COMED Transformer Vault - Chicago

In August 2003, VitaTech Engineering conducted an AC extremely low frequency (ELF) site survey within the office spaces above a 25th floor COMED transformer vault for a realty service located in Chicago, Illinois. Elevated magnetic flux density data levels were recorded and analyzed indicating that circulating ground/net currents were present and contributing to the lack of normal decay of the magnetic fields. An electrical remediation project was conducted in September 2003, uncovering numerous N.E.C. wiring violations and grounding problems. Subsequently, recommendations were made to install a 6,996 ft2 magnetic shield inside the 25th floor COMED vault to provide attenuation from the magnetic fields emanating into the adjacent office area on the above floor. The objective of this report was to verify compliance of the performance specifications measured 1-meter above the shielded space.

Low (1 - 9.99 mG), elevated (10 - 99 mG), and high (100 - 450 mG) AC ELF magnetic flux density levels were recorded during the original site survey and again during electrical remediation. The strongest fields (450 mG) were recorded on the floor directly over the second bank of transformers . On November 14th - 23rd 2003 (weekends only), VitaTech installed the 6,996 ft2 (surface area) shield composed of conductive seam welded aluminum and low-carbon steel plates. A performance/compliance survey was conducted after the shielding installation was completed. The AC ELF magnetic shield complies with the performance guarantee as required.

Before AC Shielding:

After AC Shielding: