High magnetic field environments are created more frequently
by electrical and grounding system problems than by any other source. This is true in both residential and
commercial buildings. The problem usually results from unbalanced and improperly wired feeders
and branch circuits. The elevated magnetic fields that result from this imbalance can be a source
of electromagnetic interference (EMI) or concern over human health effects.
Since these wiring problems usually manifest no overt functional
deficits in the electrical system, they often escape notice, but they are immediately
apparent when an AC magnetic field meter is used. In areas (or entire buildings) where such problems
exist, magnetic field levels are dramatically higher. Readings of 5 -20 mG (milligauss) are not uncommon, and occur
whenever the circuits involved are in use (and with some problems, even when they are not). Fortunately,
these conditions are fully correctable. The problem must be traced out, located, and rewired in a proper
and code compliant manner. Conventional magnetic shielding with metal plates is ineffective for current
Here is a basic explanation of how an elevated magnetic field is
produced by a circuit imbalance. Most of the wiring in homes and commercial
buildings consists of cables containing two or more current-carrying conductors (or conduits
containing multiple conductors). At any point in time, an equal current is flowing
in one direction on one wire, and in the opposite direction on another wire.
Since these wires are very close together inside the cable jacket or conduit,
the magnetic field around one wire is cancelled by the opposite magnetic field
around the other wire. The field drops to a negligible level a few inches from the wires. In this
case there is no net current on the circuit, and a clamp-on ammeter placed around
the cable or conduit will indicate zero current.
Problems occur when this balance is destroyed by improperly wired
circuits. Common examples are:
improperly wired subpanels (a form of N - G short)
incorrect three-way switch wiring where the hot and neutral are fed to different points in the circuit
neutral-ground shorts (intentional or inadvertent) anywhere in the system
- neutrals from separate branch circuits that are connected anywhere beyond the point of origin
In each case, a portion of the normal utilization current is caused to flow over an alternate path, creating
an imbalance, or net current, on two or more circuits. A clamp-on ammeter placed around the cable or
conduit of such a circuit will indicate a substantial current (often 1 to 10 Amps). It is not unusual to find
multiple wiring errors in new construction, and inspections conducted by local code enforcement authorities will
not detect the great majority of these problems.
Although most types of electrical code violation do
not create elevated magnetic fields, virtually all wiring errors that create high
fields are code violations, usually of NEC Articles 250.24(A)(5), 250.142(B), and 300.3(B)(1).
Thus, there is a solid rationale for correcting and avoiding these common problems which extends beyond
magnetic field reduction. Any site survey should be conducted in a manner that will detect and document them. The
personnel of EMF Services have extensive experience in the correction of electrical wiring errors.
All problem resolution services are delivered by an IAEI certified electrical inspector or a licensed electrical
contractor, each with over 23 years of EMF remediation experience.
Photos of Electrical Wiring Problems
that Create High Magnetic Fields