FMS Articles

Plan to Avoid Havoc from Electromagnetic Interference

Many experts will agree that it is essential for facility managers to stay abreast of new developments in office technology. Current trends towards increased dependence on sophisticated technology in the workplace means a number of inherent changes in how we manage our commercial, industrial and institutional facilities. While much of the focus to date has been on the equipment, furniture or cabling necessary to support future technological demands, there is another dimension of planning that is also essential - planning for potential electromagnetic interference (EMI).

A number of facilities are preparing to incorporate wireless voice and data systems over the next few years and are investigating potential conflicts from high frequency sources. EMI though can occur at much lower frequencies, and from much more common sources including the building's own power infrastructure.

Even with increased efficiency, electricity is expected to account for about 75 percent of energy consumed by the commercial sector in the year 2020. According to a recent forecast released by the U.S Department of Energy, "Energy use for personal computers is projected to grow by 4.5 percent per year and for other office equipment, such as fax machines and copiers, by about 3.5 percent per year." And, as the use of electricity increases, so will the potential for EMI from power frequency (50/60 Hz) sources.

The Physics of the Problem

Anytime you use electricity, you generate electric and magnetic fields (EMF). But as electric fields are easily blocked by common building materials, most of the concern is focused on the magnetic fields. Because magnetic fields vary proportionately based on the amount of current being used, facilities that use more electricity will have higher fields. This is especially true for technology companies, which are expected to use as much as 30% of the nation's electricity in coming years.

In most facilities, the areas adjacent to high current carrying devices such as external transmission lines, transformers, service panels and conduit will have elevated levels of EMF. In commercial buildings, the average level of magnetic fields will typically fall in a range of 0.5 and 4 milliGauss (mG), but in areas of high current concentration, values greatly above these are common.

Interference with equipment such as CRT monitors, CPUs, data networks and medical devices can occur anytime the external magnetic fields are stronger than a unit's internal fields. The threshold level for interference will vary depending on the type of equipment being used. Generally, the more sophisticated and technologically advanced the equipment is, the more susceptible it is to interference. For example, graphics workstations tend to have highly sensitive CRT monitors that can exhibit instability, or "jitter," in fields as low as 3-5 mG, but almost all CRT monitors will become unstable above 10 mG.

Identifying and Managing EMI Problems

There are several strategies to manage an EMI problem, but the first step is identifying the correct source of the problem. Generally the local utility or electricity supplier can provide a low or no-cost preliminary survey. If they find elevated fields, or if the space in question is not under full load, then an independent assessment can be helpful. Some firms in this field can also offer computer modeling to forecast the field levels under future, increased loads. They will also be able to provide a mitigation plan in case the facilities' management opts to restore the space to full utility.

The mitigation steps taken must be appropriate to the characteristics of the source in order to be effective. The symptoms of the interference will help point the way to the cure. If the interference varies with the building's power load, with spikes when air conditioning is used for example, then the source is very likely a current-carrying device. If the fields are moderately elevated, but spread out over a wide area, then it is likely there is a "net-current" problem caused by wiring errors.

There are three basic strategies to deal with a magnetic field problem. The first is to increase the distance between the source and the affected device. Because fields from power sources fall off quickly with distance, it may be possible to create an environment in which technology can function properly simply by using space as a buffer between the device and the source. When space is not at a premium value, this option can be the least expensive.

The second strategy is to lower the levels of the fields. Obviously it usually not possible to lower the load on the power infrastructure, but it is frequently possible to employ specialized engineering techniques to create the natural conditions under which the fields will naturally cancel themselves. Depending on the source, field reduction can be achieved by correcting wiring errors, re-phasing distribution lines or compacting cabling.

Finally, depending on the source, shielding of the affected device, area or source may be desirable to enable technology operations. CRT monitor shields or other device shielding can provide a quick, if temporary, solution to interference problems. When elevated fields affect a wide area, some facility managers will opt for room or area shielding. While this solution may require a larger investment than other options, it frequently provides a permanent solution and a greater ROI as the space may then be used at full utility.

Avoiding Future EMI Problems

The best strategy to avoid costly, and sometimes embarrassing, shielding and mitigation projects is good space planning. When laying out new space or rearranging current space, identify all the major sources of AC and DC current, including transformers, electric panels, major conduit paths, elevators, etc. Office space closest to these areas can be designated as "low-technology" areas. Space with elevated magnetic fields can be turned into hallways, storerooms, or lounge areas. Individual devices as well will emit fields and can interfere with other equipment so care should be taken when arranging these items to ensure compatibility.

It is also advisable to get a survey performed with the space under load. If there are any planned changes in the building's power infrastructure, it may be extremely valuable to engage a firm to do modeling of the fields. With this data, designers can visualize where the problem areas will most likely be and effectively plan to avoid or mitigate potential interference. Above all, make certain that all electrical work is done in strict conformance to code, particularly those elements of code which pertain to grounding.

When doing long term forecasting, be aware that future increases in technology usage will impact the building's energy load. If it is possible to estimate future energy demands, then it will be possible to use these other tools available to forecast the impact on the building's magnetic fields.

Case Study

Recently, a developer in St. Louis, Missouri was alerted to a potential EMI problem in his newly completed five-story commercial office-building project. The building is located adjacent (within 75 feet) of a double circuit 345 kV high voltage transmission line, so the developer opted to have a magnetic field survey conducted to assess the potential impact on the office space. Field Management Services conducted the survey and noted elevated magnetic field conditions (greater than 5 mG) in a 7,000 to 8,000 square feet area on each of the building's five floors, in the corner area closest to the passing transmission lines.

Based on a review of the building site, characteristics of the passing power lines and magnetic field measurements taken throughout the building, Field Management Services provided a multifaceted mitigation plan. Utilizing computer simulation studies, Field Management Services recommended that certain electrical changes be made to the phasing of the 345 kV transmission line. Computer simulations indicated that EMF reductions in the order of 40% to 50% could be potentially achieved by rephrasing of the transmission lines. The local utility was approached by the building developer and subsequently agreed to implement the rephrasing recommendations. Magnetic field measurements taken in the building after the changes to the 345 kV transmission line were completed, confirmed that EMF levels in the building were reduced by approximately 40%.

However, small areas (less than 2,000 sq ft) of the building remained with slightly elevated levels of EMF present after rephrasing of the transmission lines. These areas on each floor were corner areas immediately adjacent to the exterior 345 kV transmission lines.

Again, utilizing the after-rephasing magnetic field measurement data and computer simulation studies, Field Management Services developed a special magnetic field shielding scheme to further reduce levels of EMF in these areas. Special magnetic field shielding material was subsequently installed on a portion of each floor slab on each building level and on a small section of wall areas beneath the exterior windows. Measurements taken after installation of the shielding material on all five floors, confirmed that EMF levels had been successfully lowered to levels that would enable the use of current office technology.

About the author

Michael L. Hiles is president of the Los Angeles-based Field Management Services. With a background in electrical engineering, he has served in a number of capacities in the television, telecommunications, videographic, and teleconferencing systems industries. He regularly speaks about topics involving magnetic fields. He can be reached at Michael.Hiles@FMS-Corp.com.