Terminal blocks are essentially secured, insulated wire connectors, but terminal block manufacturers produce them in many varieties to make wiring easier and to increase spacial efficiency. A block includes terminals that secure to wires.

Terminal types include the spring or the screw terminal block, as well as connectors like tab and insulation displacement. Terminal blocks themselves mount in various ways, including universal foot or rail as well as specific DIN-rail sizes. There are also panel mount and printed circuit board (PCB) mounts.

There are many types of terminal blocks, including the following examples listed here:

1. Single feed-through terminal blocks have one input contact and one output contact to serve wire to wire applications.

2. Dual or three-level terminal blocks have two or three sets of contacts and also come in bridged varieties which allow for connection between levels.

3. Disconnect terminal blocks permit you to easily disconnect a circuit. The two main varieties are plug, knife and sliding link.

4. Specialty terminal blocks include I/O, sensor specific, electronic circuit, PCB, thermocouple and more.

Action Steps
The best contacts and resources to help you get it done

Buy industrial terminal blocks with the correct specifications for your application

When buying terminal blocks, pay attention to voltage and current ratings. For instance, there is the standard 110 terminal block as well as the 66 terminal block for phone and other low voltage applications. Also, check to see that the connection terminals match the gauge of wire you are using, often an AWG measurement.

I recommend: AutomationDirect carries a wide range of standard DIN-rail terminal blocks and conveniently categorizes them by block type or by component type. They also carry screwless terminal blocks. Grainger is a great standby for a wide range of terminal blocks. They have a huge selection and publish specifications very clearly for easy selection.

Find PCB terminal blocks at an application-appropriate terminal block distributor

The pluggable mounting methods on terminal blocks made for printed circuit boards are much less adaptable than other mounting methods. PCB terminal blocks generally come in a smaller size range as well. Thus, you'll want to find terminal block sources that carry a wide range of PCB terminal blocks or even specialize in this type.

I recommend: Mouser Electronics carries a huge list of mini, pluggable and PCB terminal blocks. OKW Electronics sells Camden products for PCBs and the search features on their website make it easy to find terminal blocks with just the right specifications.

Find a specialty wiring terminal block

Not every manufacturer carries the full range of electrical terminal blocks. If you have a hard time finding what you are looking for at the links listed above, there are plenty of other terminal block manufacturers and sources that carry application-specific equipment.

I recommend: Tyco Electronics carries battery stud, NEMA, and Eurostyle terminal blocks as well as barrier strips, multiple tap connectors and terminal block accessories. BlockMaster Electronics carries a number of products as well, including high power, elevator style, pluggable and what they call jelly beans terminal blocks.

Tips & Tactics

Helpful advice for making the most of this Guide

• •  When matching terminal blocks to your wire, remember that AWG or gauge measurements refer to the number of times a wire passes through a wire machine. The greater number of passes, the thinner the wire. For instance, 18 gauge is smaller than 16 gauge.
• •  Sizes in excess of 4/0 measure in either CM or MCM, circular or thousand circular mils.