Should I turn off my computer during a thunderstorm?

I've heard that you should always turn off and unplug a computer during a thunderstorm. What would happen if I left my PC on and lightning struck my home?

• Answer:

  It might take you a while to get around to wondering about your PC if your home took a direct lightning strike. Let's imagine a lightning strike merely near (not even directly on) a power or phone line down the street somewhere. This is what actually happens regularly, and we will take it as a given that the closer to the wire and/or your house, the worse it gets. And understand that this actually applies to any electrical/electronic equipment in your house to one extent or another, your PC being among the most vulnerable. Lightning striking close to a wire (power, electric, cable, whatever) can induce hundreds, thousands, even tens of thousands of volts momentarily. It is frequently enough to break down the insulating property of semiconductors, which sometimes takes only a couple hundred volts. Depending on the device, it might be able to withstand a brief over current or reverse current, it might suffer slight damage (so that it still seems to work, but acts funny and nobody knows why), or it may be simply destroyed instantaneously. If it enters through the power line, maybe it will only blow out the power supply and stop there, or maybe it will continue on through and damage the motherboard, expansion boards, or drives. If it enters through the Internet connection, maybe it will only blow out your modem, or maybe it will pass on through, etc. Parenthetically, this is also why you're advised not to talk on the telephone during a storm. A nearby lightning strike can induce a voltage which can cause a pop loud enough to damage your hearing. Phones are even caused to explode now and then. Many devices do not have a hard or mechanical power switch. They have soft power switching, so that the power supply is never disconnected as long as it is plugged in. Turning them off is sort of an illusion, it just puts it into a very low power state. That's why unplugging them is the only solution. There are two impracticalities to unplugging. One is, they can't all be unplugged readily (see below). The other is, a thunderstorm which comes up while you're home isn't your only worry. Maybe you just didn't anticipate a storm when you left home, maybe a car hits a pole or a tree limb falls across a wire, maybe the power company is simply doing some maintenance somewhere and flips a switch. Any of these can create damaging voltage spikes. Phones, answering machines, fax machines, modems, cable TV and the like have a dual vulnerabilty because they're connected to other outside wiring besides just power. So I have two words for you: Surge Protector. Along with three other words: A Good One. Which work properly only if your house has a good, genuine, earth ground; not a "bootleg" ground strapped to the neutral. Used to be, you could get a surge protector for the one or two particularly susceptible devices. Now, your house may contain dozens, with microprocessors controlling everything from your A/C to your toaster. Cell phone or PDA plugged into a charger? Yep, at risk. That's why many people now use whole-house surge protectors rather than point-of-use. For devices that can't handle a power interruption, you may additionally want a UPS. Phone lines and TV coax should also be protected. And don't bother trying to tell the power/phone/cable company it's their job to protect you from any of this. They can show you in the fine print that it's not.