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IP20, IP65 or IP66 — what do those numbers mean?

The protection rating decides whether a device may sit outdoors or must stay inside.

Technical · 09/10/2026 · 2 min read

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Every inverter and storage battery carries a line such as IP20, IP65 or IP66. Most people skip past it, but that number decides where the device may be installed. Understanding IP65 and IP66 protection ratings avoids one very expensive mistake: putting an indoor device outside.

What those two digits mean

IP stands for Ingress Protection — protection against things getting in. Two digits always follow:

  • The first digit — protection against solids, 0 to 6. Six means fully sealed; not even dust gets in.
  • The second digit — protection against water, 0 to 9. The higher the number, the heavier the water it withstands.

The three ratings you will meet

IP20 — protected against solids larger than 12.5 mm, meaning a finger cannot reach live parts. But the second digit is zero: no water protection at all. An IP20 device must stay indoors, in a plant room or a dry electrical cabinet.

IP65 — fully dust-tight and able to withstand water jets from any direction. Suitable outdoors, and fine in rain.

IP66 — also fully dust-tight, but rated against considerably more powerful water jets than IP65. In practice this is the rating you normally see on wall-mounted outdoor inverters.

Which rating for which location

  • Plant room, under the stairs, anywhere dry indoors — IP20 is enough, and usually cheaper.
  • A covered walkway where rain still blows in, a balcony, a roofed terrace — IP65 or above.
  • Mounted on an outside wall, exposed to sun and rain — IP66.

In the current catalogue most inverters are IP66, with a few single-phase hybrid models available as IP21 or IP65. Storage batteries come in both versions: IP20 for indoor installation and IP65 for outdoors. Panels are rated IP68 because they sit on the roof all year.

A high rating does not mean install it anywhere

IP66 handles water well but says nothing about temperature. An inverter in direct midday sun still heats up and throttles its own output to protect its components — losing you production at exactly the sunniest moment. So even an IP66 unit should be mounted in shade or given a small canopy.

One more thing: an IP rating only holds while the enclosure is intact. Drilling extra holes in the case, leaving a gasket unseated, or running cables incorrectly through the gland all void the rating printed on the label.

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