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A reliable supply of electricity is a necessity for the operation of your business. Sometimes outages are inevitable and can be costly. The definitions below describe standard electrical terms, sources, problems and suggestions to protect against interruptions. |
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Power failures, also known as “blackouts”, are the easiest power problem to diagnose. If the lights go out, chances are there has been a power failure. Any temporary, or not so temporary, interruption in the flow of electricity will result in a power failure, which can cause hardware damage and data loss.
Violent weather is the first thing that comes to mind, but there is any number of other causes. Overburdened power grids, car accidents that bring down power lines, lightning strikes, and human error are all likely sources.
Power failures are inconvenient and annoying. They can cause computer users to lose hours of work when systems shut down without warning. Power failures can even damage hard drives resulting in loss of all data on a system. Consider the fact that a single power outage on a high traffic network can stall hundreds of users, and the seriousness of power failures becomes evident. Even worse, when the power returns, it often brings after-blackout spikes and surges to cause even more damage.
Computer users should consider a UPS system to protect their systems. These systems monitor line levels and switch over to battery power when utility power fails.
“Brownouts” are periods of low voltage in utility lines that can cause lights to dim and equipment to fail. Also known as, “voltage sags”; this is the most common power problem, accounting for up to 87 percent of all power disturbances.
Recent statistics show that the U.S. population tries to pull an average of 5 percent more than the utility companies can provide. The demand for power is rapidly increasing, but the supply of power is not. Damage to electrical lines and other factors can cause utility brownouts. Locally, equipment that draws massive amounts of power such as motors, air conditioners, etc., can cause momentary brownouts to occur. Under voltages are often followed by “voltage spikes" which are damaging to computer components and data.
Voltage variation can be the most damaging power problem to threaten equipment. All electronic devices expect to receive a steady voltage (120 VAC in North America) in order to operate correctly. Brownouts place undue strain on power supplies and other internal components, forcing them to work harder in order to function. Extended brownouts can destroy electrical components and cause data glitches and hardware failure.
Surge suppressors do only half the job with the balance done by line conditioners and Uninterruptible Power Supplies (UPS), which provide the best defense against voltage problems. They regulate both over and under voltages while line conditioners provide three separate levels of voltage correction.
Adjusting computer-grade AC power-consuming equipment in meeting ANSI C84.1 specifications provides improved protection against brownouts.
Throughout the sphere of Power Quality, you will hear the terms "spike", "transient", and "dip/sag/surge/swell". These three categories are very real and refer to loosely defined boundaries based on time or duration of the event.
However, there is one thing that timing does not take into account and that is the energy released during such an event. Energy usually is being measured in joules. Although watt-seconds (Ws) is relative to Joules (J), watts require that you know both the voltage and the current, the latter not always being available.
In the early 1980's, the Computer and Business Equipment Manufacturers Association (CBEMA, and now the ITI Council) established a susceptibility profile curve to aid manufacturers in the design of power supply protection circuits. This curve has become a standard reference within the industry.
The CBEMA guideline is a realistic, at-the-equipment, maximum allowable voltage that equipment can withstand, without damage or upset. Computer power quality is described by the CBEMA curve. The curve describes specifications for power supplies used in computers. If voltage is above the curve, then there will be an over-voltage condition, which can damage the power supply. If the voltage is below the curve, then the computer may turn off for lack of voltage to the power supply.
The Federal Information Processing Standards (FIPS) publication, "Guidelines on Electrical Power for Automatic Data Processing Installations" (FIPS Pub. DU294) includes a susceptibility profile that is considered a typical design objective for computer hardware designers. The profile shows the relationship between clamp voltage, system voltage and surge duration.
The CBEMA standard essentially defines the threshold computer-based equipment is designed to be able to withstand for short duration, less than 200 microseconds, and transient voltages, if these voltages do not exceed a level that is five times the sine wave peak voltage. It effectively encompasses all the factors involved with voltage deviations, from long term through high-speed distortions of the waveform.
Approaching this from an electronics angle, we will notice that the filters consist of inductors and/or capacitors and are arranged as low-pass filters. Low-pass filters attenuate frequencies above their cut-off. The sharper the deviation, the higher the frequency. The higher the frequency, the higher the attenuation. Power Quality is therefore an electronics field, not a power-engineering field.
