Will My Surge Suppressor Work?: With the U.S. government surge suppressir classification system, we finally have a rational basis for selection.

Sep 1, 1997 12:00 PM, J. Rudy Harford

When you buy a new audio component or system, you immediately check to see if you are pleased with the performance. How will you check a new powerline surge suppressor?

This article discusses surge suppressor classification and performance verification developed by the U.S. government for its own needs. We will also discuss how you can take advantage of the government's work and how MOV technology and series-mode technology compare against the performance criteria established.

Effective protection Although the need for power-line surge protection and noise filtering may be obvious, a serious surge could prove your protection inadequate. How can you be sure of your protection?

Fortunately for all of us, the U.S. government had the same problem. Fortunately because they actually provided the means to fix the problem. They developed Performance Verification Testing to supplement the UL safety testing. This performance testing classifies products according to demonstrated performance based on tests done at an independent testing laboratory. Underwriters Laboratories (UL) was chosen for this performance testing because the company has the necessary specialized equipment (its surge generators cost about $70,000) and trained specialists to operate this equipment, which UL also uses to perform safety testing.

The government classification system is based on the needs of the user and does not rely on any particular suppressor technology to describe the product tests, making it universally applicable. The system is so basic it can be used by everyone. Just understand the following fundamental issues and you can't go wrong.

Endurance (reliability): Defined in three grades - A, B and C.

Performance: Defined as class 1, 2, or 3 within each grade.

Application: Modes 1 and 2 are defined, recognizing differences in suppressor design that affects proper application of the suppressors. This is especially important for audio and video applications.

Safety: A suppressor design must be tested and certified to UL 1449. UL 1449 is the safety standard for power-line surge suppressors. Because the government standard also calls for filtering performance, the design must also meet the UL 1283 (filter) safety standards.

Certification: Responding to government and industry needs, UL has developed a performance testing service called the Adjunct Classification Testing Service. At the request of the manufacturer, UL will attach the performance test results to the manufacturers' standard UL 1449 safety testing records. This new testing service will test and certify performance to the new government performance verification standards. The UL1449 safety testing done by UL does not assure any level of performance or endurance for any particular application - only safety. This new aAdjunct testing is not performed by UL unless specifically requested by the surge suppressor manufacturer. Of course, manufacturers of quality products will have requested this service and will readily supply you with the test information.

To establish a product endurance grade, a surge suppressor is tested with 1,000 surges, using industry standard waveforms.

Grade A: 6,000 V, 3,000 A.

Grade B: 4,000 V, 2,000 A.

Grade C: 2,000 V, 1,000 A.

The performance class is also determined during the endurance testing. A class 1 product "suppressed voltage" (sometimes called let-through voltage or effective clamping voltage) must be less than 330 V. A recent study has shown that class 1 performance (less than 330 V suppressed voltage at the design surge current) is required to protect equipment that uses a switch-mode power supply. A Class 2 product suppressed voltage is greater than 330 V but less than 400 V. A Class 3 product suppressed voltage is greater than 400 V but less than 500 V.

Two modes are defined. The proper mode to use depends on your application and is important. Using the wrong mode may do more harm than good! Mode 1 protects line to neutral, avoiding ground wire contamination (often described as L-N, or line to neutral suppression). Note that the terms ground wire, safety ground wire and ground wire circuit make reference to the green equipment grounding wire. Mode 2 products divert surges to the safety ground wire, thus contaminating this voltage reference wire with surges (often described as all three modes, L-G, L-N, N-G).

Although this government classification system was introduced in 1996, manufacturers of safe, effective products moved swiftly to embrace it. Many suppressors have been qualified to the highest Classification of class 1, grade A, mode 1, in 1996 and 1997.

The graph shown in Figure 1 compares the government performance verification testing with UL 1449 (surge suppressor safety) and new CSA (Canadian) requirements, showing that the limited number of low-level surges applied during safety testing are too few and at too low a level to give a useful indication of product endurance.

The Grade A, B and C classification system is based on the American National Standard ANSI C62.41-1991 (formerly IEEE 587) as shown in Table A. Performance class, shown in Table B, is based on UL 1449 SVR (suppressed voltage ratings) categories.

Which mode do you need? Mode is extremely important. You should select the mode carefully to meet your application. Mode 1, the most versatile mode, can be used for an interconnected or stand-alone environment. If two or more pieces of equipment are interconnected with a cable other than the power wire (video cable, printer cable, audio cable, network cable, phone line) and the equipment is not all connected to the same power outlet receptacle, mode 1 should be used.

