All glass fibre optics need a large radius for the bends. 1/4" radius will
definitely break any of the corning glass products we used to build a four
city wide MAN fibre optic network.
I was warned of this bend problem early in my installation training and
thought it was bunk. I was using electrical tape boxes (about 4.5" dia.) to
store spare flexible jumper leads for usage in the field instead of making
two trips from the site to warehouse each time. It took a few months to a
few years for the fractures to show up in the glass and become problems for
customers once they achieve high bandwidths and cannot attain them, due to
data errors...fractured glass strands = reflected light and bad light
conduction.
One day a contract cross country fibre optic company we used to do all our
splices, showed me, with his laser light indicator, what happens when you
bend the stuff too sharply. Red light spills out the sides at the fractures
and you can see it right throuygh the jackets too. Most strands never
recover but still work fine, depending on tolerable light losses. We stopped
storing the flex jumpers in small round boxes from then on. Behind the
scenes I began seeing all our installed jumpers being replaced due to data
errors (light impedance)....ooops!
Check the specs and although these jacketed outdoor cables with many strands
looks tough they cannot make the sharp bends. Most specs will tell you to
use no smaller than 2-3" conduit to enforce slow turns.
Shock?
A few incidents where cables between poles were hit, one by a dumptruck, and
a pole hit in an accident (IIRC), shattered some (or all) of the strands in
50 or 100 strand aerial cables. The contractors started cutting back cable
sheaths to find the start of the good glass sections and make a splice
there. One fracture from the dumptruck with dumper up, stretched the cable
so badly before snapping, the inside the fractured strands when over 1 km in
one direction and almost 1/2 km the other, due to longitudinal mechanical
shock. The injuries are restrung back to the nearest splice box now, without
test, and it it takes a few km of new cable it is faster and cheaper. The
drivers not looking pay big time for those ones.
Jacketed fiber is tough. One trick is to blow it into existing
underground gas pipes, with a little parachute/umbrella sort of thing.
A quarter inch bend radius has no effect on the stuff we use.
But shock?
John