The goal is to protect electrical and electronic equipment connected to the AC power line, limit transient voltage amplitudes to less than the CBEMA guidelines of 5 x E rms x 1.414 volts, for less than 200 us duration impulses. For commercial power lines, this works out to be:
Line Voltage (rms) Maximum Suppression Voltage
120 VAC 850 V
208 VAC 1470 V
220 VAC 1594 V
240 VAC 1700 V
277 VAC 1956 V
480 VAC 3394 V
600 VAC 4250 V
The CBEMA Standards assert that complex computing equipment will function properly if the transient voltages are limited to less than shown in the above chart.
A network is a collection of electrical signaling circuits, each carrying digital signals between pieces of equipment. There are power sources, conductors, and loads involved in the process. The power source is a network device that transmits an electrical signal. The conductors are the wires that the signal travels over to reach its destination (another network device). The receiver is the load. These items, connected together, make up a complete circuit.
The key to successful signal transmission is when a load receives an electrical signal, the signal must have a voltage level and configuration consistent with what was originally transmitted by the energy source. If the signal has undergone too much corruption, the load will not be able to interpret it accurately.
In the computer world, the electric signal transmitted by an energy source is a digital signal known as a pulse. Pulses are simply the presence of voltage and a lack of the presence of voltage, generated in a sequence. These pulses are used to represent a series of ones and zeroes and ones (the presence of voltage being a 1, and the absence of voltage being a 0). These zeros or ones are called bits. Many years ago, computer engineers began using groupings of eight bits to represent digital "words,” and to this day, a series of 8 bits are called a byte. These terms are used everywhere in the computer field. A good cable will transfer a signal without too much distortion while a bad cable will render a signal useless.
Grounding and wiring problems account for up to 80 percent of all power quality problems, making them the most important consideration for successful operation of sensitive electronic equipment. Wiring and grounding checks are necessary first steps when evaluating power quality problems. Sometimes it may be as simple as tightening a loose connector or replacing a corroded conductor. Proper grounding must be:
- Permanent and continuous
- Have the capacity to conduct safely any fault current imposed on it
- Have sufficient low impedance to limit the voltage to ground and facilitate the operation of the circuit protective devices
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“Harmonics” must be taken seriously. Any distortions in the voltage or current wave cause harmonics. Harmonic currents create heat. This heat over a period of time, will raise the temperature of the neutral conductor causing nuisance tripping of circuit breakers, over-voltage problems, blinking of incandescent lights, computer malfunctions, etc. Electrical devices that cause harmonics are personal computers, dimmers, laser printers, electronic ballast, stereos, radios, televisions, fax machines, and any other equipment powered by switched-mode power supply (SMPS) equipment.
Prevent problems by using a dedicated circuit for electronic equipment. On a branch circuit, use an isolated ground wire for sensitive electronic and computer equipment. A more expensive way is to rectify and filter the mains thus effectively removing all low frequency harmonics including the fundamental. Oversized neutrals are another possible means to prevent overheating of this wire. In power distribution systems electricians are usually interested in measuring the current, thus a "true-RMS" current-measuring clamp-on meter is normally use.
Harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency being 60 Hz. For example, if the fundamental power frequency is 60 Hz, then the 2nd harmonic is 120 Hz; the 3rd is 180 Hz, etc. In modern test equipment today, harmonics can be measured up to the 63rd harmonic. When harmonic frequencies are prevalent, electrical power panels and transformers become mechanically resonant to the magnetic fields generated by higher frequency harmonics. When this happens, the power panel or transformer vibrates and emits a buzzing sound for the different harmonic frequencies. Harmonic frequencies from the 3rd to the 25th are the most common range of frequencies measured in electrical distribution systems.
Harmonics are caused by electronic equipment powered by switched-mode power supply (SMPS) equipment, also referred to as non-linear loads. This type of non-linear load or SMPS equipment generates the very harmonics they are sensitive to and originate right within your building or facility. SMPS equipment typically forms a large portion of the electrical non-linear load in most electrical distribution systems.
There are two types of non-linear loads: single-phase and three-phase. Single-phase non-linear loads are prevalent in modern office buildings while three-phase non-linear loads are widespread in factories and industrial plants.
These non-linear power supplies draw current in high amplitude short pulses. These current pulses create significant distortion in the electrical current and voltage wave shape. This is referred to as a harmonic distortion and is measured in Total Harmonic Distortion (THD). The distortion travels back into the power source and can effect other equipment connected to the same source.
To give an understanding of this, consider a water piping system. Have you ever taken a shower when someone turns on the cold water at the sink? You experience the effect of a pressure drop to the cold water, reducing the flow of cold water. The result is you are burned! Now imagine that someone at a sink alternately turns on and off the cold and hot water. You would effectively be hit with alternating cold and hot water! Therefore, the performance and function of the shower is reduced by other systems. This illustration is similar to an electrical distribution system with non-linear loads generating harmonics.