Mode 2 should be used for stand-alone applications, where all equipment shares a common power outlet receptacle or no interconnecting wires are used. An example would be a microwave oven. Mode 2 products use the ground wire for surge diversion, which can cause a variety of problems.

Ground wire contamination Although the neutral wire and green ground wire both return to earth ground at the service entrance, the ground wire carries no equipment load current and is assumed to be free from electrical activity and noise. Therefore, this wire is used as a zero voltage ground reference in the audio-video electrical environment. When a mode 2 product is used in this environment, you will could see the introduction of hum and buzz into audio systems, horizontal bars in the video and random noise in audio and video signals. These noise distortions occur when an MOV clamp level is too low or when continuous noise sources, such as SCRs or some lighting and motor control circuits, are in use. Mode 2 suppressors inherently divert electrical noise to this most sensitive ground wire.

Surges diverted to the ground wire may be disruptive to computer systems, demanding supplemental protection on the datalines, but it is disastrous to audio-video systems, which are much more susceptible to low levels of noise.

Providing protection from damaging voltages diverted to the ground wire by a mode 2 product is the least of the problems. Eliminating the noise is a far more difficult issue. If system noise is a concern, mode 2 products should only be used at the service entrance of a building, where the neutral and ground wires are bonded together.

A mode 2 product is often described as "all three modes of protection," meaning surges are diverted to the ground wire as well as the neutral wire. Use this type of product very selectively.

The best protection The best surge suppressor for important audio-video applications would carry the class 1, grade A, mode 1 classification, which would be certified to 1,000 surges of 6,000 V, 3,000 A with a suppressed voltage rating of 330 V measured with the 3,000 A surge and would not contaminate the safety ground wire with surges.

Many manufacturers claim their products will suppress 6,000 V surges at greater than the 3,000 A called for by this new testing. Many of these claims are unverified and are simply the summation of the individual component ratings - something like saying you can go 200,000 miles on your tires because each tire (including the spare tire) is rated for 40,000 miles. Unless you can test them yourself, an independent laboratory such as UL should verify these claims using standardized tests and should classify the products according to the test results, which is exactly what the government has made available to us. All we have to do is ask for the test results. If a manufacturer does not have the test results, there might be a good reason!

If you take advantage of this new government classification system, you will have the means to make an informed decision because price and performance can be qualified in a meaningful, standardized way.

This classification system was officially issued in July 1996, and manufacturers of high-performance products have had time to have their products classified under the program. Ask your supplier for the information. If your application is important, insist on seeing the documentation. For such applications, insist on a verified class 1, grade A, mode 1 product. These products are now available from multiple suppliers. The alternative is simply to gamble on your protection and risk exposure to suppressor-induced electrical noise and damage.

Suppressor replacement schedule Most surge suppressors in use today use components (MOVs) that wear out with use, and a replacement schedule for these products should be planned before failure occurs. Quoting from one manufacturer that acknowledges this problem with their MOV products, "All (our) surge suppressors are eroded by every surge they absorb ... All have limited capacity. Once that capacity is reached, the unit is no longer protecting your equipment and should be replaced."

Unfortunately, few suppressors have established meaningful endurance ratings, making it almost impossible to predict when to replace them. If your application is important to you, your company or your customers, it is probably prudent to replace any suppressor that is more than a year old unless it has a demonstrated endurance capability of grade A, B or C. A certified grade A, class 1 product should provide continuing protection in the most severe electrical environment for about 10 years. The MOV endurance ratings in the following section may give you some guidance concerning a replacement schedule.

Technology issues Although the new classification system does not reference any particular technology, technology plays a key role in being able to provide the desired performance and endurance.

The dominant technology in use today is MOV shunt, or surge diversion technology, principally because MOVs are inexpensive and have large one-time surge ratings.

As a consequence of the large one-time surge rating, manufacturers emphasize this rating but may neglect to inform you that it is a one-time rating. In other words, the device can be expected to fail if exposed to a second such surge.

MOVs with endurance ratings of 14 mm and 20 mm are commonly used. Table C shows their endurance ratings (sometimes called pulse ratings or pulse life ratings) as taken from MOV manufacturers' data sheets for the industry-standard 8/20 microsecond current wave.

