The hipot test procedure (High Potential or Dielectric Withstand test) is a critical safety verification step that stresses electrical insulation with high voltage to ensure no current leaks to the chassis or user-accessible parts. Unlike continuity or functional testing, this process deliberately applies voltages far exceeding normal operation—typically 1000V to 5000V—to identify marginal insulation, pinholes, or spacing violations before a product reaches the market.

Key Takeaways

• Core Definition: A stress test applying high voltage (AC or DC) between current-carrying conductors and the non-current-carrying ground to verify isolation.
• Standard Formula: The baseline test voltage for many consumer electronics is $2 \times V_{operating} + 1000V$.
• Duration Rule: Type testing (R&D) typically requires 60 seconds, while production line testing is often reduced to 1 to 2 seconds to maintain throughput.
• Leakage Threshold: A passing unit must maintain leakage current below a set limit, typically ranging from 0.5 mA to 5 mA, depending on the safety standard (e.g., UL 60950, IEC 62368).
• Safety Critical: Always verify the safety interlock system and ensure the "Return" cable is grounded before touching the High Voltage (HV) probe.
• Misconception: Hipot is not the same as Megger testing; Hipot stresses insulation to the breakdown point, while Megger measures high resistance at lower stress.
• Validation Tip: Use a "verification load" (a resistor of known value) daily to ensure the tester correctly identifies a failure condition before testing real units.

Contents

• What It Really Means (Scope & Boundaries)
• Metrics That Matter (How to Evaluate It)
• How to Choose (Selection Guidance by Scenario)
• Implementation Checkpoints (Design to Manufacturing)
• Common Mistakes (and the Correct Approach)
• FAQ (Cost, Lead Time, Materials, Testing, Acceptance Criteria)
• Glossary (key terms)
• Conclusion (next steps)

What It Really Means (Scope & Boundaries)

The hipot test procedure is the final gatekeeper of electrical safety. While a functional test plan pcb verifies that a board works, and a flying probe test tutorial might explain how to check for shorts at low voltage, the hipot test specifically looks for insulation weaknesses that only appear under high electrical stress.

It operates on a simple principle: if the insulation is sufficient, the high voltage applied between the "Line/Neutral" and "Ground" will result in negligible current flow. If the insulation is compromised—due to nicked wires, insufficient creepage distances on the Printed Circuit Board (PCB), or conductive debris—the current will arc or flow through the defect, tripping the tester.

The Physics of Breakdown

When voltage increases, the electric field strength across the insulation increases. Every insulator has a breakdown voltage. The hipot test applies a voltage lower than the breakdown voltage of good insulation but higher than the breakdown voltage of defective insulation.

• Flashover: An arc across the surface of the PCB or component.
• Breakdown: A puncture through the insulation material itself.

Ac vs. Dc Hipot

• AC Hipot: Stresses the insulation with alternating polarity. It is more aggressive because it tests the reactive capacitance of the device. It mimics mains power stress.
• DC Hipot: Applies a static high voltage. It requires a gradual ramp-up to charge the device's capacitance. Once charged, the only current flowing is the true leakage current.

Metrics That Matter (How to Evaluate It)

To establish a robust hipot test procedure, you must define specific numeric pass/fail criteria. Vague requirements like "test for safety" lead to inconsistent quality.

Table 1: Critical Test Parameters

Metric	Typical Range	Why It Matters	Verification Method
Test Voltage (AC)	1000V – 5000V	Determines the stress level. Too low misses defects; too high damages good units.	Calibrated HV meter.
Test Voltage (DC)	1414V – 7070V	DC equivalent is usually $1.414 \times V_{AC}$ to match peak stress.	Calibrated HV meter.
Ramp Time	0.5s – 5.0s	Prevents current spikes from triggering false failures due to inrush.	Timer on tester display.
Dwell Time	1s (Production) / 60s (Type)	Duration the voltage is held. Longer times detect slow thermal breakdown.	Stopwatch / Tester log.
Leakage Limit	0.1 mA – 10 mA	The threshold for failure. Set slightly above normal capacitive leakage.	Known resistance load.
Arc Detection	Level 1 – 9 (Sensitivity)	Detects high-frequency noise indicating impending arc before full breakdown.	Spark gap simulator.
Discharge Time	< 0.2s	Time required to drain voltage to safe levels (<50V) after test.	Oscilloscope probe.