Harmonics are generally not an issue if you do not have any electronic SMPS equipment or non-linear loads in your building or facility.
In an electrical distribution, system harmonics create:
- Large load currents in the neutral wires of a 3-phase system. Theoretically, the neutral current can be up to the sum of all three phases therefore causing overheating of the neutral wires. Since only the phase wires are protected by circuit breakers or fuses, this can result in a potential fire hazard
- Overheating of standard electrical supply transformers, which shortens the life of a transformer and will eventually destroy it. When a transformer fails, the cost of lost productivity during the emergency repair far exceeds the replacement cost of the transformer itself
- High voltage distortion
- High current distortion and excessive current draw on branch circuits
- High neutral-to-ground voltage often greater than 2 volts
- High voltage and current distortions
- Poor power-factor conditions result in monthly utility penalty fees for major users (factories, manufacturing, and industrial) with a power factor less than 0.9
- Resonance that produces over-current surges. In comparison, this is equivalent to continuous audio feedback through a PA system. This results in destroyed capacitors and their fuses and damaged surge suppressors, which will cause an electrical system shutdown
- False tripping of branch circuit breakers
Protecting Against Harmonics
These are recommended ways to protect against harmful harmonics:
- Use double-size neutral wires or separate neutrals for each phase
- Specify a separate full-size insulated ground wire rather than relying on the conduit alone as a return ground path
- On a branch circuit, use an isolated ground wire for sensitive electronic and computer equipment
- Segregate sensitive electronic and computer loads on separate branch circuits all the way back to the electrical panel
- Run a separate branch circuit for every 10 amps of load
- Install a comprehensive exterior copper ground ring and multiple deep driven ground rods as part of the grounding system to achieve 5 ohms or less resistance to earth ground
- Oversize phase wires to minimize voltage drop on branch circuits
- Shorten the distance on branch circuits from the power panel to minimize voltage drop
Solving Harmonic Problems
Harmonic treatment can be performed by two methods: filtering or cancellation.
- A harmonic filter consists of a capacitor bank and an induction coil. It is designed to trap and suppress analog and electrical spikes on either electrical or telephone lines. All spikes and noise show up in the form of electrical impulses. Clearing out the offending ones can often stabilize the operating conditions of a computer and/or modem.
The filter is designed or tuned to the predetermined non-linear load to filter a predetermined harmonic frequency range. Usually this frequency range only accounts for one harmonic frequency. This application is mostly used when specified for a UPS or variable frequency drive motor in a manufacturing plant.
- Harmonic cancellation is performed with harmonic canceling transformers also known as phase-shifting transformers. A harmonic canceling transformer is a relatively new power quality product for mitigating harmonic problems in electrical distribution systems. This type of transformer has patented built-in electromagnetic technology designed to remove high neutral current and the most harmful harmonics from the 3rd through 21st. The technique used in these transformers is call "low zero phase sequencing and phase shifting". These transformers can be used to treat existing harmonics in buildings or facilities. This same application can be designed into new construction to prevent future harmonics problems.
Identifying the Cause of a Power Quality Problem
Identifying the cause of a power quality problem is often like solving a mystery. A power disturbance log helps to systematically and quickly uncover information. A log needs to include the following:
Times of Occurrence
- Date and time of each electrical disturbance
Equipment Affected
- What equipment was affected, note equipment failures and data loss
Length of Outage
- Document the outage in the following ways, this identifies what type of outage occurred:
- Shorter than two seconds
- Two to 120 seconds
- Longer than two minutes
Weather Conditions
- Note temperature and weather conditions such as wind, rain and lightning
Use the data from the log to identify patterns, consider recent changes in your operation and what is happening in your facility at the time of the problem.
- Addition or changes of electrical equipment
- Work done on the electrical system
- Problem frequency
- Other happenings at the time of the problem
- Large loads switched on
- Lights flickering
- Power outages
- Any other equipment affected
- Is it on the same circuit?
- Does the same manufacturer make it?
Lightning
Lightning is the discharge of static electricity from the atmosphere to the ground. The way this happens is a leader from the atmosphere pulses toward earth seeking out active electrical grounds. While some ground-based objects emit varying degrees of electric activity causing streamers, when a leader connects with a streamer the connection is complete and the current flows toward earth and through the object that created the streamer. These current levels can exceed 400 kA with temperatures up to 50,000 degrees F and speeds approaching one-third the speed of light. It is easy see what kind of damage is possible with forces of this magnitude.
