Guide to Terminal Block Types for Industrial Use
by Simcona on Jul 17, 2023 7:59:01 PM
When it comes to connecting electrical systems, there are DIY-grade solutions, and there are professional solutions.
Terminal blocks are the more sophisticated version of soldering or taping, offering a convenient way to connect and terminate wires.
There are many ways to classify terminal blocks; the most common ones are connection method and wire-securing method. By understanding how each type works, you can ensure safe connections, make maintenance and troubleshooting easier, and streamline the overall assembly.
Let’s run through each terminal block type you might come across in industrial projects so you’re prepared to design or source wisely.
- By Connection Type
- By Securing Method
- By Function
- Other Types
What to Expect in Any Terminal Block
Sure, you could splice or tape twisted wires together, but what if you have several wires that need joined nearby? Or several outgoing wires that need to connect to a single incoming wire?
In many electrical and electronic applications (like control panels), terminal blocks are a must for neat layout and quick identification.
All connection blocks have an insulating body that houses a current-carrying bar or strip and provides a base for the clamp. The blocks usually receive power carried via wire conductor from a larger source.
The most common mounting solution for terminals is DIN rail, as it tends to simplify wiring setup and save space in the panel or cabinet.
As for the specifics of choosing terminal blocks, it’ll depend on whether you’re using them for power distribution, control, or another function in the assembly.
Different products have different:
- Voltage ratings
- Current ratings
- Wire size/type
- Pole count
Terminal Block Styles by Connection Type
Easy to spot all over North America, barrier (aka single-row) terminal blocks consist of a plastic or thermoplastic body with multiple terminals separated by barriers. Terminals can use either a screw or clamp to secure wires (more on that later). Barrier terminals sometimes include a small lid or enclosure to protect the cabling.
Barrier terminal blocks provide individual wire termination points, allowing independent connections for each wire. As such, common uses include:
- Power distribution
- Industrial control systems where circuit isolation is a must
- Vibratory environments
- Domestic wiring
- Other high-voltage environments
IEC PCB Mount
IEC PCB (printed circuit board) mount terminal blocks, aka Euro style or wire-to-board blocks, originated from IEC assemblies. These components work by placing bare wires in the module, where housing and a clamp secures the wire. IEC-style blocks are typically short PCB solder connections.
PCB terminal blocks can be single-, dual-, or multi-level structures (with the latter usually containing three or four levels). Pay attention when specifying PCB terminal blocks, as they come with one of two mounting options:
- Integral pins for mounting through the board (These types are also called electronic blocks)
- Pluggable pin strip mounting
Feed-through terminal blocks are at their best when they create multiple wire-to-wire connections. By managing a large amount of wiring, they conserve space and better organize the assembly.
This terminal block type features two input sides (one on each side) where two distinct wires are fed through the housing. They use the screw-in method of connection, coming with predrilled holes for securing them into place.
Like their PCB mount cousins, feed-through blocks come in single, dual, or multilevel modules.
This type of terminal block works by accepting a circuit board edge into its housing. Putting them together matches the copper traces and screws the block into an enclosure. There’s no soldering necessary with this block type.
Some electromechanical designers swear by this block type because of their low cost of ownership. Since the circuit board itself serves as the male part of the connection, edge connectors require only one discrete female connector. Edge connectors are also pretty durable relative to their initial price.
Edge connectors are common in:
- Expansion slots on computers for peripheral cards
- Your old Nintendo game cartridges!
Terminal Block Types by Securing Method
You’ve probably already noticed a few different ways terminals can secure the wires they’re charged with protecting. There are others too – in fact, some buyers and manufacturers categorize terminal blocks by securing method rather than the buckets listed above.
Because there are several wire-securing systems, and some have an annoying number of alternate names, let’s walk through these categories as well:
This is the most common way to secure electrical wires in a device.
These terminals consist of a metal or thermoplastic body with a clamping mechanism that secures wires using screws. This design enables a reliable connection by tightening the screws, which compresses the wire against a metal contact within the block.
These terminal blocks accommodate a wide range of wire sizes and are suitable for commercial and domestic wiring carrying moderate electrical currents.
There’s also a physical aspect to their application: They can handle the physical stress of mounting multiple wires up to 250 kcmil each in the same area. Screw terminals are made of steel and other strong materials so they can support connection of heavy wires.
You may know the spring-cage connection terminal block by one of its million or so alternate names:
Spring terminals work similarly to terminals that rely on screws. However, instead of tightening a screw to connect a piece of wire, a preloaded spring clamps pieces of metal together.
Most of these terminal blocks require the user to attach the wire to a ferrule via spring release before insertion. Some spring-clamp terminal blocks require a small screwdriver for attachment, though a specific torque isn’t necessary.
One reason spring-cage terminal blocks are popular is that they require less skill to use. They offer savings on assembly time, on top of having a reasonable sticker price. However, the connections are less secure than those using screws.
