Underground conduit serves as a vital protective pathway for electrical wiring and cables. Its primary purpose is to safeguard the enclosed conductors from a wide range of hazards found beneath the ground. This includes physical damage from external forces like accidental digging or soil pressure, as well as environmental factors such as moisture, corrosive soil chemicals, and insects. By encasing cables in a durable conduit, installers ensure the long-term safety, reliability, and service life of the electrical system.

Conduit also provides flexibility for future upgrades or repairs. Instead of re-excavating the entire trench to replace a damaged cable, a new cable can simply be pulled through the existing conduit, a process that is much faster and more cost-effective.

The choice of conduit material is a critical design decision based on the project's specific requirements, cost, and environmental conditions. The most common types include:

• Rigid Metal Conduit (RMC): Made of heavy-duty galvanized steel, RMC is the most durable option and is used in applications where maximum physical protection is required, such as under roadways or in areas with heavy vehicle traffic.

• PVC Conduit: This non-metallic conduit is lightweight, easy to handle, and resistant to corrosion and chemicals. It is the most widely used type for general-purpose underground installations. We offer a full range of tools for cutting, bending, and joining PVC conduit.

• HDPE Conduit (High-Density Polyethylene): A flexible, plastic conduit known for its toughness and resistance to moisture and abrasion. Its flexibility makes it an excellent choice for complex installations and horizontal directional drilling, where traditional rigid conduits cannot be used.

A professional conduit installation requires meticulous attention to detail and a systematic approach to ensure safety and compliance.

1. Planning and Trenching: First, a detailed route is planned and marked, making sure to identify all existing utilities by contacting local services. The trench is then excavated to the required depth, which varies depending on the type of conduit and local electrical codes.

2. Laying and Joining: The conduit is laid in the trench and assembled. For PVC, sections are joined using solvent cement to create a permanent, watertight seal. For metallic conduit, threaded or compression fittings are used.

3. Backfilling and Compaction: Once the conduit is laid and has passed inspection, the trench is backfilled and compacted in layers to ensure stability and prevent the ground from settling later on.

A professional underground cable installation project is a systematic process with distinct phases. We categorize the process into three main stages:

1. Preparation Phase: This involves all the work done before a single foot of cable is laid. It includes a thorough site survey and route planning, which is essential for identifying all existing underground utilities. This phase also includes securing all necessary permits and preparing the site by digging trenches or initiating horizontal directional drilling. The right tools for this phase ensure the cable path is clear and safe.

2. Installation Phase: This is the core on-site work. It involves the use of specialized equipment to safely and efficiently pull the cable through trenches or conduits. This includes setting up hydraulic drum stands to unspool the cable, using a duct rodder to feed a pulling rope, and operating a hydraulic cable puller to apply the precise, controlled tension needed to move the cable without damage.

3. Restoration and Commissioning Phase: Once the cable is successfully installed, the trench is backfilled and compacted to prevent future ground settling. Warning tape is often placed as a final safety measure. Before the system goes live, thorough testing and commissioning are performed to verify the integrity of the insulation and ensure the entire system is ready to carry its electrical load.

The cable pulling phase is the most critical and tool-intensive part of the installation. Using the right equipment is non-negotiable for protecting the high-value cable and ensuring worker safety.

• Hydraulic Pullers and Winches: The workhorses of the installation. Our pullers are equipped with real-time tension monitoring to prevent over-tensioning that could damage the cable. The constant pull they provide is far superior to manual labor and is essential for long, complex pulls.

• Duct Rodders: These flexible, high-tensile fiberglass rods are used to push a pulling rope through long and complex underground conduits.

• Cable Rollers and Sheaves: These are used at intervals in the trench and at all bends to support the cable and significantly reduce friction during the pull. This protects the outer sheath from abrasion.

• Cable Grips and Swivels: The connection between the pulling rope and the cable. A mesh cable grip distributes the pulling force evenly, while an anti-twisting swivel allows the rope to twist without transferring the torque to the cable, preventing damage and kinking.

• Drum Stands and Trailers: For heavy reels, a hydraulic drum stand or trailer is necessary to safely lift the drum and control its rotation during the pull, ensuring a smooth, continuous feed of the cable.

High-voltage (HV) underground cable installation is governed by stringent international standards to ensure safety, reliability, and long-term performance. While specific local codes may apply, the primary global standards are provided by the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE). Key standards include:

• IEC 60840: This standard covers power cables with extruded insulation and their accessories for rated voltages from 30 kV to 150 kV. It specifies the test methods and requirements that the entire cable system must pass.

• IEC 62067: This is for even higher voltages, from 150 kV to 500 kV, and sets the test methods and requirements for these extra-high-voltage cable systems.

• IEEE 400 Series: The IEEE standards provide comprehensive guides for field testing of shielded power cable systems. For example, IEEE 400.2 outlines the use of Very Low Frequency (VLF) testing, which is a common method for verifying the integrity of newly installed cables.