- Lightning current can be carried inside a building by electric power, telephone, analog or digital data lines (e.g., closed circuit television cameras, sensors in an industrial plant, etc.). This direct injection of lightning current inside a building can cause immense damage to electrical – and especially electronic – circuits and equipment.
- The electromagnetic fields from the current in a lightning strike can induce currents and voltage in wire and cables inside a building. Such surge currents are typically less intense than direct injection of current, but can easily vaporize integrated circuits in computers, modems, electronic control circuits, etc.
- Lightning can also be conducted along plumbing pipes and other utility piping such as gas lines.
Line Noise
The term "line noise" refers to random fluctuations—electrical impulses that are carried along with standard AC current. Turning on fluorescent lights, laser printers, working near a radio station, using a power generator, or even working during a lightning storm can all introduce line noise into systems.
Line noise interference can result in many different symptoms depending on the situation. Noise can introduce glitches and errors into programs and files. Hard Drive components can be damaged. Televisions and computer screens can display interference as "static" or "snow," and audio systems experience increased distortion levels.
Eliminating Line Noise
Surge suppressors, line conditioners and UPS units include special noise filters that remove or reduce line noise. The amount of filtration is indicated in the technical specifications for each unit. Noise suppression is stated as decibel level (dB) at a specific frequency (kHz or MHz). The higher the dB, the greater the protection.
Be wary of "surge/noise suppressors" that do not provide this information. Some surge suppressors (Such as the Tripp Lite Isobar suppressors) take noise suppression to a new level with isolated filter banks. These special banks prevent line noise generated from one device from traveling through the surge suppressor to interfere with other equipment.
Using a laser printer (a notorious source for line noise) connected to the same suppressor that powers a computer will not endanger the computer.
“Power quality” is simply the interaction of electrical power with electrical equipment. If electrical equipment operates correctly and reliably without being damaged or stressed, the electrical power is of good quality. On the other hand, if the electrical equipment malfunctions, is unreliable, or is damaged during normal usage, the power quality is poor.
A high degree of Power quality allows loads connected to a power system to operate with greater than 99.999 percent reliability. Without concerted effort, reliability rarely exceeds 99.9 percent. Power quality is limited by events on the transmission and distribution system, as well as events on the user site. Transmission and distribution events include outages, poor feeder stability, lightning strikes, capacitor switching, fault clearing, load changes, etc. User site events include motor starts, noise generating equipment, faulty ground systems and electrical connections, and load switching transients.
Computers, programmable logic controllers (PLCs), power distribution units (PDUs), instrumentation, telecom, and other solid-state systems will operate reliably when applied carefully. However, all these units have one thing in common: They are voltage and time-sensitive. In other words, voltage sags and swells, as well as outages and transients, will seriously affect their operation.
Disturbances associated with powering, grounding and protecting solid-state devices can be measured, analyzed and evaluated using test equipment specifically intended for digital logic systems. These instruments, when located near the suspected disturbance, or when measuring the unusual operation of the power distribution system, will provide data on voltage fluctuations, short and long-term excursions, and the specifics on how the disturbance places the equipment at risk.
As a general statement, any deviation from a normal AC voltage source can be classified as a Power quality issue. Power quality issues can be high-speed events such as voltage impulses/transients, high frequency noise, wave shape faults, voltage swells and sags and total power loss. Power quality issues will affect each type of electrical equipment differently. By analyzing the electrical power and evaluating the equipment or load, it can be determined if a power quality problem exists.
Power quality can be verified by installing a special type of high-speed recording test equipment to monitor the electrical power. This type of test equipment will provide information used in evaluating if the electrical power is of sufficient quality to reliably operate the equipment. Monitoring provides valuable data that needs to be interpreted and applied to the type of equipment being powered.
Examples of Power Quality
- A standard 100-watt light bulb requires 120 volts to produce the designed light output (measured in lumens). If the voltage drops to 108 volts (-10 percent), the light bulb still works but puts out less lumens and is dimmer. If the voltage is removed as during a power outage, the light goes out. Either a low voltage or complete power outage does not damage the light bulb. If however the voltage rises to 130 volts (+10 percent), the light bulb will produce more lumens than it was intended to, causing overheating and stress to the filament wire. The bulb will fail much sooner than its expected design life.
