Plan for sustained use of the maximum current rating

The current rating is often the first and most important parameter while selecting a terminal block. The current rating is based on the conductivity of the terminals and cross-sectional area. Overheating and damage to the terminal block can result from operating at too high a current, causing severe safety hazards. It is best practice to use a terminal block that is rated for at least 120 times of the maximum current per cross section of the wire size used, for a connection which is expected in the system.

Voltage rating

The dielectric strength and pitch of the terminal block determine the voltage rating. The application's maximum system voltage must be less than the voltage rating. When selecting the terminal block, voltage ratings of the system should also be considered.

Look at the number of connections or levels required

The number of individual poles within the terminal block is also known as the number of connections. This can vary as per your user’s requirements. Usually, the minimum number of connection points or poles are two. Similarly, there are also multiple level terminal blocks where multiple connection points are available at multiple levels. This feature can help you save space in electrical panel designs which have dense wiring applications.

Recognise the influence of wire type, size and rating

The voltage and current rating would be influenced by the minimum and maximum wire sizes that the terminal block can take. In addition to making sure the wires used will properly fit into the terminal block, the type of wire should also be considered. Stranded, flexible or solid wires are typically used for terminal blocks. Multiple wires with lugs or ferrules can also be accommodated within the terminal block, which should also be considered while selecting the range of terminal block. The wire size or wire ratings are selected as per IEC and UL standards, depending on the specifications required.

Save panel space by knowing pitch or width of the Terminal Block

The pitch of a Terminal Block is defined as the centre distance between poles of the terminal blocks. The pitch is decided by the overall rating of the terminal block, which takes into account considerations like as voltage/current, creepage, and clearance. The pitch of the terminal blocks vary from terminal to terminal depending upon the size of the wire conductor used. Pitch is considered as an important selection factor today, as it helps the electrical project designer to accommodate more terminals in an electrical panel with space constraints.

Wire-entry orientation

Terminal blocks are available in three common wire orientations: Side, Top, and Angular.

- In side entry orientation the wires are terminated into the terminal block through a guided side entry.

- In top entry orientation, the wire is installed from the top entry point next to the actuation of the connection point. Top entry terminal blocks are often used in panels where it is difficult for a wire to terminate from the side due to space constraints. Top entry connection method is often considered to be the best solution instead of a side entry Terminal Block.

- Angular terminal blocks are designed at a 45 degree angle to reduce stress on wires which cab be caused due to slacking. These kind of terminal blocks are often used for wires with higher cross-sectional areas. 

There are various connection methodologies that are prevalent in the electrical industry. Screw, Push-IN, Spring, Stud and Bolt, and Pluggable are some of the major connection technologies used to connect wires in terminal blocks.

• Screw Connection Technology: In this method the wire is terminated or fastened in the terminal block with the help of screws. This is a traditional connection technology and is widely used.

• Push-In Connection Technology: These terminal blocks accommodate the wires with the help of actuation springs inside the clamping units. In order to clamp a wire inside the terminal block, a spring is actuated by pressing the tab on the terminal block with the help of tool, the wire is then entered into the clamping unit and the spring is released for the wire to be safely and firmly connected into the terminal block.

• Spring Connection Technology: Here, the wire is held in with the help of the spring in the clamping unit. These terminal blocks offer the advantage that the person doing the wiring does not need an external tool to actuate the spring. The wire is simply inserted inside the clamping unit and the connection is achieved.

• Stud Bolt Connection: These terminal block are made up of a Stud and Bolt for terminating the wires. Various types of lugs can be used to connect the wires on the connection point. Usually these type of terminal blocks are used for wires with larger cross sections.

• Pluggable Connection: Terminal block used with this connection method comes with a pin. An external plug is used to achieve to form a connection with the base terminal. These type of terminals are mostly used in applications where there are frequent movements of the wire assembly.

Terminal blocks can be designed for various functions depending on the applications they are used in. Here are a few examples of terminal blocks defined by function:

• Feed-through: Offers regular termination points
• Fuse: For protection against surges in the system
• Ground: Offers ground connection
• Electronic components: These have inbuilt or pre-assembled terminal block functions such as Diode, Resistors, MOV or Varistor
• High voltage: For solar applications or voltages around 1500V
• Thermocouple: For high temperature applications

Always check the safety rating offered by manufacturer

Terminal blocks are certified and/or designed to IEC, UL and other safety standards. These terminal blocks are also compliant with various usage environments based on the tests they have undergone. This includes tests for flammability, climatic conditions, dielectric and temperature rise, etc., in accordance with IEC and UL Standards. Both UL and IEC ratings can appear on a datasheet with differing values. Different geographic regions require or follow different standards. It is for this reason that both these global standard ratings are mentioned on the datasheets. When choosing a terminal block, you should be aware of your project’s overall safety standards and ensure that the terminal block ratings comply from a performance and sustained usage basis.

Along with safety ratings there are some other terminal block aspects which need to be considered while selecting the right terminal block. These include optimal operating / service / ambient temperatures, housing material utilised, degree of pollution, grade of the housing material and the specific area of application. As you can see, there is no one-size-fits-all scenario or best over all the rest when selecting a terminal block. However, by keeping in mind the significant selection parameters, you can choose the terminal block that most appropriately fits your design, enabling your applications and performing to the standards you require. In effect, selecting the right terminal block ensures that your project wiring cycles and operational qualification times are as efficient and optimised as you required them to be.

For more detailed guidance on selecting a Terminal Block that suits your specific automation project’s needs, contact us.