Introduction to Aerial Fiber Optic Cables

Introduction to Aerial Fiber Optic Cables

An aerial fiber optic cable is an insulated cable usually containing optical fibers required for a telecommunication line, which is suspended between utility poles. Network designers use Aerial fiber optic cable for aerial applications or cabling installation, utilizing the pole infrastructure common for power transport and is efficiently utilized by aerial fiber optic cable installations, reducing cost and installation time. In addition, aerial fiber optic cable resists environmental concerns such as ever-changing weather conditions in the form of excess heat and moisture and mechanical stress from line weight and external influences like vandalism and animal chew damage. Typical applications for aerial fiber optic cable are long-distance and network communication. This article introduces and discusses aerial fiber optic cable types, classifications, pre-and post-installation, and installation using a moving or stationary reel.

Aerial Fiber Optic Cable Types

Aerial fiber optic cables are divided into self-supporting or catenary cables that can be lashed to existing structures or lines. Self-supporting cable has cable bonded to insulated steel or all-dielectric messenger for support. A catenary cable is a regular outdoor loose-tube cable that is helically lashed to a pre-existing support line.

Installing Aerial Fiber Optic Cables

Aerial fiber optic cable is installed using a stationary reel or moving reel method. The stationary reel method is best used when there are obstacles along the planned cable route that reduce or eliminate equipment access. The moving reel method is used when the route is free from obstacles and obstructions, allowing easy or improved equipment access between the cable reel, the aerial section of placement, and a clear path alongside the poles for the reel trailer and trucks.

Pre-Construction Preparations

Careful planning and preparation are necessary before proceeding with aerial fiber optic cable installation. Conduct a survey of the proposed installation route and include all concerned parties. Consider details such as permitting, approvals, route clearance, and pre-existing poles and equipment.

• Conduct a pre-survey - inspect the route to determine the installation method, equipment, and material requirements most suited to the aerial fiber optic cable installation.
• Consider route issues - investigate ground conditions, clearance issues from roadways, trees, obstructions, and driveways
• Select splicing locations - Plan cable distances to select splicing locations that are at convenient non-hazardous locations. These locations should support the greatest length cable to reduce the number of splicing locations.
• Handling - Fiber optic cables can be damaged if not handled properly during the installation process. Adherence to the cable’s design limits of pull tension, minimum bend, and crush force during installation will ensure that the cable will perform properly throughout its full design lifetime. The greatest mistake when handling fiber optic cable is assuming that all outside plant (OSP) handling equipment is suitable for use.

Installation safety

Use properly trained personnel and make sure that conditions support the work. Work done during inclement weather can reduce safety. Use tools and equipment that are designed for the work being done and that function well. Be careful working near high voltage lines. When pulling cables, make sure that personnel and equipment do not get caught in the line. Failing to do these things may result in project delays and personnel injury.

Installation Guide to Aerial Fiber Optic Messenger Cables

Stationary Reel Method for Deploying Aerial Fiber Optic Cable

1. Attach the rope and stringing blocks and then pull the cable into place at each pole along the route. The radius of the stringing blocks must meet the minimum bending radius (under installation load or short-term load) of the cable.
2. During the pull of the cable onto the stringing blocks, Kellems pulling grips and a breakaway swivel that is rated at the proper pulling tension of the cable should be used to attach the pulling rope to the cable.
3. Position the cable reel directly in line with the installation route and use a tension limiting winch to pull the cable. Minimize tension during installation to keep the cable from breaking. Maintain communications at all times between all members of the installation crew so that the cable pull can be stopped when necessary.
4. When the cable is pulled it a final position, reduce excessive sag in the cable while allowing slack for splicing and secure both ends of the cable in place.
5. Once the cable has been secured with the dead-end hardware, the cable between the dead ends should be securely fastened to the poles by removing the cable from the stringing blocks and attaching the proper tangent support hardware.

Moving Reel Method for Deploying Aerial Fiber Optic Cable

1. Mount the cable reel on an aerial line truck or cable trailer.
2. Advance along the route while the cable is payed off of the reel. Avoid back tension, guiding the cable onto the pole and supporting it with the proper hardware. Check that there is sufficient slack available for splicing.
3. At each pole location, the reel must be kept at least 50 feet down the line from the pole while the cable is lifted into place on the pole.
4. J Hooks are used to temporarily hold the cable in place on each pole until a dead-end pole is reached.
5. Continue to install cable in each span of the route. Once a dead-end pole is reached, the messenger is tensioned for the correct sag level and terminated with dead-end hardware and attached to the pole.
6. Once the cable has been secured with the dead-end hardware, the cable between the dead ends should be securely fastened to the poles by removing the J Hooks and attaching the proper tangent support hardware.

