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Wiring Error Investigation

Wiring errors, sometimes even seemingly minor ones, can create “Net-Current” conditions which can cause elevated magnetic fields over a large area.

(Typical magnetic fields from a transformer vault, for example, fall off relatively quickly with distance, however, these fields do not.)

When a building’s wiring is installed according to Code (National Electric Code), current goes out and returns on the same circuit path, maximizing the natural cancellation of magnetic fields from electric currents. If, in the course of the electrical distribution system of a building, certain types of errors are made which create alternative paths for the return current from a circuit, a situation results which is commonly referred to as a “Net Current”.


The consequence of these errors, in addition to being violations of Code and posing both fire and shock hazards, is that the fields which result are both larger and decay more slowly that conventional “separation” fields. Conventional shielding is inefficient when combating net-current conditions. Instead, correct engineering practice requires that the wiring errors must be isolated and corrected prior to consideration of any other mitigation options, including shielding.

FMS offers Wiring Error Investigation services and typically works with a local electrician or contractor of the Client’s choice to isolate and correct Code violations. Detailed and systematic measurement of the electrical systems can point our specialized engineering staff to a speedy and accurate resolution of the problem.

Recent Projects

Dana Farber Cancer Institute

FMS was engaged to conduct a thorough assessment of the building’s design for EMI interference threat concerns to sensitive clinical and research equipment.

85 Broad Street

To mitigate EMI threat concerns, FMS designed and implemented multiple special magnetic field shielding schemes to lower EMF levels to acceptable, non EMI threat levels.

National Renewable Energy Laboratory

As the EMI Consultant, FMS performed an assessment of the potential for large power distribution systems to impact the operations of sensitive imaging tools and other susceptible electronic equipment.


Over its 20 years, FMS has successfully completed hundreds of EMI projects which included a diverse range of consulting and mitigation services.

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