Although you may be unfamiliar with the term “power quality” (PQ), you are likely aware of the consequences of PQ problems. Losing critical computer data to a blackout or experiencing damage to process or medical equipment due to a lightning strike are just two examples of how these problems can affect your business. Technically speaking, power quality refers to the degree to which electricity is free of disturbances that can cause electricity-consuming devices to malfunction or fail.
PQ problems can affect many types of equipment in your facility, but they’re especially hard on electronic equipment that’s dependent on microprocessors. Computers, network servers, energy management systems, industrial machinery, and food-processing or medical equipment could be damaged or fail prematurely if they are not protected from harmful voltage changes and related disturbances.
Electronic devices function properly as long as the voltage delivered to your facility falls within a consistent range. Power swells, sags, and momentary interruptions occur when the voltage fluctuates outside this normal range. Surge protection devices guard against power transients (low-energy events with a duration of less than 10 microseconds) and power surges (substantially higher energy events with a duration between 10 microseconds and 1 millisecond).
Utilities strive to provide highly reliable and consistent electric power, but it’s impossible to maintain perfectly constant voltage 100 percent of the time. In the course of normal utility operations, voltage will inevitably fluctuate as loads come on to or leave the power system.
PQ events also occur for reasons that have nothing to do with your utility. Lightning strikes can cause major power disturbances. More-subtle PQ problems often originate within the walls of your building and can be traced to the starting and stopping of refrigerator and air-conditioner motors, circuit overloads, or grounding and wiring problems. Onsite switching of power supplies—such as changing to backup power during an outage—is particularly problematic because it can cause PQ fluctuations.
Why is this important?
Problems caused by voltage fluctuation depend on the size of the disturbance, and they vary in severity from brief malfunctions to immediate equipment failure. Small fluctuations may not cause any problems initially, but, if left unchecked, these events can lead to equipment degradation over time. If a loss of data or productive time would have a significant impact on your business, or if the cost of replacing failed electronic equipment is high, you need to protect your company against PQ-related damage.
Since we last reported on these protection devices (in 2009), the nomenclature used by the industry has officially changed from transient voltage surge suppressors (TVSSs) to surge protection devices (SPDs). This change occurred with the third—and most recent—edition of Underwriters Laboratories (UL) standard 1449, the primary safety standard for these devices. Be aware that some manufacturers and vendors may still refer to them as TVSSs.
What are the options?
There are two major ways to protect your equipment from voltage transients. First, you can permanently install a device either before or after your electric meter—that is, at the point of entry. Second, you can install protection at the point of use, where sensitive pieces of equipment connect to electrical outlets. A combination of point-of-entry and point-of-use devices will provide the greatest level of protection.
The third edition of UL 1449 drills this down even further, and classifies SPDs into four types:
- Type 1 (point of entry). Permanently connected devices intended for installation before the service entrance disconnect (where the main power line enters the building, generally at the meter). These will have their own overcurrent protection—such as a fuse or circuit breaker—and were formerly called “secondary surge arrestors.”
- Type 2 (point of entry). Permanently connected devices intended for use after the service entrance disconnect. These can rely on the service entrance disconnect device for overcurrent protection.
- Type 3 (point of use). SPDs that are intended to be placed no more than 10 meters (approximately 33 feet) from the service panel, not including the length of the SPD conductors.
- Type 4 (component level). SPD components or assemblies, incomplete in and of themselves, that are intended for factory installation in other devices.
Panel-mount surge suppressors (UL 1449 type 2) can be installed in or adjacent to your electrical panels to provide protection throughout your facility. These panel-mount, or hard-wired, surge suppressors protect against transients that come through utility power lines (Figure 1). In addition, they can prevent transients that originate on one of your facility’s electrical circuits from affecting other circuits.
Transients caused by lightning can enter buildings through underground circuits that supply electricity for sprinkler systems, pole-mounted lights, outbuildings, or other external uses. A transient on one of these circuits could damage equipment on other circuits unless it’s blocked by a suppressor at the electrical panel. Transients from lightning can also enter your building through telephone and cable-television circuits. Special hard-wired suppressors can be installed on these circuits by a qualified electrician.
Another way to provide whole-facility protection is to use a meter-based SPD (UL 1449 type 1). Note, however, that these devices can only be installed by your utility; check to see if it offers an installation service for this kind of protection.
Point of use: Plug-in surge suppressors
Plug-in surge suppressors provide affordable, but somewhat limited, protection for sensitive equipment. Often designed as power strips with multiple outlets, they protect only the devices that are plugged into them (Figure 2). Other plug-in surge protectors fit over wall outlets. Some models include jacks for telephone lines, cable-television lines, or USB devices.