• National Electrical Code (NEC): While primarily a U.S. standard, the NEC's articles on trenching depth, conduit fill, and proper spacing for heat dissipation are widely respected and often referenced globally.

The proper installation of high-voltage cables is a non-negotiable factor for the safety and longevity of the entire electrical grid. Unlike lower-voltage cables, HV cables operate at extreme electrical stress levels. Any flaw, no matter how small, can lead to a catastrophic failure. The standards address critical parameters that, if not followed, can lead to:

• Insulation Failure: Improper bending, excessive pulling tension, or mechanical damage during installation can create micro-fractures in the insulation. Over time, these weak points can lead to insulation breakdown.

• Overheating: HV cables generate significant heat. Standards specify minimum trench depths, spacing between cables, and the use of thermally-stable backfill (e.g., thermal sand) to ensure heat is properly dissipated. Overheating can accelerate insulation degradation and cause cable failure.

• Water Ingress: Even a tiny breach in the outer sheath can allow moisture to enter the cable, leading to a phenomenon called "water treeing" that progressively degrades the insulation. Standards mandate the use of watertight joints and proper terminations to prevent this.

Professional-grade equipment is essential for adhering to high-voltage cable installation standards. Our tools are engineered to eliminate common installation errors and protect the cable at every step.

• Tension-Controlled Pullers: Our hydraulic cable pullers are equipped with dynamometers to ensure the pulling force never exceeds the manufacturer's specified maximum pulling tension, protecting the cable's conductors and insulation from stretching and damage.

• Precision Tools: Specialized stripping and crimping tools are used to prepare the cable ends for terminations and splices. They ensure a clean cut and a perfect fit, which is crucial for preventing electrical stress points and moisture ingress—the two main causes of failure at connection points.

• Reel Handling Equipment: For the massive and heavy drums of HV cable, our hydraulic drum stands and trailers provide a safe and controlled way to unspool the cable, preventing kinking or damage from free-rolling reels.

A duct rodder is a long, flexible rod, typically made of fiberglass, that is wound on a reel. Its main function is to feed a pulling line or a rope through a conduit that is already in place. The rodder's stiffness allows it to be pushed over long distances and around bends without bunching up. Once the rodder reaches the other end of the conduit, the pulling line is attached to it, and the rodder is reeled back, pulling the line through.

A swivel is a critical component in a cable pulling setup. It's a rotating device placed between the pulling rope and the cable grip. The purpose of the swivel is to prevent the pulling rope's rotation from being transferred to the cable. As a hydraulic puller winds the rope, the rope naturally wants to twist. The swivel allows this twisting to occur freely, preventing the cable from coiling, kinking, or being damaged during the pull.

The machines used for underground cable installation can be divided into two main categories based on their function: machines that prepare the path, and machines that install the cable.

1. Trenching and Laying Machines: These machines are used to prepare the ground for the cable. This category includes:

   • Trenchers: Machines that use a digging chain or wheel to excavate a narrow, continuous trench for the cable or conduit.

   • Vibratory Plows: These machines create a slit in the ground and simultaneously feed the cable into it without the need for a wide, open trench. This "ditchless" method is faster and less disruptive.

   • Horizontal Directional Drilling (HDD) Rigs: For complex installations under roads, rivers, or existing structures, these rigs drill a pilot hole and then ream it out to accommodate the cable or conduit.

2. Cable Installation Machines: These are the machines that handle the cable itself, from the reel to the final position. Our product line focuses on these specialized machines.

Ningbo Changshi Electric Power Machinery Manufacturing Limited specializes in the machines and tools for the cable installation phase. Our range of equipment is designed to make the process safe, efficient, and precise.

• Hydraulic Cable Pullers and Winches: These are the most crucial machines for the cable pulling process. They provide a constant, controlled pulling force to draw the cable through a conduit or trench over long distances. Our models are equipped with real-time tension monitoring systems to prevent over-tensioning, which could damage the cable's conductors or insulation.

• Cable Drum Stands and Trailers: For heavy cable reels, our hydraulic drum stands and trailers provide a safe and stable way to lift and unspool the cable. They are essential for a smooth, continuous feed and prevent the cable from kinking. Our trailers also provide a secure way to transport drums to and from the job site.

• Cable Conveyors: These machines assist in pushing the cable through a conduit, working in conjunction with a hydraulic puller. They are particularly useful for long pulls or in sections with multiple bends, as they reduce the overall tension required, protecting the cable and prolonging the life of the pulling machine.

Fiber optic cable installation is governed by a set of technical guidelines that focus on preserving the cable's optical integrity. Some of the most widely referenced standards and guidelines include:

• Maximum Pulling Tension: Unlike power cables, which are pulled with kilonewtons of force, most fiber optic cables have a maximum installation pulling tension of around 2,700 Newtons (600 pounds) for outdoor cables. Our hydraulic cable pullers are equipped with tension monitoring systems to ensure this limit is never exceeded.

