5AP920.1505-01 Automation panel display unit

5AP920.1505-01 Modular Terminal Blocks may be used for connection to solid core and stranded metal wires. The clamping force applied to the wire head by a screw mechanism in one of the blocks is direct and does not involve sliding or other action. However, some terminal blocks are less complex in design. The next photograph shows a pair of “isothermal” terminals designed to connect thermocouple wires.
Applying rotational force to the tip of each wire through these screws requires the use of solid wires. The strands would be abraded by the force of this combination.

However, many field instruments do not have “block” type connection points at all. 5AP920.1505-01
The 5AP920.1505-01 is equipped with pan head machine screws designed to compress the wire head directly between the screw head and the metal plate below.

Solid wires can be suitably attached to such a head connection point by partially wrapping the exposed wire end around the circumference of the screw and securing the head at the top of the wire.

The problem with crushing the wire head directly under the screw head is that the head is subjected to compression and shear forces. As a result, the top of the wire is often broken by repeated connections. In addition, the tension on the wire causes the screw to rotate, which can loosen the screw over time.

This termination technique is completely unsuitable for stranded wires because the shearing forces caused by the rotation of the screw head tend to “wear out” the individual strands.5AP920.1505-01 Direct connection to threaded connection points can be made by first pressing the compression type terminal onto the wire. The flat metal “lug” (collar) portion of the terminal is then inserted under the screw head, where it can easily withstand the shear and compression forces generated by the head.