Telecom Ducts: Long-haul Vision

A telecom duct is a long-term investment. Network builders, pipelines, other
right-of-way owners who typically buy telecom ducts are making a decision for
the long haul. They are people who expect to be around for a long long time.
Like the city planners of a century ago, they have to be visionaries. They have
to think far into the future as they lay their networks. The networks willl be
used to provide service to consumers and their complete satisfaction is of
paramount importance. The networks necessarily have to be future proof.

The city planners who envisioned and built the London Underground or the
Paris Metro a hundred years ago knew they were building a transport system for
Londoners and Parisians generations into the future. They built these systems
when these cities were still growing and the urban centers had not yet seen
today’s mushrooming growth of population. They were thus able to build
stations and networks of lines in the bowels of earth which as people-movers
more than rival the urban sprawl of flyovers and highways which have sprung up
with the invention and subsequent proliferation of the motor car. Despite the
advent of the motor car even today the city dweller or any visitor to these two
metros would find it more convenient and faster to travel by the UG or the
Metro. The reason they continue to be the preferred mode is because of the
durability and flexibility that the visionaries built into these systems. As
technology advanced and more and more comfortable and speedier rail cars became
available they replaced the earlier outdated versions. Yet the infrastructure
built then continues to this day and into the future.

The fiber optic telecom network builder today need not despair. He has
sufficient flexibility at hand to build a future-proof fiber optic network. He
merely has to be cognizant of all the opportunities available to him and he need
make no compromises on quality, durability and flexibility. There are ducts
customized to meet his every need. But like the city planner of yesteryear he
needs to be a visionary. Buying of the duct is investing in infrastructure. The
cable that goes into the duct is like the rail cars in the Underground or Metro.
As fiber optic technology advances the cable like the rail cars can be replaced.
However, the duct should retain its integrity. Further, the duct should be such
that it eases the installation of the cable, and when obsolete, its removal, and
subsequent replacement.

Choices for Long-haul
The telecom buyer has a choice of two ducts for the long haul: both long
life as well as long distance. Ducts conforming to American Standards for
Testing Materials (ASTM) and those that pass the Environmental Stress Crack
Resistance (ESCR) test for 1,000 hours can be considered good. This test
establishes a duct life of 50 years.

Ducts are there

interests with the obsolete technology continue to promote the use of
200-meter ducts with pre-inserted ropes

Pulling of
cables by ropes damages ducts

Plus, cable
lengths are limited to 2 km

solid lubricated duct with jetting technology makes 4-km cables the 

Such ducts are ideal for cable installation through jetting technology. The
permanently solid lubricated silicore lining minimizes friction between the
outer wall of the cable and the inner wall of the duct. The cable is blown and
flows easily through the length of the duct. The cable is not stressed as it is
when installed through pulling. The minimal friction facilitates blowing of upto
2 km cable at a time. At the time of replacement the existing cable can be
deblown just as easily. The other advantage of stress-free installation by
blowing is that it enables the use of unarmored cable. Installation of cable by
pulling on the other hand results in stress that may necessitate the use of
armored cable. Unarmored cable is lower cost than armored cable.

Other ducts for the long-haul are available, which are designed for enhanced
blowing performance. A network builder looking for a rapid roll-out of the
network could be well-advised to go for this duct. The duct has a spirally
ribbed inside construction reducing the area of contact between the cable and
the duct and thus the friction. Additionally, the swirl of air through the
spiral ribs provides a stronger cushion to the cable. The result is a speedier
installation of cable over the same length and the possibility of blowing longer
than 2 km cable in a single shot. Use of this duct will enable the use of 6-km
cable drums in place of the 4-km cable drums currently in vogue. This offers the
additional advantage of reducing the number of splicing points, improving the
quality of the signal, and reducing overall cost. These are recurring advantages
as and when the cable is replaced over the long life of the duct. Deblowing of
the cable to be removed is as speedy and easy as the blowing.

Yet another type of duct is designed for easy traceability of the duct
underground and also for checking the depth of the installed duct. This is the
usual smooth walled duct with a copper wire co-extruded along the length of the
duct to facilitate identification and location of the duct. This duct finds
application within the city as well as on inter-city routes. In urban areas its
use helps in pinpointing the exact duct location so time is not lost in digging
up sidewalks and built-up areas on a hit-and-trial basis. The right-of-way is
congested with various lines and underground installations and this duct
prevents misplaced diggings and resultant penalty. It facilitates quicker
maintenance and upgradation of the network.

