cable within 50 feet (approximate ly
15.24 meters) from its point of entry
into the building to meet NEC code
and NFPA requirements for a conventional
installation. Because the blown
fiber tube cables and not the fiber
bundles are outdoor, plenum, riser
rated and so on that meet NEC and
NFPA requirements, the tube cables
are connected with push-fit connectors
allowing for a splice-free continuous
fiber run at the point of entry
into the building.
When considering a blown fiber
solution for this application, the
conduit must be sized for the tube
cable. Assuming a 7-tube outdoor
tube cable will be installed, the out-
side diameter is 1.7 inches. There
have been concerns by some regarding
the size of tube cable, but the
advantages of the spare tubes for
future growth can certainly outweigh
this concern. In this instance, if 144-
count fiber is required from point A
to point B, two of the 7-tubes would
38 PATHWAYS VS. 3 PATHWAYS
2 - 19 Tube Cables
in 4" PVC Conduit
42 I ICT TODAY
be utilized, each with a 72-count
fiber bundle. This leaves five of the
seven tubes open. This would allow
for up to five more fiber bundles to
be installed for future use, thereby
leaving the flexibility for up to 360
strands of additional fiber to be
installed at a later date. In this example,
the footage from point A to
point B is approximately 3,000 feet
(approximately 915 meters). If the
customer should need to add a new
fiber run, it would take only two
installers around 30 minutes to blow
the new fiber into the existing tubes
compared to four or more installers
one to two days to install/pull the
fiber optic cable conventionally. Keep
in mind that the setup time for either
installation is not included in that
timeframe. With a blown fiber
system, the installer would need to
set up the blowing equipment and
nitrogen tanks. With a conventional
installation, the installer would need
to set up the reels and have proper
pulling equipment in place. The cost
difference for time and labor in this
scenario for blown fiber can be sub-
stantial to the customer, potentially
saving thousands of dollars.
Another scenario to consider
in an outside burial application is
an existing conduit situation. If there
is a 4-inch conduit already in place,
there would be room to install two
of the 19-tube cables, yielding a total
of 38 available tubes for immediate
and/or future use (Figure 8).
The 38 pathways through which
a maximum of 72-count fiber bun-
dles can be blown would give the
customer the ability to install up to
2,736 strands of fiber. Assume that
the customer only needs 144-strand
fiber at the time of installation and
is considering the conventional fiber
method. The customer would have
to decide whether to install the
144-strand needed now or whether
to install additional strands for the
future, just in case. A decision may
also be made to install some type of
mesh or plastic type innerduct to
make future adds easier; this too will
consume some of the space inside
the conduit. Customers often choose
to add additional fiber strands at the
time of the installation and pay the
additional cost up front; the fiber
remains dark for long periods of time,
thus costing the customer for something
they are not using. The advantage
in this case with a blown fiber
system is flexibility. The blown fiber
system offers fiber on demand, taking
the guess work out of accurately
forecasting future fiber requirements
and the opportunity and financial
3 - 1.25" Innerduct
in 4" PVC Conduit
FIGURE 8: Blown fiber versus conventional conduit example. costs associated with laying either