The grounding-system acceptance test verifies that the engineered network of conductors, rods, plates, and interconnecting mesh or cables that connect every energized component and every metallic structure in a facility back to earth (or to a defined remote-earth reference) has been installed per drawing and specification, and that every critical path through the system carries current with acceptably low resistance. NETA ATS-2025 7.13 specifies two complementary field methods. The resistance of the main grounding electrode system to remote earth is measured using the fall-of-potential method described in IEEE 81, in which temporary current and potential probes are driven into the earth at increasing distances from the electrode system to determine the electrode's true resistance to a remote-earth reference. Separately, point-to-point resistance is measured between defined pairs of bonded ground points - for example, from a building steel frame to a driven rod, from a transformer neutral ground to main switchgear, or from one section of a ground grid to another - using a four-terminal (Kelvin-clamp) ground tester so the measurement excludes the test leads' own resistance. For these point-to-point paths, the test set drives a known AC current (usually at line frequency or a nearby frequency) and measures the voltage drop across the path, then calculates and records the resistance in ohms.
A grounding system's job is two-fold: to provide a low-impedance path for fault current so it flows to earth rather than through people or equipment, and to establish a voltage reference (typically called ground potential) that keeps all energized conductors at a predictable potential relative to earth. If the installed ground system deviates from the design - missing connections, corroded joints, incomplete conductors, or wrong gauge wire - the actual resistance will exceed the engineered value, fault currents will not be what the protective relays were calibrated to see, and the ground potential will rise unevenly during a fault, creating a touch-voltage or step-voltage hazard. Confirming the network before it is put into service means the system will perform as designed rather than discovered by failure.
Acceptance: performed on new grounding systems or major system upgrades before the facility (or the upgraded section) is first energized, as part of the baseline electrical test suite. Maintenance: repeated on a periodic interval per the owner's maintenance plan, or triggered by work on the grounding system itself (rod or conductor replacement, subsurface digging that might have severed a path, or a major repair to a joint or connector). The acceptance baseline is kept on file so each maintenance test can be compared to the as-built values and trended for degradation.
With the electrical system de-energized and the grounding network isolated from any ongoing energization, the main grounding electrode resistance is measured first: auxiliary current and potential probes are driven into the earth in line with the electrode system at progressively greater distances, per the fall-of-potential method in IEEE 81, until the measured resistance stabilizes to a value representing the electrode system's true resistance to remote earth. The test technician then sets up the four-terminal ground-resistance tester at the first point-to-point measurement pair. The current lead (often the generator terminal) is connected to one ground point, the return lead to the second, and the voltage-sensing leads (which carry negligible current) are clamped at intermediate points on the same two paths so they measure only the voltage drop across the actual conductor, not the test leads. The tester drives current and reads resistance, and the process repeats for each specified path in the system. All measurements are taken with the system at ambient temperature and documented with test-equipment identification, date, location, and path description so the result can be reproduced and compared later.
The main grounding electrode's measured resistance to remote earth in ohms, the test method used (fall-of-potential or an alternative IEEE 81 method), and any owner-specified limit. For each point-to-point path tested: the starting point and ending point (by drawing reference, location, or equipment name), the measured resistance in ohms, the ambient temperature, the system type if applicable (large commercial or industrial facility, generating or transmission station, or owner-specified alternative), the test equipment make, model, serial number, and calibration-due date, and any notes about site conditions, corroded connections, or deferred work.
NETA ATS-2025 7.13 establishes two distinct kinds of acceptance criteria. The main grounding electrode's resistance to remote earth is evaluated against a maximum limit that varies by facility type - a looser limit applies to large commercial or industrial systems than to generating or transmission stations - unless the owner specifies a tighter limit, per the IEEE 142 guidance the standard references; consult the purchased standard for the specific values. Point-to-point resistance paths, by contrast, are evaluated as path-specific engineering tolerances set by the design drawing or specification rather than as one universal limit: for each point-to-point resistance path, the measured value must fall within the design tolerance band (if specified on the drawing) or, if no tolerance is given, must not exceed the value stated in the system design standard for that facility type or voltage class. The evaluation compares the measured resistance against the engineered expectation, not an arbitrary threshold; a path reading significantly higher than specified warrants investigation of that particular connection or conductor before acceptance. See the purchased standard for the complete evaluation framework, the specific path configurations and electrode-resistance limits it covers, and any system-type exceptions.
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