Common uses include:
- Small wires (they work particularly well here)
- Vibration-heavy environments
- Industries where wiring changes are frequent
- Controller interconnection in small spaces
As if spring-cage connectors weren’t confusing enough, meet another close relative(s)! Push-in terminal blocks are non-ferrous metal components that come with their own set of alternate names:
- Push button
Push-in terminal blocks also allow for a simple connection and fast installation. The user simply inserts the conductor into the clamping unit.
Just like spring-loaded types, push-in terminal blocks work best when the connecting wire has a ferrule. Where these terminal block types are different is the release method – push-fit release devices are attached right next to the wire insertion spot.
Popular use cases include:
- When you need 600 V capacity, but also a thin design
- Marine environments
- Chemical plants
- Applications with frequent changes – you can release the conductor tool-free
Insulation-displacement connector terminal blocks are also called IPCs (insulation-piercing contact). IDC terminal blocks are common in applications that call for mass termination:
- Networking equipment
- High-density wire termination
This unusual technique involves mechanically forcing unstripped, unprepared wires into slots inside the block. The assembler then adds pressure, causing sharp metal contacts to pierce the insulation and create electrical contact.
Engineers use IDC terminal blocks as a cost-efficient means of making a high number of contacts. Installation is quick and eliminates the need for a separate wire-stripping operation.
This terminal block type was once a subpar fit for stranded wire, but nowadays you’ll find manufacturers offering IDCs for both solid and stranded wire.
Terminal Block Types by Function
There are many key electronic components that go hand-in-hand with terminal block use. They serve similar functions in:
- VFDs (variable frequency drives)
- PLCs (programmable logic controllers)
- I/O (input/output) blocks
Let’s look at some other special cases where the setup may look a little different.
Ground terminal blocks operate much like a screw terminal. However, instead of connecting wire-to-wire, the terminal connects an incoming wire to solid ground.
The wire terminates at the mounting location of the block. For example, in DIN-mounted ground blocks, the rail acts as a busbar and distributes ground potential to other ground terminals on that rail.
These connection terminals are widely available in single-, double-, and three-level format at vendors like Weidmüller.
Fused-connection terminal blocks put overcurrent protection in-series, between the wire-in and wire-out spaces. This eliminates the need for external fuses, adding flexibility to your layout and current level.
Naturally, this type is ideal for designs that specifically need fuses for overcurrent protection. Certain versions are built for use in potentially explosive areas.
Multilevel versions are also available. Some manufacturers have even created variants with indicator lights so users can see the fuse’s condition.
Thermocouple lead connections aren’t compatible with your everyday terminal blocks. Instead, they use special thermocouple blocks.
If a metal thermocouple wire touches a dissimilar conducting material inside a standard block, it creates unwelcome voltage. Thermocouple terminal block designers have come up with two options for avoiding that hazard:
- Eliminating the metal connection strip, instead clamping leads together on both sides of the block
- Using a connection strip, but matching its metal type to the wire’s
Power distribution terminal blocks are notable for their need to carry high current levels. Even more so than other connection types, their primary goal is safety.
These blocks come in various sizes and materials to suit your application. No matter the type, they come with heavy-duty contacts that can withstand long-term vibration or load surges.
Molded Case Circuit Breaker
Molded case circuit breaker (MCCB) terminal blocks have a unique design, featuring two separate terminals that facilitate contact from either side of the block.
These terminal blocks are also safety-first, but are specific to MCCB applications. They improve contact resistance between circuits and reduce risk of electric shock or fire in:
- Control panels
- Bus duct plug-in units
- Other industrial & commercial environments
Other Types of Terminal Blocks
Yes, there are even more ways designers, manufacturers, and purchasers sort out terminal blocks. Consider the value these features could bring to your assembly:
Most terminal connections involve the wire going directly into the housing. Pluggable terminal blocks are the exception.
While they still include wires inserted into a housing, pluggable blocks add the benefit of modular housing you can insert directly into a circuit board. They use a plug and receptacle to form a quick connection.
Plug-in terminal blocks are valuable in cases that might require hot-swapping. Along these lines, they add convenience to assemblies that need frequent disconnection, as they keep users from having to disconnect wires individually.
Various Wire Orientations
Industrial terminal blocks are available in three common wire-entry orientations:
- Horizontal (90°)
- Vertical (180°)
The physical dimensions of your overall design often determine which wire orientation – and terminal block – you should choose.
How to Select a Terminal Block?
In most industrial electrical assemblies, terminal blocks are an upgrade over sloppy solutions like tape and twisting. Terminal connections look professional and perform like a professional.
As you’re specifying them for your next projects, be careful. There are many types, and many more names. Some have the same characteristics, while others will give you very different results.
The top factors to watch for are:
- Current & voltage ratings
- Number of circuits needed (indicates the # of poles the block will need)
- Environmental performance
- Futureproofing (ex.: screw connections are easier to modify)
- Do they come from the same manufacturer (likely the only factor your engineers care about)
Watch out for a future blog post on choosing the correct terminal block from a distributor based on your application. For now, check out our current resources (get it?) or, if you’re ready to buy, browse a manufacturer list:
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