Electromagnetic fields
in buildings and structures

The use of electricity results in the production of power frequency electric and magnetic fields. These fields are not only associated with overhead or underground power lines but also electrical wiring systems that distribute power within buildings and homes. A number of projects carried out by Richard Tell Associates have been directed toward characterizing the electric and magnetic fields in the interior of commercial office buildings and factories. The concept of how these fields may be distributed throughout a building structure is illustrated in this simplified drawing of the electrical anatomy of a building.


A common finding in these studies is the presence of strong magnetic fields near the electrical switch gear for the building. This is often the case because of the fact that all of the electrical power for the facility normally enters the building through a single electrical room, typically in the basement, and is distributed to other parts of the building through heavy duty switch panels. While the incoming utility power may be contained within cables, the individual current carrying conductors are generally spread apart on the interior of the switch apparatus leading to considerably stronger fields due to less phase cancellation.

A common scenario is for outside utility power to enter the bottom of the switch panels from beneath (but not always) and to exit the panels from the top, whereupon it is distributed via either cables contained within large electrical conduits or via bus bars. It is interesting to note that bus bars generally lead to greater magnetic fields in their vicinity than cables carrying the same currents simply because of the greater separation of the conductors, again reducing the phase cancellation effects afforded by tightly configured bundled cables.


In some cases, unbundled, very high current carrying cables may be used to distribute electrical power through an industrial facility for operating high power test equipment. These cables, such as when attached to the ceiling as shown here, can produce magnetic fields over an extended region.