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Hi 7 3 MONTANA LEGISLATIVE COUNCIL LIBRARY MAGNETIC FIELD MEASUREMENTS IN THE STATE CAPITOL HELENA, MONTANA Prepared for Mr. Gene Braun Manager, Engineering Services Montana Power Company 40 East Broadway Butte, Montana 59701 by Dr. Daniel N. March, P.E. 8/10/93 4 M 4 -M-M ■ 4-4-4- 4 -4—4 *4-4 H I \ -4-f M M M U MARCH ENGINEERING, INC. 9220 Hodgeman Canyon Drive BOZEMAN, MT 59715 (406) 587-2552 f \ / » INTRODUCTION Meter and Protocol On July 19 through 22, 1993, measurements of 60Hz magnetic fields were made in virtually every room on the first three floors of the state capitol. The measurements were made by Dr. Daniel March, a registered professional engineer and professor of electrical engineering at Montana State University. The meter used was a Power Frequency Field Meter, model 111 (Serial # 111-3-28) made by the Electric Field Measurements Co. of West Stockbridge, MA. The instrument is capable of measuring both electric and magnetic fields. The accuracy of the instrument had been checked using laboratory quality equipment on 6/10/93. The meter read the correct values of the 60Hz magnetic fields within two percent. The instrument does respond to other extra-low-frequency fields but it is not calibrated. Generally there were three people involved with the magnetic field measurements. Dr. March made the measurements. A Department of Administration General Services man, either Steve Wilson or Tim Popp, recorded data and lead the team to the rooms in the capitol. Mr. Al Crum from the Helena office of Montana Power helped identify wires, measured currents, and explained the electrical system. Everyone in the capitol was very cooperative. The work was significantly helped by Debra Fulton and Jack Campbell from the office of General Services. Dr. March has measured magnetic fields in offices throughout the state of Montana and has developed a protocol (process) to follow when making such measurements. This was followed in the capitol. Basically a measurement was made in the center of each office and in the middle of each wall. The wall measurements, as well as the measurement at the center of the room, were made at an elevation of one meter above the floor. The wall measurements were made at approximately twelve inches from the wall. The magnetic field was also measured in each office where a person sits at a desk. This measurement was usually not made at an elevation of one meter. The measurement was made 6 to 8 inches from the desk or computer keyboard and at a height a few inches above the desk or keyboard (generally about 32 inches above the floor). In some offices there were many desks with people using each of them. Measurements were made at each desk. The magnetic field meter measures the field in terms of amps/meter which is a term unfamiliar to most people. To convert the readings to milligauss the numeric value measured in amps/meter has to be multiplied by 12.5. Thus an initial measurement of 0.5 amps/meter corresponds to 6.3 milligauss. The data recorded at the capitol . . has been converted to milligauss for presentation in this report. The data has been rounded-off to the nearest tenth of a milligauss with a half of a tenth being assigned the next higher value, i.e. 6.25 was rounded-off to 6.3 in the example above. Electric Fields Electric field measurements were made at several sites in the capitol. The units of electric field are volts/meter. The electric field can easily be stopped with shielding of the wires or by shielding a room with metal. A house under a power line will have no electric field in it due to the line if the attic has fiberglass insulation with metal backing. If all the wires in an area are in metal conduit there is no resulting electric field due to the wires. When the electric fields were measured in the capitol the levels were so low that the readings were in the noise level of the meter. At no time was an electric field found with magnitude greater than 3 v/m, a low level. Due to overhead electric heating in the author's house the average electric field in his home is 30 v/m. The scientific community has found no evidence that electric fields may be hazardous to health(1). In the early days of EMF health concerns there was research into the effects of both electric and magnetic fields. These days most research deals only with magnetic fields. No electric field values are reported in the data section of this report. Magnetic Fields The 60Hz magnetic field is generated by electrical current flow in a conductor. The field produced has a circular pattern about the wire and its magnitude is proportional to the amount of current (in amps) and is inversely proportional to the distance from the wire. Thus the farther one is from one or more wires producing a magnetic field, the smaller the field. There are several properties of magnetic fields that are of interest when considering the fields in the capitol. Magnetic fields are vector quantities such that equal and opposite fields will cancel. If the two wires carrying current to a device, for example an electrical heater, are close to each other the magnetic fields from the two wires, which are carrying equal and opposite currents, will nearly cancel. If the two wires are separated by two or three feet the magnetic fields will not cancel well and there will be a (1) An exception to this is the shock a person gets when touching a grounded piece of metal when the electric field is on the order of 1000 v/m. The author has been in homes where this was the case and the startling effects of the shocks were obvious. 2 ' * . higher magnetic field in the vicinity. High voltage distribution lines feeding buildings generally have low levels of current and generate small magnetic fields. Metal conduit around wires which are carrying equal and opposite currents, like the current to and from a heater, dramatically reduce the magnetic fields. Recent tests have shown that the conduit reduces the magnetic field by approximately 90%. Metal conduit around wires which are not carrying equal and opposite currents does not reduce the magnetic field due to the net imbalance current. That is, if in a conduit covered pair of wires, the current in one direction is 10 amps and the current in the other direction is 6 amps, then the magnetic field some distance from the conduit will be that due to 4 amps. Cable raceways like those in the ceiling of the main hallway in the basement of the capitol do not reduce the magnetic fields from the conductors they contain. In the capitol magnetic fields were found that were caused by a variety of current carrying sources. In many offices, especially on the first floor, magnetic fields were due to wires in the ceiling of the basement. These wires were either not in conduit, or had high current levels, or they were in conduit but did not have equal and opposite currents. In several cases we investigated the nature of the wires in the basement ceiling. Some are in conduit, some are in raceways, some of those in conduit do not have equal and opposite currents, and some are not in conduit. Some Reference Levels The author has made measurements in offices in Billings, Bozeman, and Great Falls. Some of these offices had no nearby high voltage electrical lines and the magnetic fields in the offices were due to building wiring and electronic equipment. Magnetic field levels in buildings with good wiring are typically one to two milligauss. Magnetic field level measurements in a fairly old Bozeman school showed average center of classroom field levels of 7.2mG and a maximum center of classroom level of 16.4mG. The school has been retired for other reasons. A new Bozeman school has an average center of classroom value of 0.12mG and a maximum center of classroom value of 0.4mG. All the school magnetic field levels were measured during school time and in the winter. The author's nine year old house on the outskirts of Bozeman is not near a power line and it is 150 feet from the distribution line. It is an all electric house. Magnetic field measurements in the house when few appliances were operating showed levels in all rooms 3 Digitized by the Internet Archive in 2018 with funding from Montana State Library https://archive.org/details/magneticfieldmea1993marc