Terminal blocks are also known as connection terminals, screw terminals, or terminal block connectors. These are modular blocks having an insulated frame, which helps in connecting two or more wires, terminating a single wire, and connecting it to a circuit or other system safely and conveniently. Terminal
blocks are very helpful in a situation where there is a need for semi-permanent connections, which may need inspections, wires replacements, repairing, and changes. Therefore, domestic wiring and industrial environment commonly use these terminals.
Furthermore, terminal blocks use a clamping component and conducting strip, which has the sole purpose of securing and organizing the connecting wires. Terminal blocks are usually modular and are mounted on a Din rail, which helps in increasing the number of terminals as per requirement.
Generally, we use terminal blocks for two purposes; First, to connect different circuits, and second, for grounding circuits. These blocks make the connection of different circuits easy and less time-consuming. And they also reduce the risk of short circuits within the system. Apart from that, terminal blocks are cheaper than other connectors and easy to work with. These are also small in size.
Terminal blocks have different cross-sectional areas ranging from 2.5 to 150 mm. The smallest PCB screw terminal block has a cross-sectional area of 2.54mm. Thus, it is very helpful for applications where high current and voltage are not very important. We use terminal blocks with a large cross-sectional area for high voltage requirements.
We can see the simplest terminal bock here.
The most common method of connection for terminal blocks is using a screw. In this method, we use a screw to tighten and secure the inserted wires. Apart from that, there are screw-less methods as well, which function just like a fish trap. In these methods when the wire is inserted the lever comes down and secures the wire. There is another method, in which we have a screw for securing the wire and a plug on the other end, which can be inserted into a female connector.
The conventional way of connecting wires like twisting them or soldering them together and wrapping them with an electrical tap for insulation is an unsafe and inconvenient method. Therefore, terminal blocks are the best replacement. Because, using terminal blocks is a much easy, better, and a flexible solution. Apart from that, the wiring modifications are much easier and safer in terminal blocks than the conventional methods. In addition, terminal blocks’ wiring is neat and organized, which makes it easy for quick identification, modification, and troubleshooting of the problem.
In the picture below we can see that it is very easy and safe to use a terminal block for connecting wires than using a conventional method.
The terminal bodies consist of a copper alloy that has the same expansion coefficient as the wire planned to use for the connection. Which prevents the losses due to the different expansion rates. It also reduces the corrosion caused by electrolytic actions between the two different metals.
Types of terminal Blocks:
There are different types of terminals blocks and each block is used in a different context but they all provide the same function of connecting electrical components in a much safer and more reliable manner. The most popular terminal block designs are as follows.
PCB mount terminal blocks:
PCB mount terminal blocks are also known as wire-to-board terminals because we can directly solder them to the PCB board. We can also configure these in single, dual, or multi-rows.
We can use these types of bocks in applications where the variation is of main concern. Apart from that, we can configure it in single, dual, or multi-rows. There are screw-down terminals where we can insert a wire and tight it with the screw.
Feed-Through Terminal blocks:
We can use these terminal blocks to create wire-to-wire connections. The configuration can be single, dual, or multi-row depending upon the requirement. In these terminals insert both wires from opposite ends to connect them.
We can also classify Terminal blocks according to their structure. There are three types of terminal blocks according to their structure; Single-feed through (basic type, used for wire-to-wire connections having one input, one output), Dual-level (Having two levels of contacts), and three-level (essentially dual-level, with an extra stacked level of contact).
Specifications to consider when selecting terminal blocks
When selecting a terminal block the most important specification to consider is its current rating. There are three specific areas that you should consider; the conductivity of the terminal block, the cross-section area, and the corresponding temperature rise. Therefore, the best approach is to select a terminal block having a current rating of at least 150% of the system’s maximum current.
Apart from that, the voltage rating should be greater than the maximum voltage of the system. Another point to consider is the pole count and pitch between the adjacent poles. In addition, we should also consider the type of wire. For single-core wires, we should use the push-in terminals and for standard or multi-core wires we should use screw terminals.
Mechanical specifications are also very important because these influence the terminal block’s footprint, orientation, and also on the accessibility of the design. Apart from that, the arrangement of blocks is also important. We can arrange the blocks in horizontal, vertical, or 45 degrees.
The picture below demonstrates the orientation of terminal blocks.
Each terminal block has its pros and cons. Therefore one should consider these pros and cons for selecting the right terminal block.