Types of Terminal Blocks Explained With All Accessories
There are lots of terminal block types available in the electrical market. I personally used all of them in my professional life and experienced their usage areas. Before listing their types I want to define what a terminal block is.
The terminal block is a type of connector used to connect two or more cables to each other. By using a terminal block it is possible to make a safe connection between the cables. Using a terminal block is the most effective way of preventing incorrect wiring.
Using a terminal block has many advantages for the users. Because it is cost-friendly compared to other connector options. It can be installed easily. It doesn’t require too much maintenance and troubleshooting. It saves space in electrical installations. It has a finger-safe connection to prevent electrical shock. It can be used with or without ferrules.
Terminal Block Types
Terminal blocks are commonly used in industrial and power management applications. Below you can see the most popular types of terminal blocks.
1. Feed-through terminal block
The feed-through terminal block is used for connecting conductors and can have one or more connection levels that are insulated against one another. Grey is the color of the phase, blue is the color of the neutral blocks.
2. Ground terminal block
The ground terminal block is used to mechanically and electrically connect wires to the DIN rail. Thus allowing the rail to function as a ground busbar. The colors of the ground block are green and yellow.
3. Multi-level/Sensor terminal block
A double-level terminal block offers twice the wiring density of feed-through blocks. Triple-level block enables either high-density wiring or simplified, low-cost sensor wiring. They are used to save space in the installation.
4. Fuse holder terminal block
The fuse block provides fuse protection for PLC output devices or modules. It is used for safety purposes and you can easily replace the fuse after its operation.
5. Disconnect terminal block
Disconnect terminal block is an easy solution to enable circuits to be opened to perform tests while the system is powered. Test operations can be performed easily by using disconnect blocks.
6. Mini terminal block
The mini terminal block is used in applications where panel space is at a premium. The depth of this terminal block is small and it can fit any application.
7. PCB terminal block
PCB terminal block is used in printed circuit boards. PCB block is the smallest member of the terminal block family. It can be used on any electronic device and enables a safe connection.
Terminal Block Accessories
Terminal blocks have some accessories. By using the accessories it is possible to increase the functionality of a terminal block.
1. End stop
The end stop prevents terminal blocks and other DIN rail-mounted components from sliding along the rail. It is strong and robust.
2. End cover
The end cover is used to separate the last live open terminal in an assembly. This is a vital safety function since terminal blocks are supplied with one open side.
The separator allows visual and electrical separation of different terminal block groups. It provides the necessary electrical spacing between adjacent insulated jumpers or between exposed ends of cut jumpers.
The jumper is used to electrically interconnect two or more terminal blocks. Jumpers are available in two, three, four, and longer pole configurations. They are cuttable and made of electrolytic copper with corrosion-resistant nickel plating. Insulated jumpers reduce the risk of accidental electrical shock.
5. Marking tag
Marking tag provides system organization and efficient identification of the terminals and other components. It is available in blank or preprinted configurations and fits onto the terminal block.
6. Top cover and label holder
The top cover serves as a protective cover for uninsulated jumpers. It is available blank or printed with electrical symbols. Label holder attaches to the end stop or din rail and provides for easy identification of terminal block assemblies.
7. Test plug
Test blog is used for hands-free circuit troubleshooting and testing. It is inserted into the jumper hole of the terminal block current bar.
Terminal Block Connection Technologies
Terminal blocks have various types of connection technologies. According to the requirements of the application, the below technologies can be preferred.
1. Spring cage connection
The terminal point is opened with a standard screwdriver. All you need to do is to push the cage. After the conductor has been inserted into the clamping space, the screwdriver is removed and the conductor automatically makes contact. You can connect a wire to a terminal block just in seconds.
2. Push-in connection
With the push-in connection technology, the force on the conductor is generated by a pressure spring made of high-quality, acid-resistant stainless steel. The spring sits in a cage and is automatically opened upon connection. This is the fastest connection method because you do not need a screwdriver if you use solid conductors or conductors with wire-end ferrules.
3. Screw connection
Screw connection technology makes an electrical connection by using a screw to tighten the wire. Screw connection technology is the most cost-effective option. But it takes time to mount the wire. Besides the wire should be tightened with the right power.
Specifying a Terminal Block System
1. Select the type
Select from the many types of terminal blocks as required for your system: screw-type or screwless, feed-through, multi-level, mini, ground, fuse, disconnect, or direct mount.
2. Determine the electrical specifications
Determine your requirements for the maximum wire size, current, and voltage for each terminal block.
3. Select the accessories
Select the appropriate end cover(s) and end brackets. Then decide if you would like to use jumpers, end covers, test plugs, separators, or marking tags.
4. Calculate the rail length
Calculate the width and quantity of terminal block in your assembly to determine the total rail length.
Terminal Block Selection Parameters
When selecting a terminal block system you have to know your overall system requirements. There are different factors to consider in your design as detailed below.
1. The number of poles
The number of individual circuits is also known as the pole count. This can be as few as a single pole, and as high as 48 poles. You should identify how many individual circuits are needed in your design.
2. Size of the block
Terminal blocks are produced in different sizes. When the current capacity increases the size of the terminal block will be larger.
3. Voltage rating
The voltage rating is in part determined by the dielectric strength and pitch of the terminal block housing. You should determine the nominal and insulation voltage ratings of the system.
4. Current rating
The maximum nominal current per pole that the terminal block is intended to be used. Generally, this electrical specification is a function of the cross-sectional area. Operating at too high of a current can cause overheating and damage to the terminal block, leading to major safety concerns.
5. Wire size
The minimum and maximum wire sizes are other important factors. You have to be sure whether the wires will physically fit into the terminal block or not. Besides, the type of wire should also be considered. Stranded, single-core or multi-core wires can be connected to the blocks.
6. Ferrule usage
Wires can be mounted to terminal blocks with or without ferrule. Using ferrules may change the size of the block.
7. Torque rating
If you use a screw-type connection you have to check the torque ratings on the surface of the block. If you apply too much force, the screws and the body can be deformed.
8. Operating temperature
Operating temperature values are needed to be checked if the application is in very high or low temperatures.
9. Connection technology
Another step in selecting the right terminal block is to choose the desired connection technology. There are different connection technologies such as screw, push-in, and spring-mounted.