Water Temperature in IP Testing: An Overlooked Variable

IEC 60529 does not fix the water temperature for most tests, which means two laboratories can run the same test at 10 degrees and 25 degrees and get different results.

The physics

When a warm enclosure is sprayed with cold water, the air inside contracts and a partial vacuum forms, drawing water through paths that would otherwise stay dry. The effect is strongest in sealed enclosures with a large air volume, and it is exactly the condition a product sees when it is left in the sun and then rained on or washed.

What to specify

State the water temperature in the test report, and where the product standard allows it, test with the sample at its maximum operating temperature and the water at the low end of the ambient range. That is the worst credible case.

Condensation afterwards

After a cold water test, water condensing on the inside of a warm enclosure can be mistaken for ingress. Allow the sample to equalise at room temperature before opening, and distinguish droplets on cold surfaces from pooled water at the bottom.

Related technical notes

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• Specifying an Outdoor Cabinet: IP Rating Plus Everything Else
• Simulating Rain: When IPX3 or IPX4 Is the Right Model