What are Anchor Clamps?
Anchor clamps are essential components in the electrical industry. They are fittings used to fix the ends of conductors and bear the tension of conductors, called anchor clamps, also known as fastening fittings or anchoring clamps (collectively referred to as "anchor clamps"). Among them, anchor clamps used to fix guy wires on towers are called guy wire fittings. These cable anchor clamps play a critical role in securing electrical conductors in various applications.
Types of Anchor Clamps
Anchor clamps are classified into bolt type, compression type, wedge type, and preformed armor rod type according to structure and installation method:
Bolt type anchor clamps are anchor clamps that use bolts to fix conductors.
Compression type anchor clamps are anchor clamps that fix conductors by compression method.
Wedge type anchor clamps are anchor clamps that use wedges to fix conductors, also known as wedge tension anchor clamps.
Preformed armor rod type anchor clamps involve wrapping preformed helical strips around conductors or ground wires to bear mechanical or electrical loads.
In addition, anchor clamps are divided into two major categories according to whether current flows through the clamp after installation or not:
When current does not flow through the clamp but flows through the conductor itself, they are mostly clamps fastened by bolts, called bolt type anchor clamps. Their physical objects and installation scenes are shown in Figure.
When current flows through the clamp, they are mostly clamps fastened by compression method, called compression type anchor clamps. Their physical objects and installation scenes are shown in Figure.
Advantages of Using Anchor Clamps
Enhanced Structural Stability and Safety: Made of high-strength materials, corrosion-resistant, weather-resistant, with high tensile strength, they can effectively bear horizontal and vertical forces, including wind loads, seismic loads, and conductor tension.
Fast Installation: Compared to other fixing methods, they are faster and more convenient, requiring less time and effort. No waiting time for curing is needed. They can immediately bear loads after installation, making them more suitable for rapid construction scenarios compared to chemical anchors. Hold down anchor clamps provide secure fastening immediately upon installation.
Multifunctional Application and Compatibility: Can be used to fix power conductors, lightning protection wires, guy wires, and are also suitable for scenarios such as geotechnical anchoring and bridge reinforcement. Specialized variants include ADSS anchor clamps for ADSS cables, anchor clamps for ABC cable (Aerial Bundled Cables), and anchoring clamps for aerial bundled cables in distribution networks.
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Technical Requirements for Anchor Clamps
(1) The general technical conditions for anchor clamps should comply with the provisions of GB/T 2314-2008 and be manufactured according to drawings approved by the prescribed procedures.
(2) The connection dimensions of anchor clamps should ensure compatibility with the fittings to which they are connected.
(3) Anchor clamps bearing electrical loads should not reduce the conductivity of conductors, and their electrical performance should meet the following requirements:
The resistance between the two endpoints at the conductor contact point, for compression type anchor clamps, should not be greater than the resistance of a conductor of the same length; for non-compression type anchor clamps, should not be greater than 1.1 times the resistance of a conductor of the same length.
The temperature rise at the conductor contact point should not be greater than the temperature rise of the conductor being connected.
The current-carrying capacity of anchor clamps should not be less than the current-carrying capacity of the conductor being installed.
(4)The grip strength of anchor clamps should meet the requirements of GB/T 2314-2008, and the percentage of calculated breaking force of conductors and ground wires should not be less than the provisions of Table 3-2.
Table 3-2 Percentage of Calculated Breaking Force of Conductors and Ground Wires for Anchor Clamps
|
Fitting Type |
Percentage (%) |
Fitting Type |
Percentage (%) |
|
Compression type anchor clamp |
95 |
Anchor clamp for distribution lines |
65 |
|
Preformed armor rod type anchor clamp |
95 |
Anchor clamp for insulated wires (stripped) |
65 |
|
Bolt type anchor clamp |
90 |
Anchor clamp for substations |
65 |
|
Wedge type anchor clamp |
90 |
- |
- |
(5) For the bent extension part of non-compression type anchor clamps, when in contact with conductors and ground wires bearing tension, the radius of curvature at the exit of this bent extension part should not be less than 8 times the diameter of the conductor or ground wire being installed.
