Power
Line Surges Questions & Answers
Power Lines
QUESTION:
Experts say that power line surge suppressors can actually cause damage to motherboards and data cards, and scramble data sent to interconnected computers, printers and modems. How does this happen, and how can I avoid these problems?
ANSWER:
There are basically two types of power line surge technology, newly patented Series Mode and the older Shunt Mode (so-called hybrids are usually Shunt Mode). The Shunt Mode technology was developed over twenty years ago to protect stand-alone equipment, but this older technology is no longer suitable for modern sensitive interconnected equipment.
Shunt Mode suppressors are still very common because this older technology is inexpensive to manufacture with high profit margins, and as long as people can be seduced by the low prices, these products will continue to be sold. They generally divert power line surges to the safety ground wire, using circuits described as "All Three Modes of Protection". The resulting surges diverted to the ground wire can exceed 1000 volts, exposing sensitive motherboards and data boards to surge disruption, degradation and damage.
This surge voltage on the ground wire varies along the length of the wire. When equipment such as modems, printers and other computers is interconnected, the interconnecting cable creates a "ground loop". If the surge induced on the safety ground wire of one computer is 1000 volts and the surge induced on the safety ground wire at another location is 600 volts, then the difference of 400 volts is fed into the interconnecting cables causing the disruption, degradation, or damage.
While large surges will cause damage, small surges can result in data problems such as lock-ups, data errors, and "mysterious problems".
It is better to avoid Shunt Mode surge suppressors that claim "All Three Modes of Suppression" than to try and live with the problems they cause when they divert surges to the ground wire.
QUESTION:
If Shunt Mode "All three Modes" suppressors can actually cause data problems, what should I look for in a powerline surge suppressor?
ANSWER:
Experts recommend the Series Mode type for modern computing systems, or any sensitive electronic system that may be interconnected with other electronic systems. A heavy duty surge reactor acts to deflect surges rather than diverting surges where they can do further harm.
The following list of specifications should be carefully examined and compared:
- Let-through voltage at maximum rated surge (not simply clamping level, which is the onset of clamping) using standard test pulses. (Let-through voltage is the amount of the surge voltage that is let-through to your protected equipment and should be as low as possible. 180 volts is the theoretical lower limit for 120 volt power lines).
- Service life for various surge levels (including maximum rated surge). A service life of 200 minimum worst-case surges is recommended for a five year life in high exposure locations.
- Filter response. (i.e. greater than 30 dB at 100 kHz.) The important frequency range for surges is 5 kHz to 500 kHz. Greater than 20 dB at 100 kHz is desirable.
- Safety Ground Wire contamination should be avoided if equipment is to be interconnected. Suppressors that claim "all three modes of protection" divert surges to the Safety Ground Wire and should not be used with interconnected equipment.
- Self-test or failure indication (not "protection working" indicators which are often little more than power applied indicators).
QUESTION:
What causes power line surges?
ANSWER:
Surges can be classified as external and internal. External surges are generally more severe than internal surges while internal surges generally occur more frequently (about 80% of all surges are internal). External surges are frequently caused by storms and normal power company switching operations. Internal surges occur when equipment within the building is cycling on and off.
QUESTION:
I have a "Whole building" protector, am I adequately protected?
ANSWER:
A "Whole building" protector generally means protection at the power line service entrance. While this will minimize problems from the 20% or so surges originating outside a building, you still need protection from the 80% or so surges originating within the building.
QUESTION:
How often do surges occur?
ANSWER:
Very large surges occur infrequently (from a few times a year in medium exposure areas to 40 times a year in high exposure areas) since they are mainly storm induced (lightning and temporary interruptions due to storm damage), but surges over 1000 volts may occur many times a day since they are caused by normal equipment operation.
QUESTION:
How large can power line surges get?
ANSWER:
According to industry standards, power line surges inside a building can be up to 6,000 volts, and 3,000 amperes, and deliver up to 90 joules of energy.
QUESTION:
Why are power line surges getting worse?
ANSWER:
Surge problems appear to be worsening because of the increased use of electronics. As the tiny integrated circuits used in electronics proliferate, more of them are exposed to the dangers of power line surges.
QUESTION:
What types of problems do surges cause?
ANSWER:
Problems can range from "soft" errors where information is scrambled in computing systems to gradual circuit deterioration resulting in premature failure and intermittent operation to outright destruction of circuits.
QUESTION:
Does surge induced damage occur all at once or over a period of time?
ANSWER:
Both ways, depending on the circumstances... A violent electrical storm can induce enough surge energy into power lines to destroy your computer in an instant, if left improperly protected. Smaller, internally generated surges can, over time, "wear out" delicate circuits, causing intermittent problems, and slowing down the operation of a system.
QUESTION:
Why don't manufacturers build better surge protection into their equipment?
ANSWER:
For best performance, a surge suppressor must be close to, but not within the protected equipment, since surges may involve very high voltages and currents. These high currents can readily couple into sensitive circuits. Most manufacturers recognize this and provide only minimal internal protection.
QUESTION:
My equipment has a dedicated power line. Do I need a surge suppressor?
ANSWER:
Yes. A dedicated line can minimize internal surge damage, but provides a direct pipeline for the more dangerous external surges.
QUESTION:
How long do surge suppressors last?
ANSWER:
Some surge suppressors fail after a single large surge (the largest surge you should expect in a 120 volt power line within a building is 6,000 volts and 3,000 amperes, according to industry guidelines). Some surge suppressors fail in thermal runaway, can overheat and cause fires.
Before buying a suppressor, compare rated service life for various surge levels. Do not purchase a surge suppressor unless it has a stated service life that is reasonable for your application. According to the industry guide IEEE 587, a medium exposure location could have, on average, one 6,000 volt surge per year. A high exposure location may have 40 6,000 volt surges per year. If you think you are in a high exposure location, and expect a five year life from your surge suppressor, it should be designed to withstand at least 200 6,000 volt, 3000 ampere surges.
QUESTION:
What does the joule rating of a shunt suppressor mean?
ANSWER:
The joule rating is a limitation of the product. Shunt suppressors should not be subjected to surges larger than their joule rating or they will likely fail. Unfortunately, you have no way of knowing in advance how many joules will be in a surge!
QUESTION:
My surge suppressor says it meets IEEE-587 specification. Does this mean it is good?
ANSWER:
IEEE-587 specifies test conditions, not performance. Any inexpensive extension cord can claim to meet IEEE-587. It is the detailed results of the testing to the IEEE-587 standard that is important, not the fact it has been tested.
QUESTION:
Don't all power line suppressors divert surges to safety ground wire?
ANSWER:
NO. Properly designed Series Mode suppressors limit not only surge voltage, but surge current, thus avoiding the problems of neutral wire (common mode) and ground contamination.
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