Setting Field-Level Objectives

In the March 2001 issue, the authors of “Power Quality Compatibility and Compliance” talk about an average field strength of 29.1 milliGauss (mG). They worked to get down to 5 mG to 6 mG, as if there is a requirement for that level.

Supposedly, people with pacemakers should not be exposed to more than 0.5 milliTesla. If I did the math right, this is equivalent to 5 gauss. Is there a requirement or rule-of-thumb that covers the 5 mG to 6 mG at 60 Hz?
Jack Wright
Berkshire Associates

Author's response: Setting field-level objectives in a mitigation project is always specific and comes from the negotiation process among the various interests at the table.

In this case, the 5 mG to 6 mG AC field level was set for the sensitivity of the tenant's computer monitors, which were unstable above these levels. Pacemakers also have high-level sensitivities, but there are many other equipment types that are even more sensitive, including analytical and medical diagnostic equipment.

For this reason, some companies set data interference levels at 10 mG to 50 mG. If the levels are set incorrectly, the results can range from unfortunate to catastrophic.
Michael Hiles President,
Field Management Services