Transient Voltage Surge Suppressors

Transient Voltage Surge Suppressors

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 caused by 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, especially electronic equipment dependent on microprocessors. Computers, network servers, energy management systems, machinery, and food-processing and medical equipment might 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. Surges, transients, sags, and momentary interruptions occur when the voltage fluctuates outside this normal range.

Utilities strive to provide highly reliable and consistent electric power. In the course of normal utility operations, however, voltage will inevitably fluctuate as loads come onto or leave the power system or the utility switches among various sources of electricity supply. It is impossible for utilities to maintain perfectly constant voltage 100 percent of the time.

PQ events also occur for reasons that have nothing to do with your utility. Lightning strikes can cause major power surges. 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.

Why Is This Important?
Depending on the size of the voltage fluctuation, PQ problems can vary in severity, ranging 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.

What Are the Options?

There are two major ways to protect your equipment from surges. First, you can provide protection at the point of entry: that is, at your electrical panel or meter. 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.

Point-of-Entry Protection: Meter-Based Devices

Some utilities lease surge-suppression devices that are attached to the electric meter (Figure 1). These devices go by various names, including whole-house surge suppressors, secondary surge arrestors, and meter-socket adaptors. They provide the first line of defense against surges that come through utility power lines. A meter-based suppressor can only be installed by your utility.

[Note: some utilities explicitly prohibit meter-based surge suppression. In that case, use the panel-based or point-of-use solutions discussed below.]

Figure 1: Meter-based surge arrestors

This device, mounted underneath the meter, traps surges at the point of entry.
Courtesy: Meter-Treater Inc.

Point-of-Entry Protection: Panel-Mount Suppressors

Another type of surge suppressor can be installed in or adjacent to your facility's electrical panel(s). These panel-mount or hard-wired surge suppressors protect against surges that come through utility power lines (Figure 2). Additionally, they can prevent surges that originate on one of your facility's electrical circuits from spreading to other circuits.

Figure 2: Panel-mount suppressors
This is an example of a panel-mount device for surge suppression that is located in a small manufacturing facility.
Courtesy: Danaher Power Solutions

Surges caused by lightning can enter buildings through underground circuits that supply electricity for sprinkler systems, pole-mounted lights, outbuildings, or other external uses. A surge received on one of these circuits could damage equipment on other circuits unless blocked by a suppressor at the electrical panel. Surges 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.

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 3). Other plug-in surge protectors fit over wall outlets. Some models include jacks for telephone and cable-television lines.

Figure 3: Plug-in surge suppressors
This plug-in device incorporates status lights as well as input and output jacks to protect a phone line.
Courtesy: Tripp Lite

Top of Page

You should select devices that are UL 1449 Listed, meaning that samples have been found to meet the Underwriters Laboratories (UL) standard for surge suppressors. Associated with the UL listing is a number indicating the maximum amount of voltage the suppressor will allow your equipment to be exposed to. The lower this voltage rating, the better.

You can purchase plug-in surge suppressors from computer, hardware, and office supply stores for anywhere from $10 to more than $100. A higher price doesn't ensure a higher level of protection. See Table 1 for selection criteria. The more effective units combine several different surge-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.
Table 1: Choosing plug-in surge suppressors

Surge-suppression rating
Protection method
Additional features

UL Listed at 500 watts
1,000 surges at 2,000 volts and 1,000 amps
Surges are diverted to ground.

UL Listed at 400 watts
1,000 surges at 4,000 volts and 2,000 amps
Surges are absorbed and not diverted to ground circuit.
Indicator lights (showing that surge suppression is working, not just that the device is plugged in).

UL Listed at 330 watts or below
1,000 surges at 6,000 volts and 3,000 amps
Surges are absorbed by multiple, redundant internal components.
Data port protection, sine wave tracking, phone/fax/coaxial plug-ins, metal housing, space to accomodate transformer plugs, and warranties offered to cover damage to equipment connected to the suppressor.

A change in the national electrical code in January 2002 required that transient voltage surge suppressor (TVSS) devices be rated to carry the fault current capability (that is, the amount of current that a phase conductor would carry in the case of a bolted fault to ground) of the circuit to which they are connected. This change created a flurry of activity among TVSS manufacturers, as many designs were not previously required to carry these currents and could catch on fire under certain conditions. Now UL1449 requires all surge suppressors to identify the approved short-circuit current rating for the product.

Another new development is that manufacturers have begun to offer remote (in some cases Internet-based) monitoring and notification when a TVSS device is no longer providing protection to a circuit. This option might be useful in an industrial facility with numerous, widely dispersed critical process controllers or for companies with numerous geographically dispersed facilities.