Because MOVs have limited endurance, manufacturers of surge suppressors using MOVs often provide a failure indicator on their products. A failure indicator tells us the product is prone to failure, but worse yet, it is virtually useless for several reasons, the most significant of which is that the MOV failure will most likely be discovered when equipment fails at the same time. Isn't it better to use components that are not designed to fail in the application? The cost of down-time, re-work caused by noise and equipment damage is most certainly greater than the incremental cost of high-performance, verified protection.

The clamping level of an MOV often given is the onset of clamping, not the effective clamping level (suppressed voltage). For instance, for the Harris Semiconductor (formerly GE) V130LA20A, with industry standard 8/20 surges, the maximum rms voltage is 130 V, the varistor clamping voltage at 1 mA is 200 V, the maximum clamping voltage at 100 A is 340 V and the maximum clamping voltage at 3,000 A is 500 V.

A surge suppressor rated by a suppressor manufacturer for a clamping level of 200 V may actually have an effective clamping level (suppressed voltage) of 500 V, a specification not often acknowledged by the suppressor manufacturer.

When a surge hits, the MOV clamping level tends to drift from the initial value. If the clamping level drifts low, the MOV can start conducting on the peak of the power wave, introducing system noise, and go into thermal run-away, catch fire or explode. If the clamp level drifts higher, the effectiveness is degraded.

To reduce the chance of fire and explosion, some manufacturers are using the higher voltage MOV, such as the Harris V150LA20A, which has a maximum rms voltage of 150 V, a varistor clamping voltage at 1 mA of 240 V, a maximum clamping voltage at 100 A of 395 V and a maximum clamping voltage at 3,000 A of 580 V. As you can see, the effective clamping level (suppressed voltage) at surge currents of 3,000 A (the highest surge current called for in the U.S. government classification system) is almost 600 V, not the 240 volts likely to be claimed.

Some manufacturers use multiple MOVs and simply sum the individual MOV ratings and rate their product accordingly. Before you buy into such a scheme, insist on seeing test data from an independent lab, data that includes clamping level (suppressed voltage) at the desired surge current as well as endurance test results.

>From the MOV endurance ratings just presented, it is clear that meeting the highest levels of the new U.S. government classification system standards by suppressing 1,000 large surges using 14 mm or 20 mm MOVs would be challenging.

An alternative technology In the effort to provide improved endurance, reduced ground wire surge contamination and improved effective clamping level (suppressed voltage) performance, a technology using filter concepts has emerged. The technology is based on the concept shown in Figure 2.

If the surge can be sensed and a switch opened during the very brief moment of the surge, and if the switch closes immediately after the surge, the surge would simply disappear with no harm done to the protected equipment and no ground wire circuit contamination. The industry-standard 8/20 surge lasts for less than 1% (20 [micro]s) of the powerline cycle (16.67 ms). Such a short interruption of power would have no discernible effect on the protected equipment.

This concept is embodied in the design of the series mode suppressor shown in simplified form in Figure 3. Because no sacrificial components (such as MOVs) are used and filters do not wear out from use, no inherent endurance limitation exists for this technology. Indeed, this is the first technology to pass the new U.S. government classification system to the highest levels of performance and endurance.

Basically, the series inductor (called a surge reactor by some manufacturers) is designed to be "transparent" to the power wave but acts like an open circuit to surge frequencies, keeping them from entering the protected equipment. This is the same principle used by all inductor input L-C filters, which let the desired frequencies pass unabated but stop the undesired frequencies.

The secret here is to use materials for the series inductor, which work effectively even with high voltages and high currents applied. A major problem with the inductor design is that, to reduce the cost of the inductor, a manufacturer might use certain core materials that make the inductor small and inexpensive but will go into magnetic saturation under surge conditions of high surge voltage and high surge current, rendering the inductor ineffective for suppressing surges. Handling 6,000 V and 3,000 A (up to 4.5 million W) requires appropriately sized components.

Do your homework No matter what the actual technology for the product, if you rely on the U.S. government classification system, you have a powerful new tool that can give you a high level of confidence in the products you purchase or specify. But you must use this tool effectively, as with any other tool you have at your disposal.

In 1996, series mode technology has passed to the grade A, class 1, mode 1 performance level of the new U.S. government performance classification system, withstanding 1,000 surges of 3,000 A with a suppressed voltage of less then 300 V.

As with most products, superior performance and endurance justifies a higher price. Now you have a rational basis for your selection and can invest your money or your customers' money wisely. Before this classification system and certification by UL, you could pay a lot for a surge suppressor without receiving any assurance of the superior performance and endurance your equipment may need.

