crew clamps use a screw to tighten the wire and make an electrical connection and are the classic, industry standard termination method. This type can accommodate a very wide range of wire sizes and provides a reliable connection.
Spring clamps use the force of a spring to retain wire clamping. They represent a newer alternative to screw clamps and are particularly useful in applications using small wire diameters and limited working space.
Insulation displacement connections (IDC) push the wire between two sharp pieces of metal, allowing a connection to be made without exposing any bare wire.
Tab connections are designed to be inserted and removed rapidly without the need for soldering. They are also known as spade or blade terminals.
Orientation
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.
Features
Terminal blocks may include one or several special features.
The wire connections on pluggable terminal blocks allow for the circuit to be broken without any unwiring, enabling quick disconnection, testing, and maintenance. Pluggable terminal blocks can often be combined in such a manner that removing a single plug disconnects power to the entire group of terminals at once.
Stackable terminal blocks can be mounted next to each other to save space; they are typically
DIN Rail mounted devices.
The product may feature an indicator light, typically a light-emitting diode (LED), to verify that current is flowing through the device.
Some terminal blocks feature a diode between circuits to allow lamp testing and provide reverse polarity protection.
