Power pollution protection.
Semiconductor manufacturers claim their devices should last nearly 2,000 years. The end user with a computer containing several rows of boards covered with these devices has not had that kind of luck. Why? They are dealing with power--the unknown factor.
No matter where you operate electronic equipment, there will be an electrical grid. Plugging any piece of electronics directly into the commercial AC power system means connecting it into all kinds of transient noise, such as spikes, surges, notches, and other electrical disturbances. You should call it what it is--power pollution. This pollution downgrades the performance and shortens the life of any electronic system exposed to it.
What do computers and computer-driven security equipment have to do with you, a security professional? Everything. It is your job to assist in maintaining positive and effective mission accomplishment. Part of that job involves keeping management informed of known mission-limiting problems.
Consider this example: A few years ago Circuit Court Judge Robert S. Vance of the 11th Federal Circuit Court of Appeals Clerk's Office in Atlanta, Georgia, was murdered in his kitchen when he opened a package containing a pipe bomb. Two days later a package containing the same type of bomb addressed to the clerk was detected in the X-ray machine by a court security officer.
The next morning the machine was crippled by a 2,000-volt spike, which is an impulse that causes a spontaneous increase in voltage. The technician had to replace almost every board in the X-ray machine. Some agencies have plenty of repair money but little or no funding for new purchases. When the work was done, the court had a machine that was as good as new, along with a power conditioner and an uninterrupted power supply (UPS)--plus a $14,000 bill. Not bad for a $20,000 machine.
Power line noise is a natural by-product of electricity. If the demand for power increases beyond the capacity of the electric company's generator in one area or if heavy industry overloads the system, the corrective action taken by the company can cause power fluctuations, called spikes and transients, to appear on the power line. This process is known as notching or grid switching.
The electric companies try to carry it off smoothly, but it usually results in a notch, a brief drop in power, followed by a brief surge as normal power is restored. There is also the power faction connection, a process of switching capacitor banks in and out to compensate for heavy industrial loads. This causes a brief burst of electrical noise.
Lightning strikes are not the most common source of power line noise, but they are the most devastating. Mark Twain once noted that thunder got all of the credit, while lightning did all of the work. Even when the strike is miles away, surges and spikes measuring thousands of volts may show up at electrical receptacles.
As dramatic as lightning is, far more electrical noise is created on a daily basis in buildings and homes by noisy electrical loads. Fluorescent lights, copiers, electric typewriters, heating, ventilating and air conditioning, coffee makers, power tools, arc welders, vending machines, and the like generate noise that goes back into the electrical system as they operate.
All electrical loads make some noise, at least when they are turned on and off. The noisiest are those that have high peak current demands; those that have inductive components, such as electric motors or solenoids (a live wire coil that magnetically attracts a sliding iron core); and especially those that use solid-state switching devices, such as those found in thermostats and light dimmers.
Computerized systems with their peripherals are frequently a part of the problem, not just victims of it. Computer monitors, disk drives, and printers, for example, have large start-up current requirements that can cause transients to travel to and from the peripherals.
Why are today's systems so much more sensitive than they used to be? During the past ten years most computer manufacturers have changed from using linear DC power supplies to modern switch-mode or switching power supplies. The switching power supplies are lighter, smaller, more efficient, and insensitive to changes in power line voltage. However, since they operate by switching on and off rapidly and drawing a lot of current during each cycle, they can generate a lot of noise if they are not connected to a low-impedance power source. Inadequate wiring or some other high-impedance power source is usually the problem.
The other big problem is that chips are more vulnerable to noise than they used to be. In each new generation more and more transistors are packed into the same microscopic space. And as the individual transistors get smaller and smaller, the amount of electrical overstress they can survive gets lower and lower. Modern semiconductor devices can now be disrupted by as little as 1/2 volt of noise. More than 10 volts of noise starts to destroy them.
Power line noise enters a computer from two sources--normal mode and common mode. Normal mode refers to activity involving line (hot) and neutral conductors (wires). Common mode refers to activity involving neutral and ground conductors. Some electrical engineers describe common mode as between line and neutral and ground. Neutral is the white or gray wire. In modern electrical receptacles, two slotted openings and a rounded opening appear below the slots. The longer of the two slots is the neutral slot.
Line or hot is normally the black wire in home wiring. That is the one attached to the circuit breaker or fuse. It can also be black, red, blue, brown, or yellow. Ground is either the plain copper or green colored wire. It acts as a safety in the circuit. Today's solid-state electrical appliances use ground as a logic reference point. That wire has been required in all new construction and renovation since 1964.
Computers are better protected against normal mode noise than they are against common mode noise. Normal mode noise has to pass through the system's power supply where at least some of it will be filtered out before it reaches the circuit boards. In addition, the AC electrical system was designed to protect itself and its loads against normal mode noise. It does this by shorting itself out at the high voltages and high frequencies of power line noise and dumping excess energy to ground. Because of this, most of the normal mode noise is converted into common mode noise.
