How grounding practices on USA distribution circuits produce magnetic fields
We explain on our main page on low-voltage distribution that magnetic fields arise when the neutral is earthed in more than one place. This allows the current to divert out of the neutral conductor and creates a "net current". We explain here how this happens, specifically, in USA distribution systems.
Distrubution wiring in the USA typically has small transformers, fed from a primary circuit, and supplying just a few homes. Each transformer produces two "hot wires" at 120 V. These two wires plus the neutral go into each home so that appliances can be connected either at 120 V from one hot wire to neutral, or at 240 V between the two hot wires.
The neutrals of the primary and secondary are connected together and grounded at the transformer. Each home has a ground bus. This is connected to the neutral conductor and also usually to two other grounds - a driven ground rod, water pipes, or structural steel.
This means the neutral is multiply grounded and net currents are created, which are a source of magnetic field.