With USB devices becoming increasingly common in commercial and industrial (C&I) environments, you may want more protection for sensitive equipment. USB devices that are moved off of the desktop can be vulnerable to PQ issues due to longer cable runs and varying power sources with differences in ground voltage, not to mention such real-world effects as moisture and vibration. On a factory floor, for example, the ground potential of a wall outlet and a piece of industrial machinery may be different. If a computer is connected to both (plugged into the wall for power, and plugged into the machinery via USB), the USB cable will conduct the potential difference (called a ground loop), and its circuitry may be overloaded. Inline USB isolators will protect equipment from ground loops, spikes, and surges. Many come with high-retention USB ports that require greater force for insertion or removal of USB cables, and the cables themselves can be made hardier to protect against electrostatic discharge (ESD) or electromagnetic interference (EMI).
Can SPDs save energy?
A small number of SPD manufacturers and vendors continue to claim that their devices can save users substantial amounts of energy. However, we have yet to see a supposed mechanism for producing energy savings from an SPD that has not been thoroughly refuted. Our discussions with a sampling of SPD manufacturers indicate that the notion of energy savings from SPDs has been widely discredited in the industry. In fact, many states took action to bar manufacturers and vendors from making such claims. In 1993, the US Federal Trade Commission (FTC) showed its agreement when it forced one Florida vendor to stop marketing SPDs on the basis of energy savings.
Not only is there no credible mechanism by which SPDs could save an appreciable amount of energy, there is simply no opportunity for them to do so. An electric surge typically lasts less than one millisecond (one thousandth of a second). According to data prepared by the Institute of Electrical and Electronics Engineers (IEEE), we can conservatively estimate that a facility with “medium exposure” to voltage surge activity (one that is sited where there is medium to high lightning activity or that frequently suffers surges caused by load switching) would experience electric surges totaling less than 100 seconds per year. If an SPD could shut off all power to the building during a surge event, that would translate to only about 0.0003 percent energy savings.
Even in industrial facilities with the noisiest electrical environments, SPDs are active for no more than a very small fraction of time—about 0.01 percent of facility runtime. To provide energy savings of even 2 percent during such a brief period, these devices would have to cut power consumption by orders of magnitude greater than the average load—something they clearly do not do.
Companies that offer energy-saving “guarantees” for their SPDs invariably put the burden of proof on the customer and use month-to-month changes in whole-facility electric bills to demonstrate savings. But billing analyses are notoriously inaccurate because they fail to account for many variables that influence a facility’s overall electricity consumption. Accurately determining the impact of any single piece of mitigation equipment requires a sophisticated multivariate regression model that incorporates all of the variables that could influence consumption. If any data is missing or incomplete, the model will be unable to explain some portion of the monthly variation in electricity bills, and the consumer will be unable to prove the absence of SPD-derived savings.
SPDs do a great job of protecting electrical equipment, but purchasers would be wise to get multiple bids for any SPD installation and to steer clear of vendors that are promising energy savings.
How to make the best choice
Some devices are UL 1449 Listed, meaning that sample units have been found to meet the UL standard for surge suppressors. One of the metrics associated with UL Listing is the voltage protection rating (VPR), a number that indicates the maximum amount of voltage the suppressor will allow your equipment to be exposed to. The lower the VPR, the better the protection.
SPD equipment that complies with UL 1449 prior to the 2009 publication of the third edition is listed with a suppressed voltage rating (SVR) instead of a VPR. SVR is not comparable to VPR because, with the third edition of UL 1449, the testing procedure changed. Comparing them cannot tell you which device offers greater protection—it’s apples to oranges—and UL changed the nomenclature to avoid confusion.
You can purchase plug-in surge suppressors from computer, hardware, and office-supply stores for anywhere from $10 to more than $100. Keep in mind that a higher price doesn’t ensure a higher level of protection. Table 1 presents selection criteria for these devices. The more-effective units combine several different transient-protection components. Sine wave tracking is a sophisticated feature that is advisable only if you have equipment that is particularly sensitive to harmonic distortion; this is not an issue for most small businesses.
Some manufacturers offer remote (in some cases Internet-based) monitoring and notification when an SPD device is no longer providing protection to a circuit. This option might be useful in an industrial facility with widely dispersed critical process controllers or for companies with numerous geographically dispersed facilities.
Who are the manufacturers?
This is a partial list of surge protection device manufacturers.
- ABB Power Protection
- Advancetech B&B SmartWorx
- American Power Conversion (a Schneider Electric brand)
- ASCO Power Technologies (a Schneider Electric brand)
- Bussmann (Eaton)
- General Electric
- Meter-Treater Inc.
- SurgeArrest (Schneider Electric)
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