Common mode noise is harmless to most of the loads that the power system was designed to operate because they only use the ground wire as an alternate path back to ground for safety reasons. Unfortunately, modern computer systems and their peripherals use ground as a reference point and common mode noise is a serious threat to them.
In a typical system, the safety ground is either directly or capacitively coupled to the computer's logic reference ground. If more than a 1/2 volt of noise gets into the ground bus, it will disrupt system operations. This is why a very quiet ground is required for any computerized system.
The vulnerability of computerized systems to power problems is well documented. Studies have shown that up to 80 percent of all computer failures are power related. Removing noise from the electrical environment is one of the most important methods of improving a system's reliability.
How do you remove noise from electrical power? You apply the same principles to electricity that you apply to gasoline, oil, air, or water--filter it, condition it.
There is a lot of confusion about the meaning of the term power conditioning. Power conditioning is confused with other devices, such as surge suppressors, voltage regulators, spike arresters, and electromagnetic interference (EMI) and radio frequency interference (RFI) filters. Most of these devices are designed to treat one or two symptoms of noisy power.
A true power conditioner should protect a system completely from all the effects of power line disturbances. Four leading technologies for industrial power conditioning are isolation transformers, ferroresonant (constant-voltage) regulators, electronic tap-changing regulators, and low-impedance power conditioners.
Four basic power conditioning functions are essential to give a system the total protection it needs:
* Reduce all power line disturbances to levels that are harmless to semiconductors.
* Provide a clean, single-point, all-purpose reference ground for all loads connected to the conditioner.
* Prevent disruptive interaction between noise generating loads connected to the conditioner.
* Provide peak current on demand without sacrificing efficiency or going into a by-pass mode.
Most computerized systems have some level of noise immunity built into them. But the equipment manufacturers cannot predict how well their noise rejection will perform in the field because of the variety of system configurations in the marketplace. Add-ons, accessories, and peripherals all change a system's sensitivity to electrical noise.
Even more unpredictable is the electrical environment in which the equipment will have to perform. Will it be quiet or noisy? What about six months or a year from now? To be effective under all circumstances, a power conditioner must be able to reduce the worst possible electrical noise to levels that are harmless to semiconductors.
The power conditioner must be tested against the largest noise pulse that can possibly appear on building wiring, as described by the Institute of Electrical and Electronics Engineers (IEEE) in 1980, with American National Standards Institute (ANSI)/IEEE C62.41 Category A Ring Wave. It specifies an applied test pulse of 6,000 volts with a rise time of 0.5 microseconds, applied with the power conditioner under load. This simulates the maximum surge created by a nearby lightning hit as experienced within a building's electrical distribution circuits. It is based on the fact that pulses in excess of 6,000 volts will arc over standard spacings or wiring insulation and become ground-neutralized before entering the building's electrical system.
This pulse must be reduced to less than 10 volts of normal mode noise and less than half a volt of common mode noise. The power conditioner must specify this extremely low level for common mode noise because noise on the ground wire is either directly or capacitively coupled to the computer system's logic ground. More than half a volt of noise here will disrupt the system's operations.
A transformer-based power conditioner should be used. Using a transformer allows the neutral ground bond to be safely and legally reestablished at the secondary side of the transformer. In addition, there should be capacitors between line and neutral on the output that tie them together at the high frequencies where noise is found.
By tying line, neutral, and ground together right next to the systems being protected, both normal and common mode noise are practically eliminated. The safety ground passes straight through and is unaffected. The effective power conditioner provides an ideal single-point computer grade ground, if it powers the entire system, including all peripherals, and no other supplementary grounds are used. If it is not practical to power the entire system from the same conditioner, other remotely located power conditioners must be used to preserve the system's integrity.
Peripherals can be a problem, as mentioned earlier, if the noise generated by the printer, for example, finds its way into the computer plugged in right next to it. The problem is made far worse if the computer and printer are both plugged into an older technology power conditioner, such as a ferroresonant or high-isolation type. The older high-output impedance design power conditioner acts like an induction coil, turning low-level switcher noise into higher level noise that travels into everything connected to the conditioner.
One of the characteristics of switch mode power supplies is that they have a high current draw during the portion of each AC cycle when they turn on. Ferroresonant and high-isolation power conditioners cannot meet these peak current demands unless they are considerably oversized for the application or have a current bypass feature. Oversized units operate at lower efficiency, which means higher electric bills due to heat loss. An effective power conditioner is a low impedance design that allows it to provide peak current on demand. An example of impedance would be using a crimped garden hose--the fewer obstructions the better.
The subject of voltage regulation is touted by some power conditioner manufacturers. Switch mode power supplies provide their own voltage regulation, easily handling voltage swings from around 90 to 130 volts. Some people have a careless attitude when it comes to bypass features on some power conditioners. Raw power, they may think, is only used at the beginning of a cycle when peak demand is there. However, harmful spikes can occur at the beginning of a cycle and be expensive to repair or replace.
