What is "Hi-Pot" Testing

(Last edited 8/17/2026)

This book continues to expand as new needs emerge. I had considered adding a dedicated section on safety certifications... what they signify, how they're obtained, and the testing required. It seems that section can't wait. Already this month, and we're only midway through, I've twice been asked whether Hi-Pot testing could be taken out of S.O.P. One instance involved reworked units addressing design flaws; the other, assemblies from knockdown kits. In both cases, the answer was unequivocally no.

For hobbyists that are aware of the risks performing personal repairs, Hi-Pot may seem unnecessary. And, despite what your average Reddit user says, if you service equipment on a regular basis for others, and someone is electrocuted using a unit you last handled, you might face consequences no one should risk.

Hi-Pot (High Potential), or dielectric withstand testing, verifies the insulation between hazardous live parts and accessible surfaces remains effective. For example: applying 1800 VAC or 2546 VDC between primary circuits (AC Line or Neutral) and Earth Ground, with leakage current kept below 5 mA for a specified duration is a "pass".

What the test is actually doing:

Think of a PSU's safety isolation barrier:

• a Hi-Pot test between the primary side (AC Line and Neutral) and Earth Ground, with test levels such as 1800 VAC or 2546 VDC, leakage trip current below 5 mA, and a specified test duration.
• Secondary side: +12V, +5V, +3.3V outputs
• Chassis and protective earth

A Hi-Pot test subjects the insulation barrier to a voltage significantly exceeding the unit’s normal operating levels (e.g. 1800 VAC), while precisely monitoring any leakage current (e.g. 5 mA). A failure occurs if the insulation breaks down, allows arcing, or permits current leakage beyond acceptable limits. This test answers a critical safety question: under surge or fault conditions, will the isolation barrier continue to protect a user from mains voltage?

Why it is critical after rework or reassembly?

Every time a PSU is disassembled and reassembled, you create opportunities to damage the insulation system.

Typical failure mechanisms include:

1. Pinched wires

   A wire can become trapped between:

   • PCB and the chassis
   • PCB and heatsink
   • Chassis panels or even Mylar panels
   • Parts of the fan

   The insulation may look fine from the outside but can have internal damage.

2. Missing insulation materials

   During reassembly it is easy to forget:

   • Mylar sheets
   • Pieces of tape
   • Nuts, bolts or washers
   • Isolation barriers

   Many of these parts can be safety-critical rather than functional.

3. Hardware mistakes

   A screw that is:

   • Too long
   • Installed in the wrong location
   • Missing an insulating washer

   This can reduce creepage/clearance distances or directly contact a conductor.

4. Damaged transformer isolation

   If a transformer or inductor is removed and reinstalled, mechanical stress can damage insulation between the primary and secondary windings.

5. Solder and debris

   Rework can leave:

   • Solder balls
   • Cut wire strands
   • Metal shavings
   • Excess flux contamination

These may create partial conductive paths that only reveal themselves under high voltage stress. Hi-Pot testing is specifically good at finding manufacturing and assembly defects such as insulation damage, contamination, inadequate spacing, or stray conductor strands.

Why continuity testing is not enough

Just like when you try to use a DMM to measure the resistance of a wire without a load on it; a DMM continuity check only tests at a few volts.

A defect might pass:

• Continuity
• Functional testing
• Burn-in
• ATE

...and still fail when several thousand volts are applied.

For instance:

A Mylar sheet that's been slightly damaged might hold up just fine under the normal 400 VDC found across the bulk capacitor. However, subject it to an 1800 VAC Hi-Pot test, and it could instantly flash over. This is precisely the sort of hidden flaw the Hi-Pot test is designed to uncover.

In terms of safety, the Hi-Pot test serves as the definitive check that a finished product is safe for use.

To put it plainly: in any professional context, be it with engineering samples, qualification units, RMAs, or lab rework, if you've opened the power supply and done internal work that might impact insulation, clearances, wiring, shielding, barriers, transformers, heatsinks, screws, or wire routing, performing a Hi-Pot testing isn't just recommended; it's essential. Skipping this post-rework verification means you cannot confirm the integrity of the safety isolation system.