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Lightning protection for your PSTN line?

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Joined: 16 May 2018
Posts: 11
State or Province: Alabama

PostPosted: Thu Oct 25, 2018 4:53 pm    Post subject: Lightning protection for your PSTN line? Reply with quote

OK, this became a sorta headache when I heard the story that my friend's DSL modem caught fire by some lightning surge that reached the modem over the PSTN copper cable. The ordinary strategy that I always use to protect my home network when there is lightning outside is, disconnecting the modem from the internet by removing the cable, so I can assure the fact that no lightning surge can reach my network through the copper cable. This might be the best solution unless you want to keep always connected to the internet. The thing I can't understand is how some big internet-dependent companies/factories keep the networks and computers at their workstations unaffected with any significance of lightning surge. For sure they use copper cables to connect with their ISPs, and they can't simply cut their internet off to be protected from surge. What sort of mechanism these people really use?

There are some "surge protectors" I can buy at cheap prices. Oh, and some APC UPS's come with a surge protectors for phone lines. Can these gadgets really protect you from lightning surge? What I'm not really sure about these gadgets is whether they can avoid a high voltage to be sparked and jumped to the output terminal and reach my network, even after the connection is electronically disconnected or whatever thingy happens inside. I know there might not be a perfect solution, but what would be the best solution that you can you use to protect your expensive machines from lightning surge that comes over 'internet'?
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Joined: 19 May 2018
Posts: 16
State or Province: Maine

PostPosted: Mon Oct 29, 2018 6:58 pm    Post subject: Reply with quote

A direct lightning strike means hundreds of thousands of joules must dissipate somewhere. Protection means you know where energy dissipates. A protector (hundreds of joules) will somehow block or absorb a surge? Only when profits create myths.
Some protection systems do not even have protectors. But every protection system always has what does all protection - single point earth ground. Hundreds of thousands of joules dissipate harmlessly outside the building when a direct lightning strike is connected to and is absorb by earth. Either that current goes to earth before entering a building. Or that current goes hunting for earth via appliances, destructively. Your choice.
Some incoming wires (cable TV, satellite dish) connect directly (low impedance) to earth. Other wires cannot be earthed directly. So a protector makes the same low impedance (ie less than 10 foot) connection to earth. That distance and other parameters are critical. And that explains why every telco CO suffers 100 surges per storm without damage.
The most common source of surges are utility wires most exposed - AC electric. A direct lightning strike to AC wires far down the street is a direct strike to every appliance. The incoming path is obvious. But to have damage, an outgoing path must exist.
All telco and cable wires are required to have effective protection. AC electric is not. How does that surge, incoming on AC mains, also go outgoing to earth? A common path is via a telephone or cable modem. Incoming on AC mains. Outgoing via signal wires. Damage is most often on a modem's outgoing path.
The naive (using observation) see damage on the outgoing path. Then assume a surge was incoming on the cable or phone wires. Also forget that both an incoming current path and an outgoing current path must exist
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