Use of such ducts on long-haul routes along highways is strongly recommended
again for ease of identification and quick location of the ducts, as drawings
cannot always be relied upon since over a period of time highway expansion and
route changes take place.

Ducts for Cities
The city environment poses a challenge. Digging in the city tends to be
expensive. Permissions for digging are difficult to obtain. During the monsoon
months many municipalities refuse to give digging permission because of the
water logging problem from the rains. The network builder has to keep the
network running at all times. In the case of a fault he needs immediate access
to rectify the problem and have the system up again. In major metros, there are
areas where due to underground congestion further underground installations are
simply banned. What does the network builder do in such a situation? Fortunately
there is a solution. Look at what the Delhi Metro builders are doing. Go above
ground. The solution lies in the use of ducts for aerial networks. These ducts
are clamped to utility poles 150 to 200 meters apart. They have in-built
rigidity which prevents any catenary formation between poles. The marginally
higher initial investment is easily justified by ease of maintenance of the
network in the difficult and congested city environment.


It is not enough to know what duct to buy. The more important question is where to buy, or who to buy from. Buying ducts is not as simple as buying pencils. Unfortunately, some buying organizations have difficulty in making the distinction. These are the people who make the decision on the basis of the bid price alone. The buying of industrial products is a more sophisticated process and the bid price alone should never clinch the decision in favor of any particular supplier. 
A buyer of ducts should consider these aspects when selecting a supplier:

The reputation of the supplier

The manufacturing capability of the supplier

The quality control in place in the supplier organization

Ducts should be the reason for the supplier’s existence (it should be his core business, not an adjunct business)

Technology and technical competence of supplier

The supplier should offer the complete range of products

The training capabilities of the supplier

The supplier’s ability to offer the total solution including testing of the laid duct for its suitability for cable blowing, duct rectification, and finally cable installation through blowing

All the ducts we talked about so far are great for long-distance networks or
networks circling major cities. What about local access networks? Let us go back
to the analogy with the Underground or Metro systems. The builders of those
systems built interconnecting links at specific stations from one line to
another. Similarly, for local access networks, the current practice has been to
provide for cable loops at various potentially high-traffic points around the
city. This practice leads to a bigger investment for some future demand.
Additionally, the cable has to be spliced to meet that demand. Fortunately,
there is a better way to meet the needs of the local area network. The answer
lies in micro ducts. These are very small ducts that, like cable, can be blown
into the main duct. A micro cable consisting of a few fibers can be blown into
the micro duct as and when there is a demand at a local area network. There is
no longer a need for splicing from the cable loop to provide connection in the
local area. No splicing means no interruption of service. No unnecessary cable
loops means no more dead or dormant investment in cable and loop pits.
Investment in micro cable can be deferred until such time that the demand is
there and further network is built with latest available fiber technology.

The ribbed in/out ducts are designed for use as sub-ducts in existing main
duct underground systems. These ducts are the answer to fast and efficient duct
and cable placement in existing systems. The outer rib on the sub-duct reduces
the surface contact area and therefore the friction between the sub-duct and the
internal surface of the main duct through which it is pulled during
installation. The interlocking outer ribs of sub-ducts as they are pulled
through the main duct reduce spiraling during installation ensuring a straight
installation. The combined beneficial effect is the need for a reduced pulling
force to pull the sub-ducts through the main duct. A straight sub-duct results
in stress free cable installation through blowing ensuring better network
quality. The inner rib reduces the area of contact and resulting friction
between cable and duct further easing the cable installation.

Special-purpose Ducts
Special fire retardant ducts are appropriate for use in those applications
where fire hazard and human safety are concerns. These ducts have found use in
tunnels and in regeneration stations in the laying of networks. Other
applications are in hospitals, hotels, mines, movie halls, high-rise buildings,
and mission-critical, strategic importance buildings. Use of these ducts is
recommended wherever there is a fire hazard.

The double-wall corrugated duct is another special duct. It is suitable for
road and rail crossings. It is the ideal solution for replacement of galvanized
iron (GI) pipes, PVC ducts, and reinforced concrete construction (RCC) pipes in
network build-ups.

