POWER QUALITY FOR SOUND & VIDEO

Will My Surge Suppressor Work?

With the U.S. government's surge suppressor classification system, we finally have a rational basis for selection

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 powerline 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 Adjunct 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 3 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.

Figure 1. UL 1449, CSA and new government surge exposure standards.

Which mode do you need?

Mode is extremely important. You should select the mode carefully to meet your application. Mode I, the most versatile mode, can be used for an interconnected or stand-alone environment. If two or more pieces of equipment arc 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.