Hipot and Dielectric Withstand Testing

Hipot and Dielectric Withstand Testing with TofuPilot

Hipot (high-potential) testing verifies that a product's electrical insulation can withstand voltage stress without breakdown. It's required by UL, IEC, and most safety standards for any product connected to mains power. TofuPilot logs every hipot result for production traceability and compliance.

What Hipot Testing Verifies

Hipot testing applies a high voltage between isolated circuits (typically line-to-ground or primary-to-secondary) and measures the leakage current. If current stays below the threshold and no breakdown occurs, the insulation is adequate.

Parameter	Typical value	Standard
Test voltage (AC)	1000-3000 Vrms	IEC 60950, IEC 62368
Test voltage (DC)	1414-4243 Vdc	IEC 60601 (medical)
Duration	1-60 seconds	Varies by standard
Leakage current limit	0.5-10 mA	Varies by product class
Ramp time	0.5-3 seconds	Prevents voltage spikes

Automating Hipot Tests

Connecting to a Hipot Tester

Most programmable hipot testers (Chroma, Associated Research, GW Instek) support SCPI commands over GPIB, RS-232, or LAN.

hipot_test.py

import pyvisa
from tofupilot import TofuPilotClient

rm = pyvisa.ResourceManager()
hipot = rm.open_resource("GPIB::5::INSTR")
client = TofuPilotClient()

def run_hipot_test(serial, test_voltage_v=1500, duration_s=60, leakage_limit_ma=5.0):
    # Configure hipot tester
    hipot.write(f"VOLT {test_voltage_v}")
    hipot.write(f"TIME {duration_s}")
    hipot.write(f"CURR:LIM {leakage_limit_ma}")
    hipot.write("RAMP 2")  # 2 second ramp

    # Run test
    hipot.write("TEST")
    hipot.query("*OPC?")  # Wait for completion

    # Read results
    result = hipot.query("MEAS:RES?")  # "PASS" or "FAIL"
    leakage = float(hipot.query("MEAS:CURR?")) * 1000  # Convert to mA

    passed = result.strip() == "PASS"

    client.create_run(
        procedure_id="HIPOT-SAFETY-TEST",
        unit_under_test={"serial_number": serial},
        run_passed=passed,
        steps=[{
            "name": "Dielectric Withstand",
            "step_type": "measurement",
            "status": passed,
            "measurements": [
                {"name": "test_voltage_v", "value": test_voltage_v, "unit": "V"},
                {"name": "duration_s", "value": duration_s, "unit": "s"},
                {"name": "leakage_current_ma", "value": leakage, "unit": "mA", "limit_high": leakage_limit_ma},
                {"name": "breakdown", "value": 0 if passed else 1, "unit": "bool", "limit_high": 0},
            ],
        }],
    )

    hipot.write("VOLT 0")  # Discharge
    return passed

Multi-Point Hipot Testing

Some products require hipot tests between multiple isolation boundaries.

multi_point_hipot.py

# Test multiple isolation boundaries
isolation_tests = [
    {"name": "Line-to-Ground", "voltage": 1500, "limit_ma": 5.0},
    {"name": "Line-to-Secondary", "voltage": 3000, "limit_ma": 5.0},
    {"name": "Secondary-to-Ground", "voltage": 500, "limit_ma": 1.0},
]

steps = []
for test in isolation_tests:
    # Configure and run each test
    leakage = run_hipot_measurement(test["voltage"])
    passed = leakage < test["limit_ma"]

    steps.append({
        "name": test["name"],
        "step_type": "measurement",
        "status": passed,
        "measurements": [
            {"name": f"voltage_{test['name'].lower().replace('-', '_')}", "value": test["voltage"], "unit": "V"},
            {"name": f"leakage_{test['name'].lower().replace('-', '_')}", "value": leakage, "unit": "mA", "limit_high": test["limit_ma"]},
        ],
    })

all_pass = all(s["status"] for s in steps)
client.create_run(
    procedure_id="HIPOT-MULTI-POINT",
    unit_under_test={"serial_number": serial},
    run_passed=all_pass,
    steps=steps,
)

Leakage Current Trending

Even for passing units, track leakage current over production. A healthy process shows consistent leakage values. Changes indicate:

Trend	Possible cause
Gradual increase	Contamination buildup on PCB, flux residue
Step increase	New board revision, different conformal coating
High variance	Inconsistent manufacturing (solder splash, debris)
Bimodal distribution	Two different PCB suppliers or manufacturing lines

TofuPilot's measurement histogram for leakage current shows these patterns across your production.

Compliance Records

Safety agencies require per-unit hipot test records. TofuPilot stores:

Serial number of the tested unit
Test voltage applied
Duration of the test
Measured leakage current
Pass/fail result
Timestamp
Station/tester identification

When an auditor asks for hipot records for a specific serial number or date range, pull them from TofuPilot in seconds.

Safety Considerations

Hipot testing involves lethal voltages. Always:

Use proper safety interlocks on the test fixture
Ensure the DUT is fully discharged after the test
Never bypass safety mechanisms on the hipot tester
Log test equipment calibration dates
Train operators on hipot safety procedures

TofuPilot is the data management layer. The safety of the test setup is your responsibility.

Ground Continuity Testing

Ground continuity is often tested alongside hipot. It verifies that the safety ground connection has low enough resistance to carry fault current.

ground_continuity.py

# Ground continuity test (typically 25A for 2 seconds)
ground_resistance = measure_ground_resistance(current_a=25, duration_s=2)

client.create_run(
    procedure_id="GROUND-CONTINUITY",
    unit_under_test={"serial_number": serial},
    run_passed=ground_resistance < 0.1,
    steps=[{
        "name": "Ground Bond",
        "step_type": "measurement",
        "status": ground_resistance < 0.1,
        "measurements": [
            {"name": "ground_resistance_ohm", "value": ground_resistance, "unit": "ohm", "limit_high": 0.1},
            {"name": "test_current_a", "value": 25, "unit": "A"},
        ],
    }],
)

Most safety test workflows run ground continuity first, then hipot. If the ground bond is bad, there's no point running the hipot test. TofuPilot links both results to the same serial number for a complete safety test record.

Hipot and Dielectric Withstand Testing