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Comment by yuribit | Hacker News Reader

Some days ago we were discussing about sharks eating these calbes and how Google stops them http://www.forbes.com/sites/amitchowdhry/2014/08/15/how-goog...

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> James M. Barrett, a former deputy director of international engineering for AT&T , said that there were 55,000 or 60,000 miles of old undersea cable made out of copper that did not have a single case of shark biting, meaning sharks prefer to snack on fiber optic cables specifically. It is believed that the electrical current in the fiber-optic lines attract the sharks, triggering a feeding reflex.

"electrical current in the fiber-optic" but not copper?

I think that electrical cables have pretty low current. The fiber optic ones need to power amplifiers, so they have quite a bit of power going through.

I guess I figured copper wire would also required amplification.

Yes, copper cables have repeaters too. And I would expect them to work at similar voltages.

The only difference I can think of is that the amplifier power is probably a steady DC (and corresponding magnetic field) whereas the signal in copper will be varying voltages - creating a fluctuating magnetic field that repels the sharks ?

Fiber optic wire has a very high voltage wire to power the amplifiers. (Interestingly, it's only one. The ocean water provides the return path.)

I guess I figured copper wire would also required amplification.

Interesting on the return path. Where does the source connect i.e. one side of the "battery" goes to the amplifier (which returns to the sea, not the battery) and the other side of the battery goes to where? the sea?

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