Surges Happen! How to Protect the Appliances in Your Home - Part 2 of 2 National Institute of Standards and Technology
Technology Administration
U.S. Department of Commerce
NIST recommended practice guide
Special Publication 960-6 Questions . . . and answers Among the questions often asked by consumers about surges, here is a selection of typical concerns and simple answers. Q -When looking at the devices offered in the store, the packages show specifications and claims that puzzle me. Can you explain? A's - Here are some typical specifications, and corresponding comments: Joules -A (simplified) measure of the surge energy that the protector can dissipate without damage to itself. The higher the value, the more energy the protector can handle. Typical values range from about 100 joules, up to 1000 joules or more. Because this joule number is often based on the three combinations of the wiring, many specifications show the total joules rather than a breakdown among each of the three combinations. Maximum surge current (below) may give better information. Clamping voltage -A measure of the voltage-limiting capability of the protector. An oversimplified perception might be that the lower, the better. Many specifications show 330 volts for this voltage. This number is embedded in the UL standard values, but it is not a requirement. Somewhat higher clamping voltages, such as 400 volts or more, may be sufficient for protecting electronic appliances, and will make the surge protector itself less susceptible to damage from "swells". Maximum surge current -A measure of the ability of the protector to handle surge current without damage to itself. You will find a range of values from several hundred to several thousand amperes. Even the lower values offered by manufacturers are sufficient for most surges, but a higher value will give you (generally for a slightly higher price) a comfortable margin of peace of mind. Speed of response -This specification appears on some packages, others do not even mention it. Since practically all protectors use the same kind of technology for the protective components, and their speed of response is inherently adequate for power- line surges, there is no need to emphasize a fast speed of response. Internal protection -Some packages provide a description of what happens on the load side of the surge protector (cut-off or still powered), should the protective element be damaged by an exceptionally large surge or a long overvoltage. See your choice, "Quit and be protected or continue" -but now unprotected. Some packages also provide a cut-off and reset feature in cases of large swells, protecting the protector itself as well as the load. Indicating lights -See the discussion of their meaning on page 7. Be sure that you will remember the meaning after you have discarded the package. If a card with explanations is included in the package, save it because the meaning of the light - on or off, and what the difference there is among colors -is not always clear on the device itself. If the protector maintains power on the load side, how often will you look under or behind your desk to check and make sure that the "Protection on" light is still on ? UL 1449 Second Edition -Some packages show "UL listed Second Edition" rather than the simple "UL Listed" found on others. It shows explicitly that the product has passed the most recent, improved tests for safety. Other standard symbols such as ETL or CSA might be present instead of UL. They all represent the latest testing for safety. Guaranteed protection -A measure of the manufacturer's confidence in the actual performance of the product. As for all guarantees, do read the fine print. Q -If I install one plug-in surge protector in one room, are the receptacles in other rooms also protected? A -Yes, but only to some degree. The wiring in your house is split into several "branch circuits" originating from your service entrance panel. If a surge protector is installed on a particular branch circuit, the other receptacles on the same branch circuit might benefit from it, but that benefit is much less on other branch circuits. To be more relaxed about protection in other rooms, it would be a good idea to install a surge protector for each of the sensitive appliances in the house. This is especially true for the multi-link appliances because of the problem explained on page 12. (See the next Q&A on whole-house protection and Figure 3 on page 19.) Q -Will a surge protector installed at the service entrance be sufficient for the whole house? A -There are two answers to that question: Yes for one-link appliances, No for two-link appliances. Since most homes today have some kind of two-link appliances, the prudent answer to the question would be No -but that does not mean that a surge protector installed at the service entrance is useless. An important function of the service-entrance protector is to divert large surges coming on the power line, before they enter the house. A service-entrance surge protector makes the protection by plug-in protectors easier but, as discussed on page 8, installation at the service entrance generally requires an electrician, unless you are a do-it-yourself person and your city code allows it. Q -Why single out two-link appliances as requiring special protection? A -A first answer to that question is given on page 12, explaining the voltage difference problem for these two-link appliances. A more technical explanation is also given on page 18, intended for your electrician. Q -I have heard about surge protectors degrading over time: What about it ? A -Many, if not all, electronic components will age and have a limited life. The question is really how long a useful life can a surge protector have. Today's well- designed surge protectors might reach their end of life prematurely if exposed to some exceptionally high and rare stress but, for those tested according to UL 1449 Second Edition, the way they fail should not be a hazard. The prevailing opinion among specialists on surge protection is that most of the observed (and quite rare) catastrophic failures of surge protectors are caused by excessively high line voltage that can occur when there is a fault on the power system. Failure from very large surges that might exceed the surge-handling capability of the protector is less likely than failure from high line voltage. And now, the "bottom line" question: Q -How much money should I spend on surge protection? A -It depends on too many factors to give a simple answer. Technology can change, additional features beyond basic surge protection vary, stores offer "specials", and how much margin makes you feel comfortable is an intangible factor. This booklet is not oriented toward rating product performance or prices, but rather toward explaining the principles, so that you can make an informed decision that will give you confidence. Installation hints As discussed earlier, there are several locations in your power system where you can connect (install) a surge protector, depending on the type of protection you desire and your inclination toward do-it-yourself or hire someone. These possible locations are shown in the sketch below, with appropriate hints on how to go about the installation. A very important point to keep in mind is that your surge protector will work by diverting the surges to ground (see "What's in a name") The best surge protector in the world can be useless if grounding is not done properly.  - Meter-base adapter
This is the most involved installation, requiring cooperation of the power company if they allow it to be done by a licensed electrician. They might also do it as part of their own program *. - Service panel, upstream
Also a job for a licensed electrician since the power cannot be turned off on this side of the service panel * **. - Service (breaker) panel, snap-in
First opportunity as a do-it-yourself project, provided that the hardware is compatible and that local authorities allow the owner to do it. - Service panel, downstream
Another possibility for do-it-yourself. The protector should be connected on the load side of a pair of dedicated (spare) breakers in the panel **. - Receptacle, built-in
Provides same protection as a simple plug-in protector, but stays in place and cannot easily be moved to another receptacle, should that become desirable. - Plug-in (with cord or directly into receptacle)
The easiest of all for anyone to do. The only question is "Which to choose ?"; have given you some elements for making that choice.
