The DC high voltage test—also known as DC Hipot (high potential test)

What exactly is a DC Hipot?

A hipot is a dielectric strength test: you deliberately stress the insulation of a DUT (device under test) “above normal.” If the leakage current remains within limit and no breakdown occurs, the insulation is sufficiently robust. In the DC variant the voltage is direct current; after the initial charging current you mainly see the pure leakage current (the reactive component drops out), which often makes the insulation’s behavior easier to judge.

When do you choose DC instead of AC?

• High capacitances in the product (long cables, filters): DC prevents continuous capacitive charging currents as with AC, which makes the measurement more stable. You must, however, actively discharge afterwards.
• Accurate leakage-current analysis: DC primarily measures the true leakage current without the charge and discharge currents of the capacitive part; AC also measures reactive components.

How a DC Hipot works step by step

1. Set up and interlock safely the test arrangement (test cage/safety fence, interlocks, emergency stop). Guidelines: EN 50191 for safe electrical test installations.
2. Connect the DUT and check correct polarity and distance to grounded parts.
3. Define ramp time (ramp profile) for the test voltage (e.g., x V/s) to avoid unwanted inrush spikes (current).
4. Test time (hold voltage, typically 1–60 s depending on standard/process) and monitor leakage current.
5. Trip criteria: exceeding leakage current limit or breakdown = FAIL; otherwise PASS.
6. Actively discharge the DUT on DC before disconnecting or touching anything.

Typical applications of DC Hipot

• Cables, motors, coils, transformers, sensor and actuator leads
• Power supplies and modules with high input/output isolation
• Quality control of HV components
• Assemblies with longer clearance and creepage distances In all these cases you want rapid detection of insulation faults, contamination, mechanical damage or production defects (adhesive, resin, clearances).

DC vs. AC: the key differences

Standards and safety: what must be in place?

• EN 50191 is the reference for safe test workstations/installations: guarding, interlocks, distances, procedures, training. A risk assessment and appropriate organizational measures are mandatory.
• Operator safety: never touch the DUT during the test, use appropriate guarding and ensure active discharge after DC tests.
• No discharge after a DC test → always actively discharge before disconnecting.
• Ramp too aggressive → set an appropriate ramp rate to avoid false trips from charging currents.
• No interlocking/guarding → make the workstation EN 50191-compliant, including interlocks and emergency stop.

“Hot hipot” during functional testing: when is it useful?

Sometimes you deliberately apply high voltage while in operation (relays/coils energized) to involve all circuits—for example with complex assemblies. This increases the chance of finding fault paths that “cold testing” can miss. Determine per product whether hot hipot adds value and tighten safety accordingly.

• Multifunctional stations (hipot + PE + ISO + leakage current) with automatic switching of test methods
• Mobile test setups: IONIO has various mobile setups up to 80 kV DC
• Test flow & data: ramp/hold profiles, thresholds, trip logic and full traceability with measurement data logging.
• Training & service: we train your team and provide service and calibration—so your test environment remains demonstrably compliant and reproducible.

Conclusion

DC hipot is the right measurement for determining insulation quality, especially for products with high capacitance and windings. Combine it with a safe workstation, well-designed ramps/steps and solid data—this prevents field failures and accelerates release. Want to get this right in one go? We design, supply and implement the complete solution around your product and standards. Contact IONIO for a no-obligation consultation.