(6) The internal voids of compression type anchor clamps should be minimized to prevent moisture intrusion during operation.
(7) The connection between anchor clamps and conductors/ground wires should avoid bimetallic corrosion problems between two different metals. Bonding clamps may be used in conjunction with anchor clamps to ensure proper electrical continuity.
(8) Anchor clamps should be designed such that after installation, excessive stress should not occur in the contact area between conductors/ground wires and fittings due to breeze vibration, conductor oscillation, or other factors, which would cause damage to conductors or ground wires.
(9) Anchor clamps should avoid excessive stress concentration to prevent excessive cold deformation of conductors and ground wires.
(10) The strength of the non-compressed portion of the steel anchor rod of compression type anchor clamps should not be less than 105% of the calculated breaking force of conductors and ground wires, or meet the requirements of the purchaser.
(11) The strength of bolt type anchor clamps should not be less than 105% of the calculated breaking force of conductors, or meet the requirements of the purchaser.
(12) Compression type anchor clamps should be marked on the outer surface of the tube material with the compression position and compression direction.
Maintenance and Service Life of Anchor Clamps
The maintenance of anchor clamps is crucial for their functionality and service life, directly affecting the stability and safety of the overall structure.
Maintenance Methods:
Regular Inspection: Inspect every six months or annually for external damage, corrosion, and deformation, and check whether cables are loose. Focus on connection parts, bolt tightness, and surface coating. In industrial areas or humid environments, implement proper anti-corrosion measures. For stainless steel anchor clamps, inspect for surface integrity and proper installation.
Cleaning and Lubrication: Regularly clean anchor clamps to remove dirt and substances that may cause corrosion. Apply appropriate lubricants to enhance their durability and integrity.
Service Life:
General Lifespan: The design life of hot-dip galvanized fittings is 20-30 years. In environments with corrosion, mechanical stress, and corona discharge, the lifespan will be shortened. High-quality materials such as stainless steel or aluminum alloy can extend the life by more than 5-10 years. For example, cast iron suspension clamps have a service life of 20 years.
Main Influences: High temperatures, impacts, vehicle vibrations, and acid rain all accelerate aging. Under high loads, anchoring efficiency and fatigue performance are critical; increased temperature increases the risk of slippage and failure.
FAQ
Q: What temperature effects should be considered when selecting anchor clamp materials?
A: Temperature influences anchor clamp performance through three mechanisms: thermal expansion coefficient mismatch, material strength degradation, and accelerated creep. At temperatures above 90°C, aluminum alloy clamps expand faster than steel conductors, reducing grip pressure by up to 15%. Above 150°C, aluminum begins annealing, permanently losing temper strength. Hot-dip galvanized steel maintains properties to 200°C but zinc coating degradation accelerates above 85°C. For applications near substations or industrial areas where conductor temperatures regularly exceed 75°C, stainless steel or specialized high-temperature aluminum alloys are essential to maintain the required grip strength percentages over the design life.
Q: How does preformed armor rod type differ functionally from wedge type anchor clamps?
A: Preformed armor rods are helical conductors that wrap around the main conductor, distributing tension loads over 50-100cm length while simultaneously damping aeolian vibration. They absorb cyclic bending stress through elastic deformation of individual helical strands. Wedge type clamps concentrate all gripping force within 5-10cm length through rigid mechanical compression. Preformed rods excel in high-vibration environments and spans exceeding 300m where fatigue is the primary concern. Wedge clamps are superior for dead-end applications and acute angles where maximum grip strength in minimal space is required. Both achieve 95% grip strength but through fundamentally different mechanical principles is distributed elastic grip versus concentrated friction.
Q: What inspection criteria indicate an anchor clamp has reached end-of-life before visible failure?
A: Three non-obvious indicators signal replacement is needed: First, if bolt torque values decrease by more than 20% during re-torquing (indicates thread wear or base material yielding). Second, if wedge inserts can be removed by hand without tools (self-tightening mechanism has failed). Third, if ultrasonic thickness testing shows more than 10% cross-section loss from corrosion, even if surface coating appears intact. These criteria from GB/T 2314-2008 testing protocols identify failure modes that develop internally, invisible to standard visual inspection.
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