Finally, we come to the large diameter ducts of up to 110 mm in diameter.
These ducts areappropriate for installation of copper cable for the last
kilometer telecom application.

Buying Considerations
The track record of the potential supplier is important. How long has he
been in the business, how many kilometers duct has he supplied, how many
kilometers cable has he blown? There are four or five known instances where the
duct supplier for whatever reason has failed to complete the blowing of the
cable in the duct supplied by him. In such situations the network builder has
had to prevail on some other reputable supplier to come with his blowing
resources to complete the job.

The network builder in buying ducts should look for a supplier who has a
long-term commitment to the market. Tomorrow or whenever in the future he needs
support he should be able to call on the supplier. The person who has made a low
bid to gain the business will have to cut corners to make a profit on the deal.
The sample submitted for gaining approval as a qualified supplier may be quite
different from the quality of the supply finally delivered to the field
locations, as has been established by the results of tests carried out on field
samples. The thickness of the duct may not be uniform throughout. Sometimes
claims are made about ducts being homogeneously solid lubricated, but the high
cost of such a duct belie the claim as no more than mere words. These problems
can be averted through specification of third party inspection of field
deliveries in purchase contracts with outright rejection of the entire quantity
supplied against deficiencies.

Is he a supplier of duct alone? Or is duct selling an incremental business
for him. The core business may be something else. Tomorrow he may give up on the
incremental business and revert back to the core business alone. On the other
hand, the supplier who has invested in manufacture of ducts alone will
concentrate on making innovations in his field and in addressing his customers
problems and needs through long-term relationships with them.

Look out for these Features

Independent tests conducted on field
samples drawn from factory-approved supplies to some network builders found most samples failing on one or more of these tests on account of use of recycled substandard polymer:

Ovality (leads to leakage at couplers)

Elongation (less elasticity; more rigid)

Oxidation Induction Time (OIT) Test (duct life-related; indicates inadequate use of expensive antioxidant)

Impact Test (for brittleness)

Undersized Thickness (thickness of duct less than specified)

High Filler Content (use of filler instead of HDPE polymer)

Internal Coefficient of Friction (higher than specified: 0.08 instead of 0.06; increased friction makes cable blowing more difficult)

Thickness of Lubricant Layer (7 percent or 8 percent against specified 10 percent)

Vested interests with the obsolete technology continue to promote the use of
200-meter ducts with pre-inserted ropes. The problem with pulling of cables by
rope is that the pulled cable and the pulling rope both damage the duct. In
addition the pulling action stresses the cable with potential for damage of
fibers. The short duct lengths result in the use of many more couplers with
added possibility of coupler leakage. Pulling by rope requires the use of
external liquid lubricant. This gradually solidifies and at the time of system
upgradation cable removal and replacement becomes a major problem. The use of
1-km ducts with rope pulling aggravates the damage to both ducts and cables.
With this obsolete technology cable lengths are limited to 2 km. Use of
permanently solid lubricated duct with jetting technology has made the 4-km
cable drum the norm in India. In the West 9-km cable drums are already in common

Can the supplier offer training to the duct buyer and his people on the
proper techniques for installation of the duct, the testing of the duct
integrity in holding pressure to establish readiness for cable blowing, and the
blowing of the cable through jetting technology? This establishes the extent to
which the supplier is committed to helping the buyer. The requirements of the
purchase contract may be fulfilled by delivery of the duct, but the committed
supplier will be concerned to ensure that the buyer receives full value for his
money through a long-life easily installable quality network.

The buyer is not interested in merely buying duct. He is looking for the
total solution. He wants a speedy roll-out of his network so that it is up and
running. His core business is running the network with maximum up-time. Whoever
can help him achieve this by providing quality ducts, installing and testing the
ducts, and blowing cable through them is the ideal supplier. The buyer would be
happiest placing the order on the party providing the total solution.

The key to buying duct therefore lies in selecting the appropriate duct for
your application and more importantly in selecting the duct supplier. Select the
best supplier who can meet all your needs, address all your requirements, and
work with him. Of course, once you have selected the supplier, negotiate the
best possible package with him.

Ashok Kapur
director,  Duraline—Plumettaz Academy

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