your design challenges.