Hi Russ, thank you for your question regarding electrical currents on your Equipment Ground Conductor (EGC). It is our pleasure to help.
In a properly grounded system you should not see electrical currents higher than a few milliamps on the EGC, certainly no greater than 1/2 an amp. Even in very large grounding systems with circulating currents, it is rare to see currents exceeding these levels (when they do, it indicates an inadequate grounding electrode system). That said, there are cases where higher currents might be found such as in a high-voltage environment. For example, transmission towers carrying 66kV to 500kV power lines, often have a steady-state Ground Potential Rise (GPR) due to the magnetic fields of the lines, resulting in induced-currents that often exceed 5-amps. This is considered normal in these situations. However, if you are simply talking about an EGC on a 480-volt (Wye) or less system, you should see very minimal currents on the EGC.
If you do have higher currents, it typically indicates an improper neutral-to-ground connection somewhere in the system. Trouble shooting these issues can be difficult, as the problem could occur at the transformer’s XO connection, or it could be at a sub-panel, or any number of other points in the system. It could also indicate a fault and a failed Over Current Protection Device (OCPD). If your system is 3-phase Delta, stray current on the EGC could indicate a serious fault is occurring, and should be checked out by a qualified electrician right away.
Another issue to be cautious of, is improperly installed isolated grounding electrodes. In certain situations, isolated grounding electrodes installed in violation of National Electrical Code (NEC) Article 250.58 Common Grounding Electrode, will be at a different potential than the rest of the grounding system and can have unwanted currents, and cause OCPD’s to fail.
We hope you find this information helpful, and good luck!
The E&S Grounding Solutions Engineering Team
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