Well its been almost a year, and we finally moved the rest of the company into this building.
I still have concerns about the ability of the grounding paths to handle any significant fault currents.
My thought is to test the resistance of the ground paths by using a welder to supply a controlled current of 100-200 Amps for a few seconds between the subpanel ground bar and the building's service bonding location and then measuring the voltage drop between the subpanel ground bar and the building's central ground.
Obviously this would have to happen with the subpanel deenergized, along with suitable Kelvin connections to ensure we are only measuring the voltage drop along the ground path and not the v drop across the welder to ground bar connection. Also we would need enough people to look for unexpected arcs or excessive heating across any high resistance ground paths.
Assuming I can get permission to perform these tests, what would be an acceptable range of voltage drops?
Larry