* It would be a good idea, to ensure compatibility, to ask the electrician to look into the ratings of the device and the power system available fault current. ** The protector should be located close to the service panel (less than about 30 cm or one foot), otherwise the voltage-limiting effect will be degraded. FOR YOUR CONTRACTOR'S EYES ONLY
(But it's OK to take a peek) The problem of shifting reference potentials According to insurance company statistics, two kinds of appliances are at the top of the list as the most frequently damaged during a lightning storm: video systems (receivers and/or VCRs) and computers with a modem connection. There is at least one explanation for that very unhappy situation: if one of the two systems -power or communications -brings a surge to the house, the intended operation of surge protectors creates a difference in the potentials of the references across the two input connections of the appliance, causing failure. In the set-up of Figure 1, a personal computer (PC) is connected to both the power system and the telephone system, and we assume that a surge is coming along the telephone wires. The surge current ("Surge I" in the figure) flows from the telephone system toward the common grounding point via the network protective device (NID) at the point of entry, and the grounding conductor mandated by the National Electrical Code (NEC ®). This current produces a magnetic field that couples into the loop formed by the power branch circuit, the telephone premises wiring lines to the PC, and the bonding conductors. A voltage (Vdiff) is induced in the loop and appears across the power input and telephone input of the PC, with upsetting or damaging consequences. The presence or absence of surge protection on the AC side (Arrester or SPD) has no effect on the coupling. One effective solution is to have the consumer install a combined protector.  | Figure 1
Shifting of reference potentials between power and telephone |
Even though this installation complies with the NEC, the situation is made worse if the point of entry for power and the point of entry for communications are at opposite ends of the house, with a large loop separating the two cables. The 1999 NEC now limits the separation between points of entry to 20 feet (7 meters) for new installations. The situation is even worse yet when the incoming service, cable TV in particular is not bonded to the power service ground. That is a clear violation of the NEC but experience has shown that it is not so rare, and the result can be severe damage to the appliance. NEC© is a registered trade mark of the National Fire Protection Association FOR YOUR CONTRACTOR Recommended integrated bonding The recommended bonding arrangement shown in Figure 2 is applicable for new construction or for existing homes where an opportunity occurs to relocate the point of entry of the cable TV or the telephone NID. It is compliant with the NEC minimum requirements for safety, and will reduce the problem of shifting reference potentials just described by inter-system bonding of all utilities serving a residence. The usual components for each service connection are simply installed next to each other. Another possibility for reducing the shift in reference potentials is to install an integrated, multi-utility surge protection at the breaker panel, as shown in Figure 3. This device includes appropriate surge protection for all three services: AC power, telephone, and cable TV, with the minimum length for the bonding arrangement. Figure 2
Recommended Inter-system bonding |  | Figure 3
Integrated multi-protection device for service panel installation |  |
WHERE TO GET MORE HELP There are many sources of information on surge protection, including codes, standards, handbooks, and many technical papers. Most of these are written for technically-oriented people rather than typical consumers, with the exceptions of the bill-stutters from your utility, occasional consumer-oriented articles, or the present booklet. On the other hand, with the popular and ever-increasing use of the Internet, useful information can be obtained on line. The sources identified below are listed as a starting point for a Web search, but with the understanding that new ones can appear and existing ones can disappear. Furthermore, these sources include some commercial entities as well as non-profit organizations. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that these sources are necessarily the best available for the purpose. Weather and lightning information: http://www.accuweather.com/wx/services
http://www.lightningstorm.com
http://www.lightningsafety.com
http://www.nfpa.org Surge-protective devices http://www.nema.org Wiring practices www.nfpa.org/nec/nechome.asp Power quality (Surges, sags, and outages)
http://www.epri-peac.com NEC© is a registered trade mark of the National Fire Protection Association | 