Installation Guide to Lashing Aerial Fiber Optic Cables

Catenary fiber-optic cables that require support are lashed onto existing support wire for tensile strength and stability. Lashing using a stationary reel method, is typically used when the route is not fully accessible by support vehicles. Temporary blocks are placed on the messenger wire throughout the run. The fiber cable is pulled into place from a stationary reel located at one end of the section run. Once the cable is in position, the lashing operation joins the fiber cable to the messenger wire.

Lashing using a moving reel method, is used when the entire route is accessible by support vehicles. The route must be free of trees, limbs, and guy wires to allow full vehicle access. Support vehicles are used to pay off and raise the fiber cable to a position for the lashing operation to be performed along the length of the section run.

Lashing using the stationary reel method

1. The pulling grip to the cable and pull the cable slowly and steadily, ensuring that the cable is set properly on all rotating sheaves along the messenger route. Overserve cable tension throughout the pull so that the cable-rated tension is not exceeded. Tangent support blocks can be added at 30-50 foot intervals.
2. Once the cable is into position for lashing, pull sufficient slack for slack span and fiber cable splicing at the terminating pole. Apply a protective cap to the end of the cable and then fix both of the cable ends in place until lashing begins.
3. Setup and install lashing machine per instructions to the messenger and install the fiber cable to the lasher per vendor procedures. Commence the lashing operation per lasher operating instructions.

1. At each pole location, the lasher will be transferred to the next span. Use caution during transfers to prevent damage to equipment or injury to personnel. Pull enough wire out of the lasher to fully terminate the lashing on the span and/or for splicing and then cut the lashing wire. Transfer and reattach the lasher unit, cable positioner, and spacers to the messenger on the next span to be lashed. Reinstall the fiber cable into the lasher unit.
2. Repeat the above sequence for all remaining spans to be lashed. At the end of the run, verify slack span and cable splice length requirements prior to making any cable cuts. For any cable cuts or free cable ends, ensure the end is capped and taped to prevent water entry. Coil and secure any free cable end for later splicing.

Lashing using the stationary reel method

1. Position payoff vehicle in line with lashing unit, and raise the fiber cable to lashing unit guide chute and cable positioner. Pay off enough slack fiber cable to support fiber splicing at pole location.
2. Setup lasher unit per instruction manual and install lashing material into the lasher machine. Install the cable positioner and guide rollers onto the messenger wire. Secure the lasher to the messenger and install the fiber cable to the lasher per vendor procedures. Ensure any guides that close onto the fiber cable are snug but not too tight as to cause damage to the cable. Feed the fiber cable through the cable positioner and guide chute. Terminate the lashing using a lashing wire clamp and an appropriate cable spacer.
3. Commence the lashing operation per lasher operating instructions. Coordinate payoff vehicle movement with lashing unit progress. Payoff vehicle should be about 50 feet (15 meters) in front of the lasher.
4. At each pole location the lasher will be transferred to the next span. Use caution during transfers to prevent damage to equipment or injury to personnel. Pull enough wire out of the lasher to fully terminate the lashing wire to the messenger using a lashing wire clamp and an appropriate cable spacer.
5. Transfer and re-attach the lasher unit, cable positioner, and spacers to the messenger on the next span to be lashed. Fully terminate the lashing on the end of the previous span and on the end of the span to be lashed. Repeat the above sequence for all remaining spans to be lashed.
6. At the end of the run verify slack span and cable splice length requirements prior to making any cable cuts. As appropriate, make a cable cut or leave the remaining reel of fiber cable at the site. For any cable cuts or free cable ends, ensure the end is capped and taped to prevent water entry. Coil and secure any free cable end for later splicing

Post-Construction Inspection

Perform a post-construction inspection to ensure that the cable is straight and free of kinks or damage. Ensure that drip loops and grounds are installed properly. Also check that the cable does not touch trees, buildings, or other environmental obstacles.

Summary

Compared with buried cable or fiber in-duct solution, aerial fiber optic cable installation is typically faster and less expensive laying cable underground. It is also cost-effective because it reuses previously in-place structures and routes.