What the standard pins down
IEC 60529 defines a classification for enclosures: how well the housing of a piece of electrical equipment keeps things out. The code is the letters IP followed by two characteristic numerals, optionally with further letters.
The first numeral is about solid foreign objects and about access to hazardous parts — from large objects down to dust, and from the back of a hand down to a wire. Its levels correspond to defined probes and defined test dusts.
The second numeral is about water, and each level is a different apparatus: dripping water, dripping water with the enclosure tilted, a spray within a defined angle, splashing from every direction, a jet from a nozzle of stated bore, a powerful jet, temporary immersion, continuous immersion. They are not degrees of the same test; they are eight different tests, which is why the ladder is less linear than it looks.
An X in either position means that characteristic has not been declared. That is the correct way to write an undeclared digit, and it is not a zero.
The standard also fixes how the tests are conducted and what state the equipment must be in when it is judged: an enclosure passes if the specified ingress does not occur, or does not occur in a quantity that interferes with operation or safety.
What it does not promise
It does not promise weather. Rain falls with wind behind it, at angles no spray test reproduces, for hours rather than minutes, and it brings grass clippings and pollen with it. An enclosure that passed a splash test is an enclosure that passed a splash test.
It does not promise corrosion resistance, ultraviolet resistance or freeze resistance. A code says nothing about what the housing will look like after two summers in the sun, or about a seal that has gone hard.
It does not promise the connections. On this shelf the failure is rarely the housing itself: it is the plug on a boundary wire, the joint in a drip line, the terminal in a timer that spends a winter outdoors. Those are separate from whatever the enclosure is rated.
And a code is a declaration. Where it is printed without a test behind it — which happens on the imported end of the timer and irrigation shelves — nothing in the document catches it.
The documents it sits next to
An appliance’s own product standard says which IP level it must meet, if any; this one only defines what the levels mean. A battery pack has its own standards, and a machine sold as weatherproof may also carry claims from documents about mechanical impact, which are different again.
Which shelves it reaches here
The robot mower shelf cites it most: those machines live outdoors by definition, and the code is the one piece of weather information a listing carries. So do the water timer, pump, irrigation and boundary wire families.
Where a listing quotes an IP code, this site prints both digits as given, including the X. Where a listing says “waterproof” and quotes nothing, the page prints the word in the maker’s voice and states that no code accompanies it — because on these shelves the two are not the same claim at all.
The questions that keep coming in
Can I leave an IPX4 robot mower out in the rain?
The fourth level is tested with water splashed from every direction, which is not the same apparatus as the one used for rain or for jets. Most robot makers tell you in their own manual to garage the machine, and that instruction is the answer for your machine rather than anything the code implies.
What does the X mean in IPX4?
It means the first digit — protection against solid objects and dust — has not been declared, not that it is zero. A manufacturer that has only tested the water side writes X in the place it did not test.
Is a higher second digit always better outdoors?
The levels are not a simple ladder at the top end: the test for immersion and the test for a powerful jet are different apparatus, and a product certified for one is not automatically certified for the other. Below that, higher does mean tested against more water.
Last reviewed 26 September 2026