• Minimum Bend Radius: This is a critical factor. The standard is typically 20 times the cable's outside diameter during a pull (dynamic) and 10 times the outside diameter when stationary (static). Bending the cable too tightly can cause microbends in the fiber, leading to signal loss. Our cable rollers and sheaves are designed to provide a smooth, controlled path that respects these bend radius limits.

• Telcordia GR-20-CORE: This is a comprehensive industry standard in North America for qualifying the performance and reliability of outside plant (OSP) optical fibers and cables. Adherence to this standard ensures the cable can withstand the rigors of installation and a long service life.

Using the right equipment is the only way to meet these strict standards and ensure a successful installation. Our equipment is specifically designed to address the unique challenges of fiber optic cable.

• Tension-Controlled Pullers: Our hydraulic pullers are not just for power cables. They are precisely calibrated to apply the gentle, steady force needed for fiber optic cables, with a dynamometer to provide real-time feedback and a fail-safe against over-tensioning.

• Duct Rodders: For installations in conduit, our duct rodders are essential for feeding the pulling line through long, convoluted paths without pushing on or damaging the cable itself.

• Cable Swivels and Grips: A fiber optic pulling swivel is critical. It allows the pulling rope to twist freely without transferring that torque to the cable, preventing damage and kinking. The specialized mesh pulling grip distributes the pulling force evenly, protecting the delicate internal fibers.

By using professional-grade tools, you ensure that the cable is not just installed, but installed correctly, preserving its performance and warranty.

A professional underground fiber optic cable installation is a multi-phase process that requires meticulous planning and the use of specialized tools to protect the delicate fiber.

1. Site Survey and Planning: This is the most crucial phase. It involves a thorough site assessment to determine the best route, identify existing underground utilities to prevent damage, and calculate the pulling tension and bend radius requirements for the specific cable being used.

2. Trenching or Conduit Laying: A trench is excavated along the planned route. For most fiber optic installations, a conduit is laid inside the trench. This conduit acts as a protective pathway for the cable, shielding it from moisture, chemicals, and mechanical damage. It also makes future repairs or upgrades much easier.

3. Cable Pulling or Blowing: This is the core installation step. There are two primary methods:

   • Pulling: The most common method involves a pulling rope and a hydraulic cable puller. The rope is fed through the conduit using a duct rodder. The cable is then attached to the rope with a special swivel and pulling grip and is pulled through the conduit.

   • Blowing: A more advanced method uses a fiber blowing machine and compressed air to push the fiber optic cable through the duct. This technique is often used for long distances and complex routes with many bends, as it creates less friction and stress on the cable.

4. Splicing and Termination: Once the cable is in place, the individual fibers are connected to other cables or equipment. This is done through splicing, a process of fusing two fibers together with a machine, or termination, which involves installing a connector on the end of the fiber. This phase is critical for ensuring the signal's integrity and minimizing attenuation (signal loss).

5. Testing and Commissioning: After installation, the cable is tested using tools like an Optical Time-Domain Reflectometer (OTDR) to verify its performance. This test confirms that the cable was not damaged during the installation process and that signal loss is within acceptable limits.

The choice between pulling and blowing depends on the project's specifics, but both methods have a place in the industry.

• Cable Pulling is a traditional, well-understood method that uses physical force to draw the cable through the conduit. It's highly effective for many projects and our hydraulic cable pullers provide a controlled, safe way to execute the pull without exceeding tension limits.

• Cable Blowing is a modern technique that uses high-pressure compressed air to push the cable into the duct. The air creates a cushion that reduces friction, allowing for much longer installation runs without the risk of over-stressing the cable. This method is often preferred for long distances or for installing lightweight microduct cables.

Our company provides a full range of equipment for both methods, from hydraulic pullers with tension monitors to specialized duct rodders and accessories, ensuring a perfect fit for any project's needs.

Controlling pulling tension is one of the most critical aspects of high-voltage (HV) cable installation. Exceeding the manufacturer's specified maximum pulling tension can stretch the conductors and damage the sensitive insulation, leading to premature cable failure. To meet these stringent standards, installers must use specialized equipment.

Our hydraulic cable pullers are designed with an integrated dynamometer and a tension monitoring system. This allows the operator to set a maximum pulling limit. If the tension approaches this limit, the machine automatically slows down or stops, preventing damage. This technology is essential for demonstrating compliance with HV cable installation standards and for protecting the valuable asset being installed.

The minimum bending radius is a critical standard for HV cables, which are stiff and unforgiving. Bending the cable too tightly can cause the insulation to crack or lead to a phenomenon known as "stress concentration," which can cause electrical failure. The dynamic (during installation) bending radius is typically much larger than the static (once in place) radius.

To maintain the correct bend radius, our professional installation teams use specialized cable rollers and sheaves. These rollers are placed at bends in the trench or conduit to guide the cable smoothly and prevent it from being forced into a tight turn. They significantly reduce friction and ensure the cable adheres to the manufacturer's specifications throughout the entire pull, thereby meeting installation standards.