Conduit in a concrete slab
Outside plant cabling: Making
sure you get it right
Ensure your campus connectivity is
up to the rigors of the outdoors.
BY RON TELLAS, Belden
How can you expand the reach of your
cabling systems and enterprise networks? By using outside plant (OSP) cable to run infrastructure underground
or overhead, you can extend your networks to the outdoors, reaching across a
With outdoor ratings, OSP cable stands out from traditional indoor-rated copper or fiber cable for its
ability to maintain performance despite
harsh conditions. It’s designed to withstand flooding, moisture and high and
low temperatures, and resists abrasion
Where OSP cable should be used
Usually, OSP cabling extends between
separate structures. The National Fire
Protection Association (NFPA) requires
that unlisted OSP cabling be terminated
within 15 meters (50 feet) from its point
of entry into the building, either through
a wall or through the flooring. At this
termination, the structured cabling
transitions to listed cabling and continues to connect the enterprise network.
A listed cable is one that is certified by
Under writers Laboratories (UL) for spe-
cific flammability ratings and listed for
its intended use: usu-
ally CM, CMR or CMX.
A listed OSP cable can extend beyond
the 15-m/50-ft limitation, and can also be
used within enterprise
buildings in other applications where the
OSP cabling are of
One common application that calls
for OSP cable involves conduit in concrete slab. In many of today’s new assisted-living facilities being built around
the country, for example, you may notice
the conduit (either plastic PVC or metal
EMT) that sticks up out of the concrete
slab during construction or renovation
projects. The conduit often used in these
applications is designed to run wires
and cabling from a centralized location
to many specific locations or endpoints.
But oftentimes inside this conduit,
you’ll find indoor-rated cable—a typical
Category 6 cable, for example.
This situation represents two common mistakes made in applications
where listed OSP cabling is better suited.
1. The project team assumes that normal, indoor-rated cabling will perform well in outdoor applications as
long as it’s protected.
2. The project team assumes that conduit is enough of a protector for indoor-rated cable.
As any contractor or building owner
will tell you, structures move and crack
as they age and settle. Eventually, as the
ground and concrete shift, conduit can
be damaged. If the conduit cracks, water
can infiltrate the conduit. If the cables
inside that conduit are indoor-rated,
we’ve got bad news: They’re not designed to handle any moisture, so the
cables won’t be able to maintain performance. The result? Network downtime,
Placing plastic or metal conduit inside a concrete slab is a
common approach on campuses such as assisted-living
communities. Project teams should not assume that
indoor-rated cabling can be placed inside such a conduit.