Clamping level (clamping onset level): This generally is used by manufacturers to describe the voltage level that causes the surge diversion device to start diverting surge energy (usually at 1 mA of current, well below the maximum rated current). Related but more important parameters are the suppressed voltage (the term used by UL), effective clamping level (when discussing shunt-mode suppressors) and let-through voltage (when discussing series-mode or shunt mode suppressors).

Effective clamping level: This is the residual surge voltage left after voltage clamping when measured at the suppressor output for the specified surge current (1,000 A , 2,000 A, 3,000 A , etc.).

Filter: An electronic device that allows only certain frequencies to pass from the input to the output.

Ground: For safety reasons, electrical systems in the USA have a wire connected to earth ground at the service entrance. This ground wire is run along with the two current-carrying wires. Most electrical equipment chassis are electrically connected to this wire when a three-wire plug is used to connect the equipment to the electrical power receptacle. This third, non-current-carrying conductor, which is connected to earth ground at the service entrance of a building, is often referred to as ground, equipment ground or electrical ground wire.

Ground contamination: The designers of electrical equipment assume that equipment connected to the electrical ground wire is at ground potential, that is, all at the same voltage. When equipment is electrically interconnected with audio, video or data cables, and surges or other noise is diverted into the ground wire, ground wire contamination occurs, which can show up as hum, buzz or noise in audio systems, or noise or horizontal bars in video systems.

Inductor: An electrical component that opposes the flow of electric current. An inductor has the property of impedance, the opposition to the flow of electric current. Impedance changes value with the frequency of the applied electricity. When properly designed, an inductor can permit power frequencies to pass unabated while opposing surge frequencies, which are much higher frequencies than the power frequency.

Let-through voltage: The peak voltage that is let through a surge protection device from a surge to the protected equipment. The theoretical lower limit is about 180 V peak for standard 120 VAC power. Lower is better. Also called SV (suppressed voltage) by UL. An important measure of suppressor performance.

MOV: metal oxide varistor. This is an electrical component that is essentially an open circuit for lower voltages but becomes highly conductive after a certain voltage is exceeded for a certain length of time. The common 14 mm and 20 mm MOVs are about the size of a quarter and have high one-time surge current ratings. These components wear out with use and should be replaced periodically.

Noise: An undesirable signal that rides on the desired power signal and, although generally irregular and of relatively low amplitude, occurs frequently enough or is large enough to be of concern.

Series mode: A form of surge suppressor that uses an inductor as the first element to oppose the surge. The inductor opposes surge current and voltage, as compared to shunt mode, which diverts surge current and clamps surge voltage. Series mode is characterized by this large input inductor in series with the power line. An MOV followed by an inductor is shunt mode, not series mode, because the surge is first diverted and only residual surge energy is subjected to the inductor.

Shunt mode: A simple form of surge suppressor that diverts surge current and clamps surge voltage.

Suppressed voltage: The residual surge voltage at the output of a surge suppressor at the specified surge current; also called let-through voltage. In the case of simple shunt suppressors, this is essentially the same as the effective clamping level.

Suppressed voltage rating: UL has established a series of voltages for identifying the voltage suppression performance of suppressors, the first four of which are 330V, 400V, 500V and 600V, when tested to the specified surge current. The UL 1449 safety standard may call for 500 A test current while the adjunct classification testing may call for 1,000 A, 2,000 A or 3,000 A as a test current for establishing the suppressed voltage rating. A suppressor that has a suppressed voltage rating of 330 V at 500 A under the UL 1449 safety testing may have a suppressed voltage rating of 500 V when tested at 3,000 A under the adjunct classification testing because 3,000 A is a much more severe test than 500 A. For comparing suppressed voltage ratings, therefore, you must know the testing surge current levels.

Surge: A brief transient wave of voltage, current or power in an electrical circuit, lasting for less than 1% of the power wave cycle duration, generally occurring infrequently, caused principally by lightning and equipment switching operations.

UL1449, UL1283: UL1449 is the UL safety testing standard for power-line surge suppressors. UL1283 is the UL safety testing standard for power-line filters. A surge suppressor that is also a filter may have to be tested to both safety standards. Passing to UL1449 or UL1283 does not assure that a suppressor will actually suppress surges effectively, only that the suppressor has been found to be safe after suppressing a limited number of surges. UL1449 does not establish an endurance rating for surge suppressors. A suppressor may fail to function after several surges and still be judged safe and pass UL1449.