130525-1152 EDT
In my area there are a great number of 3 wire 3 phase primaries with 2 post primary transformers to supply the load. Here the residential neutral, secondary side, is only associated with the pole transformer and earth in at least two places. There will be very little current in this neutral that flows back to the sub-station. There may be neutral current from different homes on the same transformer that result from ground rod paths, water pipes, and other conductive paths between homes. Transformer neutral current inside the transformer is only related to the transformer. Outside of the transformer the neutral from the transformer to the home may carry a small current from some other source, or local path.
There are also a lot of residential areas with single post single phase transformers. Here the neutral of the primary and secondary are connected together, and some primary neutral current may, and almost certainly will, flow thru the neutral from the transformer to the home. The power company primary neutral has many ground points, and the home has at least one grounding point. This is why primary neutral current shows up on the secondary neutral. Once you pass the home main breaker panel there should not be any primary neutral current flow.
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