Humidity Preconditioning: The Step That Decides the Dielectric Result

Dielectric strength and insulation resistance are strongly dependent on moisture. The standard therefore requires the equipment to be conditioned in a humid environment before those tests, so that the result represents the worst condition the equipment is rated for rather than a laboratory best case.

What the conditioning does

Moisture is absorbed into hygroscopic materials and films onto surfaces, reducing surface resistivity and increasing leakage. A moulding that is a good insulator when dry can become a tracking path when wet, especially if it has contamination from handling or from manufacturing residues such as flux.

Why equipment fails after conditioning

Flux residue that was never cleaned, which becomes conductive when moist. A gap that is adequate in air but bridged by a water film across a contaminated surface. A sealed enclosure that was assumed to be sealed but admits moisture through a cable gland or a gasket that is compressed beyond recovery. All three pass dry and fail wet, which is why a dry-only test is not evidence.

Doing it consistently

Condition for the specified time at the specified temperature and humidity, in a chamber that actually reaches those conditions at the surface of the sample, then test promptly, because the moisture starts to redistribute as soon as the sample leaves the chamber. Record the conditioning parameters; a report that omits them cannot be compared with another report.

Related technical notes

• IEC 61010 and IEC 62368-1: Which Standard Applies to Your Bench Instrument
• The Ten Findings That Repeat in IEC 61010 Testing
• Preparing a Sample for IEC 61010 Testing