FMS Publications

Power Quality, ELF Magnetic Fields and Real Estate Leases

ABSTRACT:

A new tenant, with sensitive display equipment, requires both clean power and an environment free of magnetic field interference. A valuable real estate lease deal, in mid-town Manhattan, turns on the power quality of the building and the ability to reduce environmental fields from the building electrical distribution system. Solutions to the existing problems will require coordination between the building electrical department, power quality consultants and the local utility.

1. THE PROBLEM:

Preliminary measurements by the local utility, confirmed by a New York power quality consultant, indicate that substantial parts of a 30,000 sq. ft. space will be unsuitable for the business requirements of the prospective tenant. Power quality issues, power frequency magnetic fields and DC fields from a subway line are concerns that must be resolved before a lease can be signed.

2. OBJECTIVE:

An agreement was needed, that took account of the various business and technical interests, with the rental space acceptable to the prospect tenant. All parties to the agreement would need to accept some level of risk in the cost and the potential for remediation, and terms were needed in the agreement that would limit the exposure to those risks for all parties.

Although the lease agreement would be a legal document, it would be shaped by highly specialized technical work with the building's power system - power quality, building wiring practices and EMF mitigation would each play a role.

The building management and electrical contractor, working with the local electrical utility, contracted with New York power quality experts American Power Technologies (APT) and Los Angeles magnetic field specialist, Field Management Services (FMS) to analyze the extent of the problems and to make recommendations for corrective action. At the same time, the tenant, the building owner and FMS worked toward an agreement for interference specifications that could form the basis for an acceptable lease specification.

Unfortunately, there are no performance or safety specifications for the problems in any of the three areas of concern:

1. Power frequency magnetic or electric fields,
2. DC magnetic fields
3. Slowly varying (sub-10 Hz) magnetic fields

Each of these problem areas would require development of a unique threshold interference specification and would, ultimately, require a unique set of solutions developed from its own research effort.

This paper is limited to the development of acceptable interference threshold specifications for power frequency magnetic fields from multiple sources, generated by quite different causes, and describes the measures taken in each case, to ameliorate these fields.

3. METHOD:

The test method combined the analytical issues of a laboratory experiment with the realities of a real-world problem.

Three questions were at issue:

• What were the characteristics of a threshold interference specification for power frequency fields, given a range of computer displays?
• What were the conditions with respect to these characteristics in the proposed tenant space and what were their sources?
• To the extent that the existing conditions violated the interference specifications, what field mitigation measures were available to economically restore the space to acceptable levels?

A. What were the interference thresholds?

First on the agenda was the establishment of acceptable ambient field levels at 60 Hz and its immediate harmonics. The tenant had different requirements for each of three, and possibly more, computer/monitor combinations. There is considerable literature on the interference threshold of computer monitors, but that work concludes that each monitor/computer is unique. Therefore, the most prudent course would be to test each of the tenant's combinations, at actual site locations, and to correlate the results with magnetic fields strength readings.

The most demanding were large format (21"), high definition Macintosh systems used for training. These became unstable in anything greater than a 6 milliGauss (mG) field. The administration systems would be standard Windows 17" displays. These systems exhibited sensitivity at or above 10 mG. Finally, the 17" LCD (flat screen) displays, also used by administration personnel, were essentially immune to interference throughout the space.

B. What levels were in the space and what were their sources?

A thorough magnetic field survey revealed 4 areas of elevated fields: two that were along perpendicular walls (most likely caused by high voltage cables in the street), one that was adjacent to a partially-abandoned utility transformer vault and finally, one area that was adjacent to the main building network protection vault. With the exception of the area in front of the main vault, the fields were the result of high current loads and separated conductors - called "spatial" fields. Measurements in these areas display a typical rate of decline of 1/d². In contrast to this, values in certain areas adjacent to the main vault declined at the signature a rate of a "net current" source: 1/d. The slower rate of decay produced higher levels of fields across a much larger area than would be expected from the more common "spatial" fields.

C. What field mitigation measures are available for these sources?

Since the fields fall off with distance, the first level of field mitigation to be considered involves space planning. In this strategy, the space planner designs the use of space to accommodate elevated fields. Where possible, troublesome space is assigned to uses that will not involve the use of sensitive technology. Libraries, meeting rooms, conference facilities, hallways and bathrooms are all productive uses for areas with elevated fields.

To the extent that this strategy would not compromise the tenant's space plan for the area, each of the areas that had elevated fields could be downgraded for uses that would not involve sensitive technology. Careful space planning, in many cases, will obviate the need for more costly measures.

For areas not amenable to space planning, and in those areas without "net current" fields, it was possible to design a custom shield and thereby reduce the fields to acceptable levels. Accordingly, custom shields were designed for critical parts of three of the four areas. In the areas with high current and net current fields, a combination of engineering measures and shielding is required.

4. RESULTS:

In the three areas without net current fields, the results of the shielding were so successful that there were no restrictions on the use of the space. The field levels had been reduced such that interference from power frequency fields were no longer at issue.

In the area adjacent to the network vault, the fields were substantially reduced by the shielding, and to within the desired interference specification. However, it is unlikely that these levels would have been achieved without the diligent effort by the building management, working with the power quality consultant, APT, to reduce the net current fields by engineering and wiring measures. This is complicated and tedious work, beginning at the top of the building and working down, but, inasmuch as the work to reduce the net currents required APT to "clean the building from top to bottom," the net current corrections had the ancillary benefit of eliminating the majority of elevated fields throughout the upper floors of the building.

5. CONCLUSION:

The requirements of this tenant brought together organizations with quite different skills, contributions and agendas. In the end, the agreements that concluded with a lease for a large part of a Class A building were the result of this disparate group working productively together. The lease memorialized the technical and economic limits of all of the parties and was based on realistic, real world specifications.