Table 2: Standard Voltage Requirements

Different industries mandate different voltage calculations.

Standard	Application	Test Voltage Formula	Typical Value (120V Device)
IEC 60950 / 62368	IT Equipment	$2 \times V_{rated} + 1000V$	~1240V AC
IEC 60601	Medical Devices	$2 \times V_{rated} + 1000V$ (Basic)	1500V AC (4000V for reinforced)
IEC 60335	Household Appliances	$2 \times V_{rated} + 1000V$	1240V AC
Class II (Double Insulated)	No Ground Pin	$2 \times V_{rated} + 2000V$	~2500V AC
Component Level	Relays/Optocouplers	Rated Isolation Voltage	3750V - 5000V AC

How to Choose (Selection Guidance by Scenario)

Selecting the right parameters and equipment for your hipot test procedure depends on the Device Under Test (DUT) and the manufacturing environment.

1. If the DUT has high capacitance (e.g., large EMI filters), choose DC Hipot.
   • Reason: AC testing will cause high reactive current flow ($I = V \times 2\pi fC$), which may exceed the tester's current limit even if insulation is good. DC charges the capacitor once and reads only resistive leakage.
2. If the regulatory standard specifies "AC Only," choose AC Hipot.
   • Reason: Some standards do not allow DC substitution because AC stresses the insulation with alternating polarity, which is more representative of actual mains operation.
3. If you need to eliminate "Ramp Down" time, choose AC Hipot.
   • Reason: AC voltage does not charge the device capacitance to a static level, so the DUT is safe to touch almost immediately after the test stops. DC requires a discharge period.
4. If you are testing sensitive electronics that cannot tolerate over-voltage transients, choose DC with a slow ramp.
   • Reason: Controlled ramping prevents overshoot and protects sensitive components from voltage spikes.
5. If you are performing a "Type Test" for certification, choose a 60-second duration.
   • Reason: Certification bodies require a one-minute withstand test to prove design robustness.
6. If you are performing "Routine Tests" on a production line, choose a 1-2 second duration.
   • Reason: High-volume manufacturing cannot afford 60-second cycles. Standards usually allow increasing voltage by 10-20% in exchange for reducing time to 1 second.
7. If the product is Class II (Double Insulated), choose a higher voltage limit (typically 2500V+).
   • Reason: Without a protective earth ground, the insulation barrier is the only safety mechanism and must withstand higher stress.
8. If you see frequent false failures due to humidity, choose to adjust the leakage limit or dehumidify.
   • Reason: High humidity can increase surface leakage current. Do not simply raise the limit without verifying the cause.
9. If testing cables or harnesses, choose a multi-point tester.
   • Reason: You must test isolation between every conductor and every other conductor, which requires automated switching matrices.
10. If the DUT contains components rated lower than the test voltage (e.g., MOVs), choose to remove or disconnect them.
    • Reason: Metal Oxide Varistors (MOVs) are designed to conduct at high voltages. They will trip the hipot tester and potentially be destroyed during the test.

Implementation Checkpoints (Design to Manufacturing)

Implementing a reliable hipot test procedure requires a systematic approach. Follow these 10 steps to ensure safety and compliance.

1. Safety Interlock Setup

• Action: Install a safety enclosure or light curtain connected to the tester's interlock port.
• Acceptance Check: The tester must not start if the enclosure door is open.

2. Ground Integrity Check

• Action: Ensure the tester's chassis is grounded to earth. Connect the "Return" lead to the DUT's metal chassis.
• Acceptance Check: Resistance between tester chassis and facility ground must be < 0.1 Ω.

3. Parameter Configuration

• Action: Program the Voltage ($V_{test}$), Ramp Time ($T_{ramp}$), Dwell Time ($T_{dwell}$), and Current Limit ($I_{trip}$).
• Acceptance Check: Verify settings against the specific UL/IEC standard for the product.

4. Daily Verification (the "Dummy Load")

• Action: Before testing production units, connect a resistor calculated to fail the test (e.g., if 1000V/10mA limit, use a 90kΩ resistor).
• Acceptance Check: The tester MUST indicate "FAIL" and "Leakage High." If it passes the resistor, the tester is faulty.

5. Dut Isolation

• Action: Disconnect any surge protection devices (MOVs, GDTs) or ensure they are rated above the test voltage.
• Acceptance Check: Visual inspection confirms MOVs are removed or jumpers are open.

