Buried Fiber Optic not immune to Lighting damage

mike95490

from the lighting protection group.
(note most industrial fiber optic has a steel armor sheath around the fiber, with layers of insulation and waterproofing in between )

Repetitive Holes punched through Fibre Optic Cable


A Telcomm Engineer from the east coast of Canada reported this
observation at a Surge Protection meeting.

An underground fibre cable was discovered to have holes punched
through the outer jacket's insulation about every meter for a length
of the cable.
The speculation was that surge energy was conducted onto the sheaf at
a ground point.
Then the surge energy propagated faster on the metal sheaf than it
did through the surround soil.
When the voltage rise on the metal sheaf exceeded the breakdown
voltage of the outer insulation, there was a punch through hole which
equalized the sheaf and the soil's potential.
The energy continued to propagate along the sheaf until the breakdown
voltage was again exceeded.
This occurred several additional times hence the fiber had to be
replaced.

Just another incident relating to propagation of energy through a
conductor vs the earth.

Regards
Peter Brackett, P. Eng
Signals and Communications,
Canadian Pacific Railway




http://tech.groups.yahoo.com/group/LightningProtection/message/2024

niel

Re: Buried Fiber Optic not immune to Lighting damage

now that's interesting as the electrical ground system allowed that lightning's energy onto the sheaf, but because it was insulated it couldn't dissipate to the surrounding ground without punching through it as it travelled along the sheaf. they need the grounded lead exposed to the soil at all times or in this case every meter or so to prevent this from happening again. another possibility may be to try and dissipate it where it entered the sheaf by having a large multirod grounding area that would appeal to the lightning better than the path of that sheaf by having a very low resistance to the surrounding soil area. easier to have exposed wire along the whole sheaf i think.