I was always wondering about the following:
If lightning strikes directly into the phone line outdoors, can the excess power coming from the phone line jump over the switching power supply of the ADSL modem into the mains in the house and damage any computers / TVs / washing machines?
Let's assume that the ADSL modem is WiFi only and that there are no cables connected to it except for the phone line and mains.
There are many 'entry points' to your house for electrical disturbances, once lightning has struck close by, and the most important of these is the mains. A nearby strike will lift the ground potential, and induce a voltage into any wiring.
My anecdote is that I live in a row of houses. A house 4 doors up was struck by lightning. They needed to be totally rewired and replastered. Cables had blown out of their walls. Their neighbour's wiring survived, but they lost every item of electrical equipment, including simple motor-only things like fans. Their neighbour's motor-based equipment survived, but they lost all electronics. I lost only my ADSL modem, perhaps as it was connected to mains and the phone line, but all my other electronics survived.
Back in my hardware days, I was a technician repairing modems for a modem manufacturer. I repaired many modems hit by lightning strikes. They all had a couple large resistors connected to the phone line that would take the brunt of it. The smell of a fried 2W resistor is quite distinctive. I could tell it was a lightning strike when I took the case cover off. At most it would char part of the circuit board. I had to grind off the charred part, glue down traces from a scrap board if needed, the solder everything back up.
I never saw a power supply get harmed. I would think other things would be more susceptible to power surges through the mains than the modem. That's how we lose most of our electronics around here. So, don't worry about it.
It's unlikely. The wires of your telephone line are very thin and are close to ground at enough points to first vaporize before they can hit your washing mashine.
Let's assume that the ADSL modem is WiFi only and that there are no cables connected to it except for the phone line and mains.
If there is any vector for damage to your washing machine it's through mains, anyway.
Generally, lightning strikes into cables close to you are far rarer than people think they are (no, anecdotes don't change that). The likelihood of telephone lines being hit is smaller than that of power lines, because these typically hang higher for isolation purposes.
Multiply that with the small probability that damage to the phone system will propagate any further than the point at which the telephone line enters your house, and you'll find that you're worrying about something that is far less likely than your building collapsing onto your washing machine, computer and TV.
The probability of damage to electrical equipment through mains supply surges, after a nearby lightning strike, is much higher than that caused through telephone lines.
In my experience the failures have always been limited to power supply components.
In Austria I have seen such lightning damages years ago. At that time analog modems were in use and the computer the modem was connected to was sometimes destroyed. However, only devices that were directly connected to the modem were destroyed. WiFi did not exist at that time.
My phone line has been hit by lightning 6 times now in 2 years. Twice this month. The first time this month it took out our dish receiver, a 65” tv, our internet modem (all things plugged into a phone line). The second time (Saturday 7/10) our electronics were unplugged except our internet modem and it fried it yet again, as well as the phone line box inside and the wiring from the outside of the house to the inside. AT&T keeps saying it is well grounded outside. I call “BS”. Now if there is any lightning within 30 miles we unplug everything… if we are home.
