The torque of terminal blocks (specifically screw-type terminals) is the most critical and direct installation parameter affecting their connection reliability. It is not an isolated value, but a key control point in a precision engineering system. The following explains the relationship between the two, from principle to practice.
Core Principle: How is torque converted into a reliable electrical connection?
The physical chain of events can be simplified as follows:
Applied torque → Generation of clamping force (axial force) → Formation of contact pressure → Determination of contact resistance → Impact on long-term reliability
Torque (T): The rotational force applied during installation using a screwdriver or wrench, typically measured in Newton-meters (N·m) or centiNewton-meters (cN·m).
Clamping force (F): The axial compressive force generated between the wire, terminal block, and conductive strip as the screw is rotated and tightened. This is the core purpose of the torque.
The relationship is influenced by several factors: F ≈ k * T / d (where k is the overall friction coefficient, and d is the nominal diameter of the screw). The friction coefficient is a key variable and is greatly affected by the threads, washers, and surface condition of the wire.
Contact pressure (P): The actual pressure generated by the clamping force at the microscopic contact points. Sufficient contact pressure can:
Break through the oxide film: The surface of the conductor (usually aluminum or copper) has an insulating oxide film; high pressure can break this film, creating metal-to-metal contact.
Increase the contact area: Cause controlled plastic deformation of the conductor, increasing the effective conductive area.
Maintain stable contact: Resist loosening caused by vibration and thermal expansion and contraction.
Contact resistance (Rc): Contact pressure directly determines the magnitude of contact resistance. There is a critical pressure above which the contact resistance tends to stabilize at a very low value; below this value, the resistance increases sharply.
Low and stable Rc means: low power loss (P_loss = I² * Rc), low heat generation, high current carrying capacity, and good signal integrity.
The torque applied to terminal blocks is not simply a matter of "tightening," but rather a precise engineering control parameter. It is the bridge that transforms mechanical energy into a stable electrical connection.
Reliability formula: Reliable connection = Correct torque × Suitable wire × Standardized process × Matching terminal design.
Core understanding: The "correctness" of the torque directly determines the "stability" of the contact resistance, which in turn is crucial for long-term electrical reliability.
Ignoring torque control is equivalent to planting a time bomb in the connection point, a fault that will inevitably trigger over time.
Therefore, in any serious industrial, energy, or transportation sector, incorporating and strictly controlling wiring torque in process specifications is an essential measure to ensure the reliability of fundamental system connections.
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