Terminal Blocks - Connection Terminal and Screw Terminal Definitions

The insulating body houses the current carrying elements. The body insulates the wire termination to reduce heat produced when current traverses through the wires. It also supplies a base for the clamping system and other elements including switches and fuses. The body of the terminal block has specially constructed holes for easy access to the clamping screws. The body also has a mounting foot that allows the terminal block to be clipped on and off the mounting rail without experiencing deterioration. The space saving style of a typical modular block allows high-density circuits to fit in a standard control panel. A 5mm wide block can deliver up to 60 terminations per linear foot. Standard 6mm single level blocks produce up to 50 terminations per linear foot; double level blocks can manage up to 100 terminations per foot.

The current carrying parts consist of a current bar and a clamping device. The current bar, at the core of the insulating body, is constructed from copper or brass. The clamping device fastens the wire in the terminal block and creates a dependable electric connection between the wire and the current carrying bar. The dimension of these current carrying parts varies in regard to the amperage/wire size and the construction of the block itself. Depending upon terminal block layout, wires can be clamped in position using screws, a combination of screws and pressure plates, wire cages or spring clamps. A screw is the easiest method of connection: A screw is utilized to secure the wire against the current bar. With screws and a pressure plate, the wire is constrained with a metallic plate, which fastens the wire when the screw is secured. With a wire cage, when the screw is tightened, a cage pulls upward and squeezes the conductor against the current bar. The large contact area provides exceptional contact properties. Because the screw does not have immediate contact with the conductor, wire damage is prevented. Even thin stranded wire can be connected without the use of additional Ferrules or wire pins. Spring clamps require a tool to open. The clamp encloses the wire to provide dynamic clamping. This extra holding action endures vibration.

Choosing the correct terminal block is straightforward. Just follow the steps below:

1. Determine current, voltage and wire size (AWG) to be used for the individual wire runs in the control or power distribution application.
2. Define any special space constraints imposed by the application
3. Considering the first two steps, select the appropriate rated feed-through terminal types to satisfy the electrical and space requirements. Select block widths. Double to block level and wire size if necessary to meet space requirements.
4. Determine how many blocks (number of Poles) are needed, whether any blocks need to be jumped and how the jumper connections should be made (which place).
5. Select special function block (ground, disconnect, fuse, indicating types, switch) based upon application requirements.
6. At the end of each terminal block assembly, wherever a change in terminal block size occurs or when a side of a terminal block is not used, specify as end plate. Unused sides of terminal blocks must not be left uncovered and exposed.
7. Determine where isolation partitions are needed to provide visual separation or to contain creepage within the terminal assembly. To ensure safety, isolation partitions separate blocks with different amperage ratings or voltages to prevent current/voltage jumping from one to another. Partitions also indicate to maintenance crew or electricians that there may be a different voltage in each of the groupings of blocks.
8. For rail mounted blocks, select the type of rail mounting. Calculate the length required by totaling the individual widths (thicknesses) of the terminal blocks, end plates, isolation partitions and end stops.
9. Mark wire terminations using marking tags.