6. Connection Sequence

• Action: Connect the Low/Return lead first, then the High Voltage lead.
• Acceptance Check: Connections are secure; no loose alligator clips resting on the workbench.

7. Ramp up Phase

• Action: Initiate the test. The voltage should rise linearly over the programmed ramp time (e.g., 2 seconds).
• Acceptance Check: Display shows voltage increasing without overshoot > 5%.

8. Dwell Phase

• Action: Maintain full voltage for the specified duration (e.g., 1 second).
• Acceptance Check: Leakage current reading remains stable and below the $I_{trip}$ limit.

9. Discharge Phase (Dc Only)

• Action: After the test, the tester discharges the DUT capacitance.
• Acceptance Check: Do not touch the DUT until the voltage display reads < 30V.

10. Data Logging

• Action: Record the result (Pass/Fail) and the measured leakage current.
• Acceptance Check: The serial number is associated with the test result in the quality system.

Common Mistakes (and the Correct Approach)

Failures in the hipot test procedure often stem from setup errors rather than product defects.

1. Floating the Return Lead

• Mistake: Leaving the return lead disconnected or poorly connected.
• Impact: The DUT chassis floats to high voltage. The test passes falsely because no current can flow back to the tester, but the operator is at risk of shock.
• Fix: Always use a "Ground Continuity Check" feature if available.
• Verify: Measure continuity between the return clip and the tester chassis before starting.

2. Ignoring Cable Capacitance

• Mistake: Using long, coiled HV cables during AC testing.
• Impact: The cable itself has capacitance. The tester measures the current charging the cable as leakage, causing false failures.
• Fix: Keep cables short and uncoiled. Perform an "Offset" or "Null" calibration with cables open.
• Verify: Run the test with no DUT attached; leakage should be near 0.00 mA.

3. Testing Phase-to-Neutral

• Mistake: Applying HV between the Line and Neutral pins of the power cord.
• Impact: This is a short circuit test, not an insulation test. It will blow the input fuse or damage the power supply.
• Fix: Short Line and Neutral together and apply HV to them simultaneously against the Ground pin.
• Verify: Use a specialized adapter box that shorts L+N automatically.

4. Setting Limits Too High

• Mistake: Setting the trip limit to the tester's maximum (e.g., 20mA) to avoid nuisance tripping.
• Impact: A unit with marginal insulation (e.g., 15mA leakage) passes but is dangerous.
• Fix: Characterize the normal leakage of good units (e.g., 2mA) and set the limit 20-30% higher (e.g., 2.5mA).
• Verify: Analyze statistical distribution of leakage current in a batch of 50 units.

5. Neglecting Ramp Time

• Mistake: Applying full voltage instantly (0 second ramp).
• Impact: Current spikes trigger the "High Current" alarm immediately due to capacitive inrush.
• Fix: Set a ramp time of at least 1.0 second.
• Verify: Observe the current trace on the tester; it should rise smoothly.

6. Re-Testing without Cooling

• Mistake: Repeatedly hipot testing the same unit to troubleshoot a failure.
• Impact: Insulation degrades with repeated stress. A unit that was marginal might become a hard failure due to the testing itself.
• Fix: Allow insulation to recover. Limit the number of re-tests.
• Verify: Track re-test counts in the manufacturing execution system.

7. Using Ac on Dc-Only Components

• Mistake: Using AC hipot on a circuit with Y-capacitors that are only rated for DC testing or have low AC impedance.
• Impact: Excessive leakage current trips the tester.
• Fix: Switch to DC hipot testing for highly capacitive circuits.
• Verify: Check the component datasheets for Y-caps.

8. Touching the Dut During Dc Discharge

• Mistake: Unplugging the DUT immediately after a DC test "Pass" signal.
• Impact: The DUT acts as a charged capacitor (potentially 2000V+). The operator receives a severe shock.
• Fix: Ensure the tester has an automatic discharge circuit and wait for the "Safe" indicator.
• Verify: Measure voltage across the DUT pins immediately after test completion.

FAQ (Cost, Lead Time, Materials, Testing, Acceptance Criteria)

1. What is the difference between Hipot and Dielectric Withstand? They are identical. "Hipot" is an industry slang abbreviation for "High Potential," while "Dielectric Withstand" is the formal term used in standards like UL and IEC.

