FIBEROPTICS BY JIM HAYES
Splice closures come in two basic
styles. In inline-style closures, cables
enter from either one or both ends, and
the closure splits down the middle in line
with the cables for access. In a dome closure, cables enter from one end on a base,
and a single-piece dome drops down
over the splice trays.
Splicers like to argue over which
design is better, and arguments for both
can be persuasive. It’s probably a matter
of which type you learned on or have the
most experience with. Either can work
well if handled with care.
Sealing is a very important issue
with splice closures. Outdoor closures
must be well sealed to protect the fibers
and splices from the outside environment. Allowing moisture, dirt or mud to
enter the closure will surely cause long-term fiber performance and reliability
Winter is especially hard on closures.
A few winters ago, an installer sent me a
photo of a closure that leaked and then
froze solid. He called it a “splice-sicle.”
Splice closures generally have big
O-ring seals and clamps or screws that
hold the parts together to ensure seal
integrity. Complaints about poor sealing
on cheap closures and counterfeits are
common, so buying a brand name from a
reputable dealer is highly recommended.
Double-check the joints on the closure to ensure they are properly sealed.
Be especially careful around the cable
entrances. If the closure does not seal
and moisture gets in, it will cause problems with the splices, fibers and cables.
Some closures can be pressurized to test
the seal, so be sure to do so.
Cables must also be firmly attached
to the closure mechanically to ensure
they do not pull out. Closures will have
clamps near the cable entrance to clamp
and tie off cable-strength members.
Cables with metallic elements must also
be grounded properly.
After the splices are made and the
closure is sealed, it and the excess cable
must be mounted in a safe location. The
closure placement and excess cable
should be carefully considered to ensure
its safety and accessibility in case it needs
to be entered in the future for repairs or
Splicing is generally done in a splice
trailer where temperature can be kept
at a reasonable level and dirt and dust
exposure can be minimized. The trailer
also has a workspace with room for the
opened closure, splice trays, the splicing
machine, tools and supplies. When splicing cables, it takes an extra 10–20 meters
of cable to reach into the trailer, so that
excess cable will need to be stored in service loops near the closure.
If the cable is underground or direct-
buried, a pedestal, vault, hand-hole or
manhole will usually be installed to store
the splice closure and protect it. Direct-
buried cables should also have a pedestal
or hand-hole for the closure, not simply
buried near the cable where it is subject
to leaking and hard to find when problems
arise. Because pedestals are vulnerable to
damage from vehicles, they should be
placed as far as possible from roads.
Aerial cables are usually spliced on
the ground, so there may be a lot of extra
cable for storage. Sometimes the closure
is placed on the ground, and the cable is
coiled up on the pole or tower. The clo-
sure may be placed on the pole or tower
with coils of cable nearby. Closures may
even be suspended from the cable mes-
senger itself and the excess fiber lashed
to the messenger. Installers in some rural
areas have told me these visible closures
are popular for target practice. I have
also heard of them being attacked by
Our splices are almost completed,
but as you are always reminded, the job
is not completed until the paperwork
is done. The documentation on a splice
point must be comprehensive, including cables splice and every fiber splice
identified as cable to cable, loose tube
to loose tube and fiber to fiber. Ribbons
must be noted as ribbon to ribbon. Any
crossing or breaking out of fibers must
also be noted. And, of course, the spread-sheet used to document this will also
have test results.
That can be a lot of documentation if
you are splicing two 144-fiber cables, but
if a problem arises, having that documentation will make identifying fiber and
splices much easier, facilitating repair
More Secrets to Share
Achieving (splice) closure
FOR SEVERAL RECENT COLUMNS, I have been writing about splicing optical
fibers. Last month, I covered managing fibers inside the splice trays and closures.
But there is even more to know about splice closures.
HAYES is a VDV writer and educator and the president of the Fiber Optic Association. Find
him at www. JimHayes.com.