An acceptance test for a ground-fault protection system in a low-voltage installation verifies that the protective relay, current-transformer or rogowski-coil sensor, and control wiring are correctly installed and functional before the system is put into service. The test captures the system voltage and control voltage from the nameplate or as-built drawings, records the sensor or current-transformer ratio, checks the insulation resistance of the control wiring to ground, and confirms that the relay responds correctly to a simulated ground-fault current injected at the sensor without spurious operation. NETA ATS-2025 7.14 lists the test items and acceptance criteria for ground-fault schemes protecting switchboards, transfer switches, motor-control centers, and other low-voltage apparatus.
A ground-fault relay that is wired incorrectly, miscalibrated, or installed with a damaged sensor will fail to detect a ground fault when one occurs, leaving personnel and equipment unprotected, or it may nuisance-trip on harmless transients and disable a critical circuit. Before the system is energized and relied upon, acceptance testing confirms that the relay responds to a known fault signal at the expected sensitivity threshold, that the sensor is installed in the proper location with the proper turns ratio, and that the control circuit will carry the trip signal to the breaker or contactor without degradation. Testing before first energization catches installation errors, loose connections, and sensor mismatches that could otherwise go undetected until a real ground fault occurs - at which point the relay's response (or failure to respond) could be lost to the field situation.
Acceptance: run on a new or reconditioned ground-fault system before the protected apparatus is first energized, as part of the switchboard, transfer switch, or motor-control-center electrical test sequence. The test includes a functional checkout of the relay's response to the simulated fault and a confirmation that the control wiring insulation is sound so the trip signal will not be diverted to ground if a secondary fault occurs.
With the protected apparatus de-energized and the ground-fault relay in service mode (or the mode into which it will be placed when the apparatus is energized), the control wiring is tested for insulation resistance between the relay terminals and ground at the test voltage specified in NETA ATS-2025 7.14, held for the specified duration. Separately, the relay's response is verified by injecting a known current signal at the sensor terminals (or by applying voltage to a test jack if the relay and sensor are combined in a single package) that simulates a ground fault, and confirming that the relay output transitions to trip the breaker. The injected current is typically set to a value that equals the nameplate pickup threshold of the relay, or is ramped up slowly so the technician can observe the exact current at which the relay transitions, then recorded for the acceptance report.
System voltage, control voltage, sensor or current-transformer ratio, test voltage and duration for control-wiring insulation resistance, insulation resistance measured value for control wiring to ground, injected current at which the relay trips (and the relay model and nameplate pickup setting for reference), and test-instrument identification (make, model, serial, calibration due date). Observations on sensor installation, wire routing, and any mechanical damage to the relay housing or connectors are captured as well.
NETA ATS-2025 7.14 specifies an insulation-resistance minimum for control wiring to ground and a tolerance band around the nameplate relay pickup threshold for the functional trip test. The control wiring result must meet a specified minimum (often 1 megohm or higher, depending on voltage class, per the purchased standard) so that a secondary ground fault in the control circuit will not disable the trip signal. The relay's response current must fall within the nameplate pickup setting by a tolerance defined in the standard; a relay that trips at a current significantly higher or lower than the setting is flagged for troubleshooting - typically a sensor wiring error, a misconfigured relay parameter, or a defective sensor - before the apparatus is energized. See the purchased NETA standard for the complete acceptance table and voltage-specific criteria.
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