I have a case where phone landline is above the ground and when lightning strikes it hard, the internet modem and router gets damaged, including devices connected to it.

I was wondering what would be essential components of some sort of surge protector. I would expect it to look similar to surge protectors in electric installation which trips when the voltage spikes but I'm not sure it would be sufficient to protect such delicate (low voltage) equipment.

the devices i can quickly find online usually just give you a third terminal to connect to ground but I doubt it's all you need to have?

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    \$\begingroup\$ Most good surge protector power strips will also have surge protection terminals for a phone line and/or cable internet/tv. \$\endgroup\$
    – Hearth
    Commented Jul 28, 2021 at 15:29
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    \$\begingroup\$ Does this answer your question? What kind of protection do these Ethernet "surge protection" diodes provide? \$\endgroup\$ Commented Jul 28, 2021 at 15:31
  • \$\begingroup\$ The most essential is.. a phone line surge protector. So you can already buy a ready made product. \$\endgroup\$
    – Justme
    Commented Jul 28, 2021 at 15:46

1 Answer 1


A good protection network will use multiple types of protective devices which compliment each other. To be able to withstand lightning strikes, a common first device is a gaseous discharge tube - a spark gap. During an overvoltage event these can conduct thousands of amps but the voltage at which they activate is relatively high and cannot be made precise: +/- 20% is what you might expect to see.

After the GDT, you might have a metal oxide varistor. These also conduct when the voltage across them rises to a preset level, but they're more precise (+/- 10%). They cannot conduct as much current as a GDT, but they're just working with whatever is left over after your GDT did its job.

Finally, you might have a transient voltage suppressor - a kind of Zener diode. Same story as before: even more precise than a MOV, but at the expense of current handling capability.

On top of all of this, you have to take into account how all these devices are interacting with the line you're trying to protect: leakage current, additional capacitance, etc. If you're trying to protect a high speed data line, my suggestion is not to roll your own, but to buy a premade network that is designed for the line where engineers have already thought about these things.

  • \$\begingroup\$ Thanks. I didn't attempt to make my own, but to try to understand what's important to look at to differentiate not-to-useful products from ali compared to high quality products from elsewhere. The data speed is below 80Mb thus not that big but I can see that these number of options to pick from on consumer level is scarce. \$\endgroup\$
    – Mike
    Commented Jul 28, 2021 at 16:48
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    \$\begingroup\$ I would try a place like L-com for a data line surge protector. Most of the consumer grade stuff is well enough but at heart it's really only designed to protect a TV or desktop computer. \$\endgroup\$
    – vir
    Commented Jul 28, 2021 at 17:20

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