The guy who put it up for me said I must turn it off if there is thunder or lightning. Is that true? If u also have fibre do u do that?
No reason that fiber will mean better protection for many reasons.
For example, fiber also has a messenger wire that serves many functions. For example, to make possible locating a buried cable. It is also a potential incoming path for a surge (ie lightning).
In one venue, their printer, computer, and ONT (fiber optic interface) were destroyed by lightning. Reason is obvious once one learns why damage occurs. A destructive surge is a current incoming and outgoing through some appliance. An outgoing path to earth is obvious - that ONT. Incoming path may be numerous. In this case, I replaced various semiconductors to restore all electronics (except for an ONT that was replaced by its ISP).
Meanwhile, nobody need power off or disconnect during any thunderstorm. Or does your town terminate phone service during every storm to protect their their multi-million Rand computers? Of course not. Telco switching centers (and that computer) suffer about 100 surges with each storm. And no damage. Because they do what you must do both for fiber and copper connections. Because they do what was done more than 100 years ago to even have direct lightning strikes without damage.
If your ONT (and other appliances) are at risk during a thunder storm, then turning it off does nothing. In one case, they foolishly used plug-in protectors on a network of powered off computers. Those plug-in protectors earthed a surge directly through that network - damaged many computers. We traced that electrical current path by literally replacing each damaged IC. We knew exactly how that surge got into and went out of each damaged electronic box.
Did you really think a millimeters gap in a power switch might stop what three kilometers of sky could not?
He who made a power off recommendation clearly did not know why a risk exists, how surges do damage, and how to avert damage. Fiber does not guarantee protection. Power off also is not protection. Protection even for fiber optic facilities is what was a proven solution even 100 years ago - proper earthing so that a surge does not enter a building. Required for many reasons including and not limited to a messenger wire that exists with an incoming fiber.
