Duct Cable Installation Solution

Duct cable installation refers to the process of laying and securing cables inside protective ducts or conduits. This method offers several advantages, such as enhanced cable protection, easy cable management, and future scalability. To ensure a successful duct cable installation, here's a step-by-step solution:

Installation Methods of Fiber Optic Cable into Duct

Generally, there are six approaches for optical cable installation into a duct, pulling method and air blowing method.

Pulling Method

In this method, cables are pulled through the duct manually or using mechanical pulling equipment. Pulling cables require the use of pulling grips or lubricants to reduce friction. It is suitable for shorter distances or when the duct is not obstructed.

Limitations: Optical fiber cables must be handled in compliance with their stated design ratings. Handling crews must be familiar with the cable's design ratings and the critical events during installation where design limits may be approached.

Air Blowing Method

This method involves blowing or floating cables through the duct using compressed air or special lubricants. The cables are attached to a pulling device, and compressed air or lubricant is used to push or pull them through the duct. This method is often used for longer distances and larger diameter ducts.

Limitations: Special air blowing equipment are required for air blowing method. Air blowing of fiber cable into duct systems requires continuous run of inner-duct and pressure testing for integrity. Quality of inner-duct joints is critical to the success of air blowing techniques.

Pulling Method VS Air Blowing Method: How to Choose?

Site conditions, availability of machinery and resources are crucial factors for choosing cable installation method. The differences between pulling method and air blowing method for optical fiber cable installation are shown in the table below.

Factors	Pulling Method	Air Blowing Method
Rope or not	Pulling rope pre-installed	No pulling rope to install
Power side	Equipment and manpower at two sides	Equipment and manpower at one side
Possibility of cable damage	High sidewall forces on cables and ducts may lead to cable damage.	Cable and duct can be monitored and controlled to minimize the cable damage.
Main forces	Manual pulling	Large compressor and/or hydraulic power pack
Main forces	Straight duct route	Duct route with multiple bends and undulations
Distance	Suitable for short distance (few 100 meters) installation	Preferred for long distance (over 2 km) installation

As a rule of thumb, air blowing method for fiber optic cable installation is more favored than pulling method due to improved installation efficiency, particularly in longer ducts with multiple bends and undulations and savings in manpower and installation time.

Jetting Method

The jetting method utilizes water or air pressure to propel cables through the duct. A jetting machine creates a high-pressure stream of water or air that pushes the cable along the duct. This method is commonly used in underground duct installations.

Pushing Method

The pushing method involves manually pushing cables through the duct using flexible rods or fish tapes. This method is suitable for shorter distances and smaller diameter ducts.

Pre-Installed Ducts

In some cases, pre-installed ducts are used to simplify the cable installation process. These ducts are manufactured with pre-installed cables or empty conduits, which can be easily accessed and utilized for cable installation.

Cable Pulling Equipment

Cable pulling equipment such as cable pullers, winches, capstans, and cable rollers can be used to assist in the installation process. These tools provide mechanical advantage and help overcome friction and other installation challenges.

Preparations for Duct Installation Using an Air Blowing Method

General precautions should always be applied when handing optical fiber cable, such as not exceed the cable’s stated maximum pulling tension and stated bending radius, as well as not exceed the cable’s maximum crush load, and etc. In addition, other general safety precautions should be paid much attention as well. Before installation begins, construction planning also should be initialed. Last but not least, necessary equipment and materials are required for every installation, including inner-duct, cable pulling lubricants, a pulling eye or grip, a swivel, the cable blower equipment, and etc. For detailed information about preparation for duct installation, you should read installation manual carefully.

Duct Installation Procedure by Using Air Blowing Method

Step 1: Inspection for safety.

a.Prior to installation, all traffic safety zones, barricades, and flagmen must be in place.

b.Observe all local safety ordinances and practices. All manholes in the system must be checked for harmful gases and ventilation established.

c.Water should be pumped and any obstacles cleared.

d.Inspect manholes for general safety conditions such as ladders, existing cables, and rack conditions.

Step 2: Place blower unit(s), hydraulic and air supply equipment to establish connection between blower and receiving end, and all intermediate locations.

Step 3: Set up and align the reel.

a. Visually inspect each cable reel for physical damage.

b. Ensure the cable reel inner flanges are smooth and without nails to allow free payoff of the cable.

c. Set up the reel and reel trailer at the predetermined manhole location. Pay off the cable from the top of the reel.

d. Align the reel so that the cable makes a smooth transition through the blower and into the duct system.

Step 4: Attach the pulling grip to the cable or attach the swivel to the pulling grip's flexible eye to prevent the cable from twisting during the evolution. The swivel will later attach to the air carrier unit.

Step 5 to Step 11 are about setting up inner-duct and cable blower unit(s). Please refer to detailed equipment procedures on manual.

Step 12: Make adjustments at all the intermediate manholes for slack storage. At optical fiber cable ends and intermediate splice point locations, making sure to leave enough cable slack to easily reach an above-ground splicing vehicle plus 30 feet (9 meters) minimum.

Step 13: Slack coils may be assembled in a continuous direction loop configuration or a "figure eight". "Figure eight" configuration is best way to minimize torsion and stress in the cable fibers. "Figure eight" coil sizing should be approximately 15 feet (5 meters) end to end with each half loop about 5–8 feet (1.5–2.5 meters) in diameter.

Step 14: After the pulling is complete, cut 10 feet (3 meters) from the end of the fiber cable. Place a protective cap over the exposed cable end and tape it in place to prevent water intrusion. Coil any cable free ends and fix in place securely with cable ties to prevent damage.

Step 15: At all appropriate manhole locations, putting inner-duct in place. It begins from the center manhole and then the work towards the system ends. It is preferred that all exposed cable coils be mounted in a rack mounted closure box designed for holding the cable coil and the fiber splice closure.

Conclusion

Fiber optic cable installation into the duct provides both extra protection for optical fiber cable and an opportunity for future cable expansion. Optical fiber cable installation into the duct has widely been applied for telecommunication application so far.

Solution