Terminal Blocks Explained

In this article, we’re going to introduce you to the Terminal Block which is an important component in any industrial setting. Terminal blocks are components with an insulated frame that has the sole purpose of securing two or more wires together.

Why use terminal blocks?

Well…. you might ask, If you want to connect wires, why not just solder them together? Or twist them together and wrap them with electrical tape?

Using terminal blocks is a much better solution for connecting wires. Terminal blocks provide more flexibility.

For example, when using terminal blocks, wiring modifications are easy because wires can be removed or added quickly.

Terminal Block wiring is neat and orderly allowing for quick identification making modification and troubleshooting easier. We’ll show you more good reasons to use terminal blocks later in this article.

Terminal block characteristics

Terminal blocks are classified based on characteristics such as structure, device type, and termination options. Let’s explore some of the classifications and characteristics of terminal blocks typically encountered in industry today.

There are a variety of methods used to connect the wires inside the terminal block. Let’s have a look at some of the more popular ones.

1) Screw-in terminal block

Probably the most commonly used method for connection is the Screw-in terminal block. Screw-in terminal blocks are those that use screws as the method for holding the wires.

Be careful! Over-tightening the screws can damage the wires and result in poor or potentially dangerous connections.

2) Barrier terminal block / Europe connectors

The Barrier terminal block is very similar to a Screw-in terminal block as they use screws to clamp the wires. Depending on the application and environment, the Barrier terminal strip may have a small lid to protect the wiring.

Like the Screw-in terminal block, it’s important to strip the wire to the correct length or the screw clamp might not make contact with the wire itself.

3) Spring-cage terminal block / Spring-loaded connection

Another common method for wire connection is the Spring-Loaded terminal block.

A connection is made by simply inserting the wires. Most of these terminal blocks require the wire to be attached to a ferrule before it is inserted.

The ferrule or wire is attached and released by inserting a spring release device. Some vendors have a unique spring release device while others require a small screwdriver.

4) Push-in / Push-fit terminal block

The Push-fit or Push-in terminal block is becoming very popular. Much like the Spring-Loaded terminal block, the “Push-fit” often requires the wire to be covered by a ferrule.

Several vendors make Push-fit terminal blocks.

A connection is made by simply inserting the wires.

The big difference between the Spring-loaded and the Push-fit terminal block is the method of wire release. Push-fit terminal blocks have the release device mounted right next to the wire insertion point.

5) IDC terminal block

Another terminal block that was first used in the Telco industry is the Insulation Displacement Connector or IDC.

The wire insulation does not need to be removed before insertion. Two sharp blades inside the terminal block will slice through the insulation and make contact with the wire.

When first introduced, this type of terminal block was more suitable for solid wire than stranded although there are vendors now making IDC’s for both.

6) Pluggable terminal block

As the name suggests, a Pluggable terminal block has a plug outlet to allow connection to a socket.

The wire is inserted and clamped with a screw. Connection to the wire is made via a plug and socket configuration. This terminal block is used in situations where a quick disconnect is required.

7) Tab Connector terminal block

On Tab Connector terminal blocks a wire attached to a connector is pushed onto a tab.  The wire can be crimp-connected or soldered depending upon the type of connector.

Tab Connector terminal blocks are also available where one side of the terminal block is a tab connection and the other side of the terminal block is a screw clamp connection.

Terminal block types

Okay…now that we have investigated some of the more common connection methods, let’s have a look at some of the different terminal block types.

1) Ground terminal block

At first glance, a Ground terminal block looks like a typical Screw-in terminal block.

Instead of connecting wires, the Ground terminal block connects the incoming wire to Ground.

The wire is terminated by the panel or the DIN Rail or wherever the block is mounted…We will talk more about DIN rails later.

2) Fuse terminal block

Fused Connection terminal blocks have a fuse inserted in series between the wire-in and the wire-out eliminating the need for external overcurrent protection.

To aid in troubleshooting, many vendors have included a built-in Fuse Failure LED circuit to provide a visual indication of the fuse condition.

3) Thermocouple terminal block

A Thermocouple block is designed to accept thermocouple lead connections. Thermocouples cannot be connected to typical terminal blocks.

As soon as the thermocouple wire makes contact with the conducting material inside the terminal block an unwanted junction occurs.

Any dissimilar metals joined together will create a new junction, and consequently an unwanted voltage.

To avoid creating a new junction, some thermocouple connectors clamp the thermocouple leads together on both sides of the block.

Some vendors have developed Thermocouple blocks with the internal metal connection strip made of the same metal as the thermocouple wire itself.

Multi-level terminal blocks

Quite often, space inside a cabinet or an electrical panel is limited. To save space, individual terminal blocks can be connected to form groups or clusters and are generally structured in multi-level configurations.

Each configuration has a different number of layers or levels. For example, a Triple level terminal block has three layers.

Terminal block schematic example

In this schematic example, the terminal blocks have 3 levels. We are only showing 4 of the several terminal blocks that create what is labeled as TB4101.

The levels are designated as B for bottom or Layer 1, M for middle or Layer 2, and T for top or Layer 3.

Interpreting this schematic is not that difficult once you know that the terminal blocks are multi-level.

The label TB4101-2M means that the wire is connected to TB4101, terminal block 2, layer 2.

Terminal blocks mounting

Terminal blocks are mounted in a variety of ways but by far the most common is by attachment to a DIN Rail.

A DIN Rail is a metal rail of a standard size universally used for mounting devices and components inside electrical panels and equipment racks.

Summary

– A terminal block is a component with an insulated frame that has the sole purpose of securing two or more wires together.

– Terminal blocks are classified based on characteristics such as structure, device type, and termination options.

– Terminal Block Connection methods include

1. Screw-in
2. Barrier / Europe connectors
3. Spring-Cage / Spring-Loaded connection
4. Push-in / Push-Fit
5. Insulation displacement / Fast connection
6. Pluggable
7. Tab

– Terminal Block Types include

1. Ground
2. Fused
3. Thermocouple

– The most common terminal Block mounting method is by attachment to a DIN Rail.

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The RealPars Team

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