When you have a set of electrical wires to connect, a terminal block provides a safe, convenient way to keep them organized. They are rugged, easy to use and designed to keep wires of varying gauges securely connected.
A terminal block is a set of two or more similar screw-down connection points. You can connect wires at these points. A terminal strip combines many similar blocks in a single device. In a strip, the blocks are insulated from one another.
A terminal block’s main functions are to connect and to insulate. The main block body is made of a tough material, such as plastic or ceramic, that electrically isolates adjacent blocks. The conducting parts are made of copper and corrosion-resistant metals compatible with copper.
A terminal block must first be mounted in a safe, stable location away from moisture. To use it, strip about ½ inch of insulation from the two wires you want to connect. You then insert the bare wires into the block’s metal connectors and screw them down until they’re securely fastened.
While most terminal blocks simply create an electrical connection, some have built-in fuse holders, indicator lamps or other features that add functionality for more sophisticated applications.
You can find dozens of types of terminal blocks, some generic, some specialized. Designers have developed terminal blocks for household, industrial, electronic and many other uses.
You can use a terminal block to organize wires having different functions. Many terminal blocks have a labeling scheme that lets you identify how the wires are organized.
Terminal blocks are commonly available with one of three different wire entry angles: 45°, 90°, or 180°. 90° and 180° types are also referred to as horizontal and vertical, respectively.
Contact and Wire Specifications
When discussing terminal blocks, the term “contact”, also known as a position, way, or pole, refers to a wire attached to the block. The number of contacts is an important specification when considering a product, as a buyer is required to match this number with the number of wires necessary for a project or application. Contact pitch refers to the distance between each contact, measuring from the center of each hole or opening. Contact pitch is directly related to the number of contacts and is typically expressed in millimeters (mm).
Terminal blocks are typically manufactured to accept a range of wire or conductor sizes. North American wire size is expressed in American wire gauge (AWG), which is a standard for non-ferrous wire conductor sizes. Higher AWG numbers represent smaller conductor diameters, and vice versa. For example, a typical AWG 12 household wire has a larger diameter than a AWG 22 telephone wire.