A Complete Guide to DIN Rail Terminal Blocks

What exactly are terminal blocks? These insulated attachments protect electrical equipment, preventing short circuits and excess current from surging across connecting wires.

They are clipped onto DIN rails - globally standardised metal rails used to mount electrical relays, circuit breakers and similar equipment in racks, control cabinets and enclosures. DIN rails are specifically made to provide a location for control devices. In addition to terminal blocks, these might include actuators (to switch devices on), power supply units, and circuit breakers.

DIN rail terminal blocks are made from plastic or other insulating materials. They provide a safe interface between different components on and sections of the DIN rail.

DIN is an acronym for Deutsche Institut für Normung, the German Institute for Standardisation. Rack mounts - cabinets used to house industrial, communications and computer equipment - were first devised in Germany in the 1920s and the resulting standards were then globally adopted from the 1950s onwards.

Terminal blocks are also known as terminal strips or connection blocks.

Now for the crucial question - what is a terminal block used for? They allow electricians and engineers to connect the wiring from assembled equipment to the input-output ports on other equipment, creating a complete circuit.

DIN rail terminal blocks are an important component of electrical cabinets and industrial racks (assemblies), helping to protect and connect complex equipment. They have become a standard component in electrical systems used across industry. Examples include:

• Telecommunications equipment
• Building management systems (used to monitor and control the electronics within a particular building)
• Energy regulation and conservation equipment
• Air conditioning and heating systems
• Power supplies
• Lighting control systems
• Control, automation and signalling systems
• Vehicle electronics

DIN rail terminal blocks are available with a variety of specifications for different uses. Their compact size gives them a significant degree of versatility; they can be deployed even when space is limited. However, for truly small-scale work, look for miniature and even micro-miniature variations.

Some models feature one or more fuses in a special hinged section for additional protection against overcurrent, making them a good choice for use with sensitive equipment like sensors and relays. Fuses are standard components that protect against electrical surges with a component that melts when exposed to excess current, breaking the circuit. These models often feature an LED to indicate when the fuse has blown. You may see such models referred to as DIN rail fuse holder terminal blocks.

Varying current ratings are indicated by colour coding on some models.

DIN rail terminal blocks are also distinguished by their levels. A single-level model has a single wire connection - also known as a single feed through. By contrast, a dual-level model has two connections - one above the other. The second set of wiring effectively functions as a second terminal block, in more or less the same space as a single feed model. These are sometimes referred to as double density terminal blocks.

Triple and quadruple level models are also available, along with high-end eight and 16-level options.

Termination type is another frequently used classification method. Screw terminal blocks are a common, general-purpose model. These use a clamp to secure wiring, where a screw is inserted to tighten this, pressing the wire into place. In some models, the clamp is spring-loaded, providing a more secure connection resistant to vibration.

Ring terminal blocks can be deployed more quickly because they feature preinstalled nuts that are ready to be tightened without removal first. These are also known as plug-in or push-in terminals because the wires can simply be pushed into the connection gaps.

Typically smaller than standard DIN rail terminal blocks, ring terminal blocks save space. They are usually four-level models, meaning that four wires can be connected through the block.

Earth terminal blocks are a third type. Also known as ground terminal blocks, these are used with wiring that requires direct earthing (connecting to the ground to discharge excess electrical charge). They typically feature green and yellow housing and can be mounted onto DIN rails, with the wiring secured via screws or clamps.

To use a terminal block connector, it is necessary to connect it to your DIN rail. Once you have selected a fully compatible connector, clip it onto the rail and then mount it to the equipment panels or enclosures. Finally, connect the requisite wiring. DIN rail terminal blocks are specifically designed for quick and easy attachment to DIN rails.

If the placing occurs at the end of a row, you may wish to attach an endplate to the open side of the terminal block. Alternatively, a disconnected terminal block can close a row. The end block should lock to the rail to prevent sliding.

Here’s how to wire standard screw-based DIN rail terminal blocks:

1. Turn off your equipment
2. Peel back the insulation from the first inch or so of the cabling
3. Loosen the restraining screw in the entry slot on your terminal block, insert the exposed conductors, and tighten the screw back into place. Make sure it is tight - a loose screw could result in melted insulation
4. The slots may be sited on the side or the front of the terminal block. The number of slots will vary by model
5. Repeat until all cables have been attached
6. Apply the terminal block to the rail

Instead of restraining screws, your terminal block may instead have integrated clamps. To open one of these, use the included tool or something similar to depress the spring and then release the spring after the conductors have been inserted.

The process is simpler with plug-in designs:

1. Place your terminal block in the desired location
2. Attach the wiring from your equipment to the block, matching the male terminals with the female ports
3. Ensure the connections are secure

For ring terminal blocks:

1. Attach the wire to the stud by the port
2. Close the self-locking safety wing
3. Tighten the nut