- A CRT or monitor for a personal computer uses a 120 volt AC power supply to convert the incoming voltage to specific DC voltages required to run the monitor. These voltages include 5 VDC for logic circuits and high voltage DC to operate the cathode ray tube (CRT). If the incoming voltage drops to 108 volts (-10 percent), the power supply is designed to draw more current or amps to maintain the proper internal voltages needed to operate the monitor. Because of the higher current draw, the power supply runs hotter and internal components are stressed. Although the operator of the monitor does not notice a problem, the long-term effect of running on low voltage is reduced reliability and increased failures of the monitor. If the power drops below the operating range of the power supply, the monitor will shut down. If the voltage goes above 132 volts AC (+10 percent), the power supply will not be able to regulate the internal voltages and the internal components will be damaged from the high voltage.
Power Quality Problems
Power quality problems have many names and descriptions. Surges, spikes, transients, blackouts, and noise are some common descriptions.
Power quality issues can be divided into short duration, long duration, and continuous categories. The computer industry has developed a qualification standard to categorize power quality events. The most common standard is the CBEMA curve (Computer Business Equipment Manufacturing Association).
Sources of Power Quality Problems
The majority of power quality problems are related to issues within a facility as opposed to the utility. Based on years of experience, 90 percent of power quality problems are caused within a customer’s facility. Typical problems include grounding and bonding problems, code violations and internally generated power disturbances. Other sources of power quality problems include:
- Adjustable speed drives
- Air conditioners and compressors
- Automatic switch opens and closes to protect shorted equipment
- Arc welders
- Battery chargers
- Bird or squirrel makes contact between two conductors
- Car/pole accident
- Circuit breaker switching
- Commercial disturbances
- Copy machines and printers
- Electronic power supplies
- Elevators
- Fluorescent lights with electronic ballasts
- Induction machinery
- Insulator flashover
- Insulator damaged by vandalism
- Lightning strike
- Motor start-ups
- Outage on utility’s interconnected system
- Personal computers
- Silicon-controlled rectifier drives
- Tree damage to wires
- X-ray equipment
- Voltage-sensitive equipment
Other internal issues include powering different equipment from the same power source.
Let us take an example of a laser printer and a personal computer. Most of us would not think twice about plugging the laser printer into the same power strip that runs the PC. We are more concerned about the software and communication compatibility than the power capability; however, some laser printers can generate neutral-ground voltage swells and line-neutral voltage sags every minute or so. The long-term effect to the PC may be power supply failure. We have to be careful in how technology is installed and wired.
Power reliability is the trustworthiness to do what the electric system is designed to do and the percentage it is available for use. Taking into account planned and unplanned downtime. If a system is down an average of four hours out of 100 hours of operation, its AVAIL is 96 percent. |
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Power Reliability Disturbances
“Power Reliability” disturbances can be categorized into the following seven basic groups. |
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- Outage: An outage is a complete loss of power. A temporary outage lasts anywhere from three seconds to one minute. A long-term outage would last longer than one minute. Possible causes include:
- Accidents, acts of nature such as weather, storms, lightning, squirrels, birds and trees getting into power lines, etc., which require the proper operation of utility equipment (like fuses)
- Internal short circuit resulting in the proper operation of a customer's breakers and fuses
- Momentary Outage: A momentary outage is a very short loss of power lasting from 1/120th of a second to three seconds. This is often seen as a "blink" in your lights. Possible causes include:
- Accidents, acts of nature such as weather, storms, lightning, squirrels, birds and trees getting into power lines, etc., which require the proper automatic operation of utility protective equipment
- Undervoltage/Overvoltage: An undervoltage is any long-term change, lasting more than a minute, below normal voltage. An overvoltage is any long-term change, last more than a minute that is above normal voltage. Possible causes include:
- Overloaded wiring or equipment
- Poor voltage control possibly due to large load swings or improper transformer settings
- Voltage drop due to undersized wiring and faulty or poor electrical connections
- Sag/Swell: A sag or swell is any short-term (lasting less than one minute) decrease (sag) or increase (swell) in voltage. Voltage sags are caused by abrupt increases in loads such as short circuits or faults, motors starting, electric heaters turning on, or they can be caused by abrupt increases in source impedance, typically caused by a loose connection. Voltage swells are brief increases in voltage over the same time range. Voltage swells are usually caused by an abrupt reduction in load on a circuit with a poor or damaged voltage regulator, although they can also be caused by a damaged or loose neutral connection. Possible causes include:
- Major equipment start-up or shutdown
- Short circuits
- Improper electrical connections
- Sudden load reduction
- Surge/Transient: A surge or transient is a sudden change in voltage up to several thousand volts lasting a few microseconds (a microsecond is one millionth of a second). Possible causes include:
- Lightning
- Proper operation of utility fuses, reclosers and breakers
- Turning on or off large equipment
- Operation of welding equipment
- Noise: Noise is an unwanted electrical signal of high frequency that alters the normal voltage pattern (sine wave). An example of the result of noise would be the distorted picture you may get on a computer screen when a microwave is turned on. Possible causes include:
- Electronic equipment
- Radar transmitters
- Radio and television broadcasts
- Operation of welding equipment
- Heaters, thermostats and loose wiring
- Harmonic Distortion: Harmonic distortion is the alteration of the normal voltage pattern (sine wave) due to "non-linear" loads (like electronic equipment). All electronic devices (those having transistors for example) draw electricity differently than non-electronic equipment and distort the normal voltage pattern. Possible causes include:
- Operation of non-linear loads such as fluorescent ballasts and computer power supplies
- Operation of battery chargers
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Potential Power Reliability Solutions
To keep your business up and running with reliable power, some of the following equipment may be useful.
