What happens when fiber breaks? [telecom]

Per Bill Horne:

Or some wacko figures out where the trans-Atlantic cables come to shore and blows it up....

We can be pretty sure that won't be in Fargo. But it won't be hard to figure out where, the info is available from various sources, including permits and navigation charts. Cryptome (sort of a predecessor of wikileaks) even publishes maps and aerial photos...

Well, then, thank Ghod for all those satellites, safely out-of-reach up in the Clarke belt.

Bill Horne Moderator

An almost-fail-safe solution to the cut-fiber problem is route diversity. Either two separate fibers from A to B over different routes (and if possible, carried by different carriers), or a loop from A to B to C to D to ... and back to A. With a loop every point should receive the identical signal from both directions (possibly offset by a few milliseconds) A failure in any leg of the loop doesn't cut service to any point, and makes it possible to identify the failed leg.

Another consideration is route location. Underground routes are subject to accidental cuts (as the case at hand illustrates) when located along or near public roads, and especially in urban and suburban areas where they may be damaged by construction activity nearby, or in the roadway itself. Pole-mounted routes are subject to thermal expansion/contraction, wind, icing, squirrels, guns, drunk drivers, oversize trucks, and fires.

Probably the safest underground routes are along railroads. Most mainline railroad rights-of-way have been stable for a century and likely to remain so even if they get converted into hiking/biking trails. Conduits on the sides of, or under, bridges often carry communications fibers.

The safest aerial routes use OPGW (optical ground wire) in which the fiber is encased inside the steel "static wire" at the top of transmission lines. See, for example:

The static wire is grounded and is intended to protect the power conductors from lighting.

One of the first companies to build an OPGW line was Norlight, based in Madison, Wisconsin. Norlight built an OPGW line from Minneapolis to Maple Grove, Illinois, along existing electric power transmission lines. At Maple Grove they connected to underground fiber leased from Williams Communications, Inc. to extend the link to downtown Chicago. In the years since Norlight has expanded its network throughout Indiana and Michigan.

Disclosure: I served as a contractor at Norlight during the early construction phase of the Minneapolis-Maple Grove segment.

Neal McLain

I thought the extra wires on three-phase transmission lines were used to carry the imbalance currents, and that the long-haul high-tension wires were connected in "Wye" fashion and would need the extra wire as a ground. Not so?

Bill Horne Moderator

I believe the higher voltage transmission lines are normally connected "delta" meaning there is no imbalance current. The distribution lines such as the ones that run down your street usually are connected "wye" and have a neutral for any imbalance current.

It's not hard to figure out. The large signs saying "DO NOT ANCHOR HERE" and "CALL 800-555-1234 BEFORE EVEN THINKING OF DIGGING" tend to be a giveaway.

R's, John

I believe they are Delta.

My question is: when (not if) that OPGW takes a lightning hit, and carries oh 100,000 Amps to ground....how do they ensure the glass is not damaged by the heat?