Lightning surges, occur when a lightning bolt strikes between a cloud and objects on earth. The effect can be direct -injection of the lightning current into the object, or indirect -inducing a voltage into electrical circuits.
We will look at ways of protecting your appliances against lightning surges that come by way of the wires -power, telephone, cable, etc. Protection of the house against the direct effects of lightning is done by properly grounded ...to Mother's lightning rods, a job to be done by gentle touch professionals*. Note also that lightning rods are intended to protect the structure of the house and avoid fires. They do not prevent surges from happening in the wiring.
Direct lightning effects are limited to the object being struck and its surroundings, so that the occurrence is considered rare but it is nearly always deadly for persons or for trees. Well-protected electrical systems can survive a direct strike, perhaps with some momentary disturbances from which they recover (blinking lights and computers restarting during a lightning storm). The key word, of course, is "well-protected" and that is why this booklet is offered to help your home have a well- protected electrical system.
Indirect lightning effects are less dramatic than from a direct strike, but they reach further out, either by radiating around the strike, or by propagating along power lines, telephone system and cable TV. From the point of view of the home dweller, unwanted opening of the garage door, or a surge coming from the power company during a lightning storm, would be seen as indirect effects.
Switching surges occur when electrical loads are turned on or off (by "Mother's gentle touch" or by some appliance controls) within your home, as well as by the normal operations of the power company. An analogy often given is the "water hammer" that can occur in your piping if a faucet is turned off too quickly: the electric current flowing in the wires tries to flow for a short time after the switch has been opened, producing a surge in the wiring, just like the surge of pressure in the piping.
How often, how far, how severe?
So, surges can and do happen!
These questions -how often do surges occur, how far do they travel before hitting your appliances, how severe are they - must be answered, as well as possible, so that you can proceed to the next step of taking calculated risks or making a reasonable investment by purchasing some additional protection. There are several ways of getting surge protection, from the simple purchase of a plug-in device from an electronic store (more on that later) to the installation of protective devices for the whole house, to be done by an electrician or the power company.
You are probably best placed to answer that question if you have lived in your neighborhood for several years. Lightning is random but can strike more than one time at the same place. There are now sophisticated means to record the occurrence of individual lightning strikes; electric utilities and businesses seek the data to make decisions on the risks and needs for investing in protection schemes. The reason for mentioning "several years in your neighborhood" is that the frequency of lightning strikes varies over the years and the section of the country where you live.
How far, how severe?
The answers to these two questions are linked: a nearby lightning strike has more severe consequences than an equal strike occurring farther away. There is also a wide range in the severity of the strike itself, with the very severe or very mild being rare, the majority being in mid-range (a current of about 20,000 amperes for a short time) -but still much shorter than the blink of an eye.
The trade off:
A large stack of dollar bills and some change to replace your unprotected computer, if and when a lightning or some other surge destroyed it...
...or use a small number of bills to purchase a "surge protector" for peace of mind and effective protection.
If you look at it from that point of view, the choice is probably easy and, most likely, you will be looking for one of those "surge protectors" -or some device with a similar name to do the same job.