• Hipot = Common terminology.
• Dielectric Withstand = Formal documentation.
• Both refer to the same voltage stress test.

2. Does hipot testing damage the electronics? A properly configured hipot test is non-destructive to good units. However, it is destructive to bad units; if the insulation fails, the resulting arc can carbonize the PCB, rendering the defect permanent.

• Good units: No degradation.
• Bad units: Permanent failure (which is the goal—to catch them).
• Over-testing: Repeated testing at full voltage can degrade insulation over time.

3. How much does a hipot tester cost? Entry-level manual testers start around $1,500, while automated systems with data logging, multi-point scanning, and AC/DC/IR capabilities range from $5,000 to $15,000.

• Basic (Manual): $1.5k - $3k.
• Programmable (Lab): $4k - $8k.
• Automated (Production): $10k+.

4. Can I use a multimeter for hipot testing? No. A standard multimeter uses a 9V battery to measure resistance, which cannot stress insulation. A hipot tester generates thousands of volts to jump gaps that a multimeter would see as "open circuit."

• Multimeter: Low voltage (<12V).
• Hipot: High voltage (>1000V).
• Megger: High voltage (500V-1000V) but measures resistance, not breakdown.

5. What is the "Arc Detection" setting? Arc detection monitors high-frequency current variations that indicate a "sputtering" arc or corona discharge before a full breakdown occurs.

• Helps detect loose connections.
• Identifies marginal insulation gaps.
• Adjustable sensitivity (usually 1-9) to prevent false failures from ambient noise.

6. Why do I need to remove MOVs before testing? Metal Oxide Varistors (MOVs) are surge suppressors designed to short out voltage spikes to ground. If you apply 1500V to a 300V MOV, it will do its job and short the circuit, causing a hipot failure.

• Solution 1: Use a higher voltage MOV (if design allows).
• Solution 2: Leave MOV unpopulated until after testing.
• Solution 3: Disconnect MOV via a jumper during test.

7. How often should the hipot tester be calibrated? Industry standard dictates annual calibration (every 12 months) by an accredited lab. However, a "verification check" using a known resistor should be performed daily or at the start of every shift.

• Calibration: Yearly (traceable to NIST/National Standards).
• Verification: Daily (functional check).

8. What is the typical lead time for setting up a hipot station? If equipment is on hand, setup takes 1-2 days for programming and safety validation. If ordering a new custom fixture or automated tester, lead times can range from 4 to 8 weeks.

• Off-the-shelf tester: 1 week delivery.
• Custom fixture: 4-6 weeks.
• Programming/Validation: 1-2 days.

Glossary (Key Terms)

Term	Definition
Breakdown	Catastrophic failure of insulation where current flows freely through the material.
Class I Device	A product with a protective earth ground connection (3-prong plug).
Class II Device	A product with double insulation and no earth ground (2-prong plug).
Creepage	The shortest distance between two conductive parts along the surface of the insulation.
Dielectric	An insulating material that resists the flow of electric current.
Dwell Time	The length of time the full test voltage is applied to the DUT.
Flashover	An electric arc occurring over the surface of the insulation (air discharge).
GFI (Ground Fault Interrupt)	A safety feature on the tester that cuts power if current leaks to the operator.
Leakage Current	The small amount of current that flows through the insulation during the test.
Ramp Time	The time taken to increase voltage from 0V to the target test voltage.
Return Lead	The reference cable (usually black) connected to the chassis or ground of the DUT.
Trip Current	The maximum allowable current limit; exceeding this triggers a "Fail" result.
Type Test	A rigorous test performed on a prototype design (longer duration, higher voltage).
Routine Test	A faster test performed on 100% of production units.

Conclusion (Next Steps)

A robust hipot test procedure is non-negotiable for electrical safety compliance. It is the only way to guarantee that your product's insulation can withstand the stresses of the real world without endangering the user. By selecting the correct AC or DC parameters, setting realistic leakage limits based on data, and enforcing strict safety interlocks, you transform a regulatory burden into a reliable quality gate.

To ensure your PCB assemblies meet these rigorous standards, verify that your manufacturing partner integrates hipot testing directly into their **[PCB quality](/pcb/pcb-quality

Related links

• functional test plan pcb
• flying probe test tutorial
• quality system