In some instances, it is possible to make changes to wiring configurations to enhance natural magnetic field cancellation between individual conductors in an electrical circuit. In nearly all AC power distribution circuits, naturally emitted magnetic fields, can be dramatically reduced if:
All conductors in the circuit are arranged or bundled tightly together and/or are arranged in an optimum relationship
If opposing currents (as in a phase and neutral) are equal.
Net or ground current paths are not present.
This technique is often employed by utilities in the design of high voltage transmission and distribution lines to reduce EMF levels in nearby buildings. In rare instances, it is also possible to achieve significant reductions in AC magnetic field levels usually present in areas adjacent to large utility transformer vaults, by replacing widely spaced interconnecting bus bars with cables arranged close together.
In some instances, wiring errors in a building can create "Net-Current" conditions which can cause elevated AC magnetic fields over a large area which are very difficult to shield. When a building's wiring is installed according to the National Electric Code, electrical current goes out and returns on the same circuit path (phase and neutral). If certain types of wiring errors are made which create alternative paths for the return current from a circuit, a condition results commonly referred to as a "Net Current".
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