Power line noise is the cause of the dreaded 3 D's--disruption, degradation, and destruction. Even low-level electrical noise will cause a system to lock up once in a while. The user has to reset or power down the computer to escape this condition, causing the loss of all data in memory. More common than a lockup, is getting one of a variety of error messages on the screen.
Error messages are another concern. Disk drives are particularly sensitive to noisy power. Communications between the computer and its peripherals are also vulnerable to noise, particularly if they are placed some distance away.
A garbled printout, for example, is a common symptom of power problems. Some noise glitches will not cause the computer to crash but will change or erase data in memory. Then, problems like inconsistent results, erroneous calculations, lost or changed letters or words, missing paragraphs, and missing files occur.
After being exposed for a long time to low-level noise or after a catastrophic event like a lightning strike, some or all of the hardware will fail completely. Even after you repair all the damage, there will probably be additional failures for months.
Several critical items must be examined when looking for suspected problems at the site. Good grounding is essential if power-related problems are to be minimized. Were adequate electrical receptacles used and correctly wired and wired with the correct polarity?
Incorrectly wired AC receptacles are fairly common. Connecting a computerized system to them will severely downgrade performance. If they are polarity sensitive, serious damage can be done. Inspect to see that all the receptacles used are of the industrial grade type?
Loose contacts are a source of arcing, which is another form of high-frequency noise. Were the back-wiring ports used? The use of the back-wiring port provides more surface contact between the conductor and the receptacle. This improves electrical conductivity because the conductor is held in place on all sides by full surface clamps. Conventional side wiring provides contact between the binding posts and the metal contact plate, and therefore, reduced conductivity.
All binding posts and terminal screws should be tightened until full contact is made with the contact plate and then tightened an additional pound-foot.
Is there a continuous copper ground wire all the way back to the ground bus in the service entry panel or to the secondary side of the transformer serving that portion of the building? It is not unusual to find the conduit used as the ground conductor in outlet boxes. This type of grounding is unacceptable.
Do not be surprised to find that the ground and neutral conductors have been tied together at the outlet box or distribution subpanel. In addition to degrading the quality of the ground, this is a clear violation of the National Electrical Code (NEC) and may result in both a shock and fire hazard in the building. The only places that ground and neutral may be legally and safely joined are at the building's electrical service entrance panel, at the secondary side of the transformer serving that portion of the building, or at the secondary side of a transformer-based power conditioner.
The branch circuit serving the computer should have only other technical loads on it. The copy machine, soft drink machine, coffee pot, and water cooler are not considered technical loads.
The specific technique for installing an isolated ground circuit is not described in the NEC. Therefore, no official guidelines exist for electricians and electrical engineers.
Over time, even the best designed isolated ground circuit systems become corrupted by nontechnical loads, remodeling, or other electrical work that often taps in anywhere. Many isolated ground circuits appear even noisier than standard branch circuits because there are fewer loads on each circuit.
Of all the ideals sought by the dedicated isolated ground circuit methodology, the only consistent advantage is lessening the chance of creating chronic voltage sags because of circuit overload. But this can be accomplished without the added confusion of isolated ground connections. Properly installed standard technical circuits accomplish the same objectives and will do as much as isolated ground circuits toward eliminating the problem of different ground potentials.
A comprehensive evaluation of the system should be conducted. The best approach is to have a full-range power monitor plugged into the wall receptacle to monitor conditions for a week.
The analysis will pinpoint the problems as they occurred and recommend corrective action. If short-term power outages or low-voltage conditions occurred, then a UPS may be required. The report may determine that grounding must be improved.
These tests should be completed before any improvements are undertaken. Power conditioning can accomplish a great deal, but it will not work to its maximum potential without good low-resistive grounding.
The average cost for the power survey, staffing, and equipment, is $3,000, plus or minus 10 percent. The average cost of the grounding survey, staffing, and equipment, is $2,000, plus or minus 10 percent.
But how much will it cost to reboot, reconstruct, reenter, and reverify the correctness of the data? You might be able to defer costs of the grounding survey until after you have installed the necessary power conditioning.
If you have added a lot of computer equipment and the electrical system was not designed with modern computers in mind, you may want to consider oversizing the neutral returns to compensate for the effects of additive harmonics in the neutral conductors.
Pick the right piece of equipment for the specific job. All of the system's peripherals must be conditioned along with the computer itself.
Computers and other electronics are increasingly integral to the functioning of any business, and the security industry must be prepared to address the related security concerns.
Special thanks to Herb Goldstein of ONEAC Corporation for his encouragement and technical support for his article.
William J. Warnock is president of Warnock Security Solutions, Inc., in Haymarket, Virginia. He is a member of ASIS.
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|Title Annotation:||Computer Security|
|Author:||Warnock, William J.|
|Date:||May 1, 1993|
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