When designing a piece of hardware that has even the faintest chance of being exposed to the elements, it’s best to repeat this mantra: water finds a way. No matter how much you try to shield a project from rain, splashing, or even just humid air, if you haven’t taken precautions to seal your enclosure, I’ll bet you find evidence of water when you open it up. Water always wins, and while that might not be a death knell for your project, it’s probably not going to help. And water isn’t the only problem that outdoor or rough-service installations face. Particle intrusion can be a real killer too, especially in an environment where dust can be conductive.
There’s plenty you can do to prevent uninvited liquid or particulate guests to your outdoor party, but it tends to be easier to prevent the problem at design time than to fix it after the hardware is fielded. So to help you with your design, here’s a quick rundown of some standards for protection of enclosures from unwanted ingress.
The Other Kind of IP
Why have a standard for enclosure ratings in the first place? Easy — so engineers know what they’re buying. Before international standards for protection, any manufacturer could slap a label on device claiming it was “waterproof” or “dustproof” and get away with it. The International Protection Marking standard, or IP Code, was developed to provide a more objective measurement of how well the stuff inside an enclosure is protected from solids and liquids.
The IP Code has two ratings, each represented by a single numeral, with larger numbers reflecting higher degrees of protection. The first character of the IP Code is for particles, and the second is for liquids. If either test was not performed, an X is substituted for the number. So, “IP54” and “IPX7” are valid IP codes, while “IP6” is not.
Particle ingress ratings range from 0 (offering no protection) to 6 (dust proof). IP1X basically prevents you from sticking your whole hand into a circuit panel, IP2X prevent you from getting a finger anywhere nasty, and IP3X and IP4X protect against tool intrusions. IP5X and IP6X address degrees of dust protection. IP particle ratings are cumulative, so that an IP6X enclosure protects against everything from dust to screwdrivers to human hands.
On the liquid side, things are a little different. Ratings again start at 0 (no protection) and run through 6 (protection from direct high-pressure jets of water), and again ratings up to IPX6 are cumulative. IPX7 specifies protection from submersion for 30 minutes at 1 meter, but does not guarantee any of the previous ratings — as you can imagine, a cell phone rated for a couple of seconds in a toilet might not fare well against a pressure washer. If a device is tested for two liquid standards, you’ll see something like “IPX6/IPX7,” meaning you can really go to town on it at the car wash. IPX8 also specifies immersion, but leaves the manufacturer in charge of defining how deep and for how long.
The last liquid rating is IPX9K, which is basically the steam cleaning standard for washdown scenarios. It specifies high-pressure, high-temperature protection. The video below shows some pretty gnarly tests on a switch — note that IP ratings apply to any kind of enclosure, not just the box you build a project in. It wouldn’t do to use an IPX9K enclosure only to put an IPX0 switch on the case.
What about NEMA?
In the USA we have another set of standards that address ingress by objects and liquids. The National Electrical Manufacturers Association (NEMA) defines a set of standards for enclosure specifications. Unsurprisingly known as the NEMA ratings, the standards are a little more subjective than the IP ratings, specifying things like “windblown dust” and “light spray.” The categories are more situational, like NEMA 5, which is an enclosure “provided with gaskets or equivalent to exclude dust; used in steel mills and cement plants.” NEMA ratings are intended mainly for industrial enclosures; thus, while IP68 cell phones are becoming a thing, it’s not likely we’ll ever see those phones rated at the approximate equivalent NEMA 6P.
And while there are some general alignments between IP Codes and NEMA types for enclosures, the two standards are means to different ends. NEMA ratings cover a lot of other aspects of industrial enclosures, like corrosion resistance, protection against oil versus aqueous liquids, explosion proofing, suitability for hazardous locations, and the like. So if you’re just worried about water creeping in, some NEMA ratings may be overkill, but if you’re looking for something that won’t rust, they may be just what you’re looking for.