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Not just power-line surges
Among other disturbances on the power lines, there was a brief mention of sags and outages. You are certainly and unhappily well- acquainted with outages that can occur for any number of reasons beyond the control of your utility. Sags -a brief decrease of the line voltage -can be more subtle and do occur more often than the complete outage. You will notice these when the lights dim momentarily, digital clocks or VCR controls blink, or your computer shuts down then reboots -possibly losing some data.
Industrial and commercial users, health-care facilities and other critical systems have for many years used a device called "uninterruptible power supply" (UPS) that provides continuous power across a sag, or for the first portion of an extended outage (an independent local power generator set can then kick in).
The aggravation of consumers caused by sags and outages has created a mass-market for consumer applications, making them affordable when looked at as protection against these annoying (but not damaging) disturbances -and with built-in surge protection as a bonus in many cases. These consumer-type UPSs have a small battery which is sufficient to ride through any sag and short outages. Some models even include the software to make a computer shut down in an orderly sequence in case of a long outage.
Surges in other systems
So far, we have looked at surges on the power line alone, or on a combination of power and communications lines. Surges of a slightly different kind can also happen in parts of other electrical systems that do not directly involve a power line. Examples of these are: the antenna for a remote garage door opener, the sensor wiring for an intrusion alarm system, the video signal part of a satellite dish receiver. Surges in these systems are caused by nearby lightning strikes.
These other systems just mentioned have not been the subject of standards on surge protection as much as power and telephone systems. Furthermore, protective devices for these other systems are not as readily available to consumers. It is more difficult to offer well-defined guidance on surge protection for these systems. Applying preventive surge protection schemes to an existing system might be difficult when the sensitivity of such a system to surges is not known. When considering installation of a new system, it would be a good idea to ask pointed questions on that subject before signing the contract.
Protection for other systems
Some codes or practices aimed at providing safety for persons, when they are correctly applied, can also provide some equipment protection.
For instance, the general practice of telephone companies is to provide a surge protector as part of their services at the point where the telephone line enters the house (in dense urban environments, the National Electrical Code allows an exception). This protector is known as the "Network Interface Device" (NID) and you will find it on the outside of your house.
Another example of code requirement is that of cable TV systems for which the National Electrical Code requires proper safety-oriented grounding practices. The problem, however, is that in some cases, the video equipment can still be damaged by voltage differences.
With the increasing popularity of small-dish satellite receivers, installation by the user as do-it-yourself has also increased. Typical instructions for installation show how to make the connections, for instance in the figure at right. What the figure does not show is the need to provide a combined protector for power, telephone, and cable.
A well pump installed outside the house presents a double challenge: protection the pump motor itself against surges, and protection the house wiring against surges that might enter the house by the line that powers the pump. The first protection is generally built-in for modern submersible pumps. The second protection should be provided by surge protector installed at the point where the power line to the pump leaves the house, using protectors similar to those applied at the power lin service entrance.
Intruder alarm systems using wires between sensors and their central control unit can be disturbed -and damaged in severe cases -by lightning striking close to the house. The wires necessary for this type of installation extend to all points of the house and act as an antenna system that collects energy from the field generated by the lightning strike, and protection should be included in the design of the system, rather than added later by the owner. Wireless systems are less sensitive than wired systems.
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