Comparison of Jelly Filled Copper Cable and Optical Fiber Cable Constructions-Part 1

Optical fiber cables have clear advantages over copper cables, an obvious reason why telecom operators prefer and switch to optical fiber cables to build their telecommunication networks. Let us see the comparison of construction of jelly filled telephone cable and optical fiber cable. This comparison is made based on my experience in both type of cables, but hope will provide a general idea of both types of cables.

Conductor: The medium for sending the signal in metallic telephone cables called the conductor. Conductor used in Jelly filled telephone cables for telecommunication network is a round wire of annealed high conductivity copper, smoothly drawn with uniform diameter and resistance. In an optical fiber cable, the equivalent conductor or medium is optical fiber, which is a thin, flexible purified silica glass rod coated with UV curable acrylate.

Insulation: In Jelly filled telephone cable each conductor is insulated with either solid medium/ high density polyethylene or Foam Skin polyethylene insulation. The conductor is insulated uniformly in various colors with extremely tight tolerances to help the cable meet the electrical and transmission requirements of specification. In optical fiber cable, equivalent is the secondary coating, which is either a tight buffered coating or loose buffered coating. Tight buffering can be done either fully tight or semi-tight. Alternatively, a 400 or 500 micrometer UV curable acrylate coating is provided over the primary coated optical fiber. Such extra coated fibers can be tight buffered to provide extra mechanical characteristics to the fiber.

Pairs: Individual insulated copper conductors are twisted together with a uniform lay to form a pair. The length of the lay of each pair is different from that of the adjacent pair to enable the cable to meet the capacitance unbalance and cross talk requirements of the specifications. The pairs have specific color combination for easy identification. There is no specific equivalent process in optical fiber cabling since fibers do not need to form pairs. A single fiber can be used to send and receive optical signals. The nearly equivalent process happens in secondary coating process, where the fibers are grouped in a loose tube. However, this grouping is not comparable to the copper pairs.

Units: For Jelly filled copper telephone cables, the twisted pairs are stranded in a single unit of 10, 20, 25 or more pairs and wrapped helically with an identification color binder. For cables having more pairs, a number of units are stranded together to form a super unit. A colored identification binder is wrapped around the super units for easy identification. Equivalent process in optical fiber cabling is the stranding (either SZ or helical) of loose tubes and or tight buffers. Different colored loose tubes are stranded around a central strength member, which then wrapped with binder yarns to hold them tightly.

Jelly Filling: In copper telephone cables, units or super units are laid up to form the core of the cable. During bunching, a water resistant filling compound is applied to fill the interstices of the laid up core. This filling compound acts as a dielectric between the pairs as well as a moisture barrier. The filling compound is compatible with polyethylene insulation whereby the cable’s electrical and physical characteristics are not affected. In optical fiber cabling, jelly filling during stranding is usually done in two stages. The first process is applying a thin coating over the central strength member, which is generally known as flooding process. The second process of jelly application is done after stranding of loose tubes, which is known as filling process.

This discussion will continue in second part………….Read the second part here: Comparison of Jelly Filled Copper Cable and Optical Fiber Cable Constructions-Part 2

Author: Praveen Gupta

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