The importance of checking the electrical installation under load with a gaussmeter before occupancy is demonstrated in this case study. An electromagneticallysensitiveclient consulted with John by telephone throughout the construction of her home, which was built according to specifications similar to those outlined in this book. After the client moved into her new home, she began experiencing symptoms that occur when she is exposed to elevated magnetic fields, such as ringing in the ears and inability to concentrate. Using a gaussmeter, she discovered that about half of the home registered over 5 milligauss. She called John in a state of panic, convinced that her house was ruined and that she would never be able to live in it.
John contacted the client’s electrician and offered to help him diagnose the problem over the
telephone. Under John’s guidance, the electrician conducted field testing with the client’s gaussmeter. From the measurements, it became clear to John that the problem was located in the subpanel controlling a section of the house. At that point, the electrician immediately realized what he had forgotten to do. Some panels and subpanels are interchangeable except for a single screw that must be removed from the neutral bus bar to electrically isolate it from the ground wires in the panel. Called a bonding screw, it was causing net current in all circuits in the subpanel. The electrician simply removed the bonding screw and the magnetic fields dropped in an instant to less than 0.2 milligauss.
detected throughout the structure before it is energized, there is reasonable cause to suspect that fields are entering from an outside source. At this point, consult an expert who can properly block them. Because neighborhood conditions may change over time, fields should be checked regularly.
Along with proper bonding and grounding, grouping the entry points of all utilities will also provide more protection against lightning damage. However, this is not a substitute for lightning rods and lightning surge protection, which are designed to protect the home during a lightning storm.
The following are specifications for preventing the entry of magnetic fields through utility services:
• All utilities, including telephone, cable TV, gas, and water, shall enter the building at approximately the same location, within a four-foot radius.
• All utilities entering the structure shall be properly bonded immediately prior to entry in accordance with the National Electrical Code (NEC).
• Bonds or grounds shall occur at only one point along each utility in accordance with the NEC.
• All utilities shall be tested with a gaussmeter when the house power is turned off. If magnetic fields are detected, inform the owner or architect immediately.
