I have a house with a 600 amp service panel and 4 subpanels. I have taken readings on the equipment grounding conductor and they read between 0.2 amps and 0.8 amps. We physically checked that there were no neutrals tied to equipment grounds. We found 5 issues and corrected. This did not affect the reading. One thing I noticed is that the grounds from all the panels were tied together, not just at the main grounding bus but through the #12 equipment ground junction points where 2 circuits from different panels occupy the same box. Secondly, I noticed that as the any load was increased or reduced on the whole system, the amperage on the ground increased and decreased proportionally. Thirdly, one of the sub-panels feeds a pool with a rebar shell as its equipotential bonding plane. Any thoughts on why the equipment ground shows amperage? Is this normal? I would think it should be zero but I am starting to wonder.
The most likely explanation is that you have one neutral to ground wire connection at the service box and there is another neutral to earth connection at the utility transformer secondary.
That means that for the normal neutral current in the house (coming from the imbalance between the loads on L1 and the loads on L2) there are two parallel paths. One goes through the service neutral wire to the transformer (fractional ohm resistance, hopefully) and the other path goes through your grounding electrode conductor (not EGC) to the ground electrode(s), through the earth to the utility ground rod and up to the transformer secondary neutral.
The latter path has a much higher resistance, which is why such a small percentage of the total neutral current flows through it.
This is normal for the way the NEC and POCO handle the service, and is actually small compared to what some homeowners have when one of the ground electrodes is a water pipe.
Again, since you talk about just one of them, I am assuming that by Equipment Grounding Conductor (EGC) you really mean the single Ground Electrode Conductor (GEC) at the service panel.
