I am a software engineer with only a basic experience with electric/electronic engineering. I live in a rural area subject to thunderstorms, my house is the end of the line from street poles. It's common to receive lightning strikes by energy line. I have grounding, surge protectors, etc, but somehow sometimes a surge is capable to hit and damage my UPS.

It's a common recommendation to unplug sensible/expensible eletronics on thunderstorms. I am wondering if it's possible to automate this process.

With an Arduino it's not so difficult to make a "lightning detector". This could cut-off mains power from some equipment on a thunderstorm and turn it back on when it stops.

I am not sure circuit breakers, relays or contactors are able to isolate a lightning strike because of the small air gap between contacts when they are off. In other hand, if you consider that a lightning is capable enough to jump from a cloud in sky to the ground, even if you unplug an equipment from the wall, a strike could jump from the wall to the disconnected plug. If you imagine, for a very small probabillty, that NO ONE is safe.

So, I ask, there is some kind of relay appropriate to isolate a lightning strike?

  • \$\begingroup\$ If you consider the huge distances the lightning can jump, no gap smaller than that (thus smaller than your house) could help. But really, where do you live that power lines get regular hits by lightning and no protective equipment is installed here? \$\endgroup\$ – PlasmaHH Apr 11 '18 at 14:29
  • \$\begingroup\$ Brazil, the country that has lightning strikes than almost anywhere in the world (by coincidence, also the country with the largest tropical area). \$\endgroup\$ – TNT Apr 11 '18 at 14:40
  • \$\begingroup\$ What kind of protective equipament are you suggesting / talking about? I've two separated sets inside my area (two different places and groundings) of 60kA surge protectors in each phase. If I use surge protectors smaller than 60kA they don't last a month. \$\endgroup\$ – TNT Apr 11 '18 at 14:43
  • \$\begingroup\$ the power company should have installed things that lower the possibility of the power lines being struck \$\endgroup\$ – PlasmaHH Apr 11 '18 at 14:45
  • \$\begingroup\$ "... a strike could jump from the wall to the disconnected plug." Extremely unlikely as you will also have disconnected the earth so there is no "advantage" in jumping to the equipment - particularly when the earth in the wall socket is so much nearer. \$\endgroup\$ – Transistor Apr 11 '18 at 14:47

You don't unplug electrical equipment to protect it from a direct lightning strike. You unplug it to raise its damage threshhold, to increase the likelyhood of its surviving a nearby strike. As such, opening any contactor or relay would be beneficial.

I live in one of a row of houses. A few years ago, another house in the row was struck by lightning. Let's call this house zero. They lost all their electrical equipment, and had to be rewired. House one next door lost all their electrical equipment. House two lost only electronic equipment, simple electricals with motors and dumb switches still worked. In house three, I lost my ADSL. House four survived with no damage.

So there's plenty of scope for a small break in the wiring to reduce the scope of your loss with a close, but not direct, strike.

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The key to providing isolation from lightning is to not only open the circuit to your normal loads, but also provide a shunt path to ground that has a smaller gap than the isolation switch. That way, when lightning strikes, the current flows through the shunt rather than trying to jump the gap in your isolation device.

This is why, for example, your landline phone service entrance has gas-discharge tubes across the wires and between each wire and ground. Similar devices are available for mains connections.

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  • \$\begingroup\$ I wish they had, here all I've get is a bunch of twisted pair wires, the rest is my responsibility... \$\endgroup\$ – PlasmaHH Apr 12 '18 at 7:32

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