Electrical Wiring Problems
and High Magnetic Fields

The Problem of Mis-Wired Electrical Circuits

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), such as electrical noise in recording studios, 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 imbalance problems. The personnel of EMF Services have over 32 years experience in the correction of electrical wiring errors, in everything from high-rise buildings to recording studios to homes.

How Wiring Errors Create High Magnetic Fields

Here is a basic explanation of how an elevated magnetic field is produced by a circuit imbalance. Most of the wiring in homes and commercialbuildings 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. 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.

Common Types of Wiring Errors

• Neutrals from separate branch circuits that are connected anywhere beyond the point of origin


• Neutral-ground shorts (intentional or inadvertent) anywhere in the system


• 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

Electrical Code Violations

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.

Photos of Electrical Wiring Problems
that Create High Magnetic Fields