- Standby Generator
An alternate power supply usually driven by a gas or diesel engine.
- Surge Protector
Designed to limit instantaneous high voltages. Also known by a number of names, such as surge suppressor, surge arrestor and surge diverter.
- Noise Filter
Eliminates interference that may interrupt the proper operation of electrical or electronic equipment. This interference is known as electromagnetic interference (EMI). Electronic devices can be a source of this interference.
- Isolation Transformer
Protects sensitive electronic equipment by buffering electrical noise.
Voltage Regulator
Voltage regulators maintain voltage output within a desired limit despite varying input voltage. Regulators provide little or no protection against surges or noise.
Constant Voltage Transformer
Constant voltage transformers are designed to maintain a constant voltage output over a wide range of input voltages. As a result, input voltage variations do not pass through the transformer.
Uninterruptible Power Supply (UPS)
Uninterruptible power supplies are designed to improve the quality of power supplied to critical loads and to generate the required voltage and current when power interruptions, voltage variations, or frequency variations occur. A UPS has batteries as an internal source of energy and uses this energy to provide AC power to selected equipment even if the utility power is interrupted.
Motor-Generator Set
Motor-generator sets are designed to come between the power from the utility system and critical equipment within the business. The motor takes power from the utility system and then generates power for critical equipment. Acting as a buffer, motor-generator sets provide regulated, conditioned power to connected equipment.
Harmonic Filter
Harmonic filters are designed to limit the periodic or continuous distortions of the normal voltage wave pattern (sine wave) caused by non-linear loads. Non-linear loads (like all electronic equipment) draw electricity differently than linear loads and distort the normal voltage pattern.
Power Surges and Spikes
“Power surges” are an increase in the voltage that powers electrical equipment. Surges often go unnoticed, often lasting only 1/20th of a second, but they are much more common and destructive than you might think. According to recent studies, electrical equipment is constantly experiencing surges of varying power. Some of them can be absorbed by a power supply while a quality surge suppressor can only handle others. The most destructive power surges will wipe out anything that gets in their way.
Sources
In this power-hungry computer age, utility power systems are often pushed beyond their capacity, resulting in unstable, unreliable power for consumers. Overburdened power grids can generate powerful surges as they switch between sources or generate "rolling surges" when power is momentarily disrupted. Local sources can also generate surges (such as a motor starting, or a fuse blowing out).
Lightning
Lightning can generate a spectacular surge along any conductive line to destroy everything in its path. No matter what manufacturers may claim, no surge suppressor in the world can survive a direct lightning strike. However, with quality equipment, the surge suppressor will take the hit—ending up melted—but the equipment it protects will not be affected.
The Right Level of Protection
Joule ratings: The bigger, the better! Joule ratings measure a surge suppressor’s ability to absorb surges.
- 200 joules: Basic Protection
- 400 joules: Good Protection
- 600+ joules: Excellent Protection
Surge amp ratings: Higher ratings offer more protection. Amp levels are another important factor in determining surge strength. Look for the highest amp protection levels available.
UL 1449 Voltage Let-Through Ratings: Underwriter Laboratories tests each surge suppressor and rates them according to the amount of voltage they let through to connected equipment. The lower the let-through voltage, the better the surge suppressor is. UL established the 330 volt let-through as the benchmark because lower ratings added no real benefits to equipment protection, while surge components, forced to work harder, failed prematurely. Be wary of manufacturers claiming lower let-through ratings. |
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