This Way to the Ingress: Keeping Stuff Dry and Clean with IP and NEMA

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.

Click to embiggen

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.

[Featured images from Holland Shielding BV and AutomationWorld]

25 thoughts on “This Way to the Ingress: Keeping Stuff Dry and Clean with IP and NEMA

  1. It might seem intuitive but unless you have spent time sourcing it, it might not be readily apparent. Therefore, it is important to note that generally protection ratings scale fairly linearly in terms of greater protection as you move up tiers towards more resistance. Makes sense, higher ratings protect against more extreme conditions. But what might not be clear is that the cost of greater protected items traditionally does not scale anywhere close to linearly. Especially at the pressure rated or directed stream end of things. Also, the variety and number of offerings that meet the high end of that scale also drops dramatically.

    Still, the industry as a whole seems to at least be aware that there very much is a market for basic water resistance as a standard offering and even consumer products THAT COMMONLY ENCOUNTER THE ELEMENTS (looking at you cell phones) are starting to build this in as well. It’s just difficult to do unless you design it from the ground up and actually are able to source interfacing components rated for that as well.

  2. What always amazes me is the role atmospheric humidity plays in filling enclosures with water. If the tiniest vent exists, the cabinet sucks in air during times of high pressure, and expels air when the outside is at low pressure. This “breathing” brings in air at whatever the current humidity level is. Later, when the temperature inside of the box drops to the dewpoint, the moisture condenses inside the box; as it warms up, it drains to the bottom and pools there. The next exhalation cycle expels air before the liquid inside has evaporated, and the next inhalation can bring in more humid air. Rinse and repeat.

    I can hang a perfectly dry box outside, and seal it as good as I possibly can. But when I check on it at the end of a season, it’s still got a puddle of water in the bottom, because I managed to seal the bottom against water leaving. The fix seems to be to keep a drain/ventilation hole open in the bottom of the box. That also manages to keep the spiders happy (because I never remember to put a band-aid over the drain hole.)

    1. Humidity can enter the enclosure inside cables (from the far end of the cable), even if the cable entry point is well sealed). Though airflow inside cables may be slow, pressure differences can make it “breathe” slowly over time, bringing moisture to condense inside the enclosure. Dessicants only work until saturated.

    2. This is why when designing for water and dust resistance you actually design to make something _not_ airtight, instead you control where the air can enter. At that point you use a special membrane or vent assembly to let the air pressure equalize, but not let in dust or moisture (ideally you also want moisture to be able to escape though). There are different options out there, but Gore probably has the most market-share

    3. Try this, have two boxes, one out aluminium one that has a bottom drain, then an inner plastic one that has a block of calcium sulphate at the bottom. Most of the moisture condenses in the outer box and drains away, the rest is absorbed by the calcium sulphate and released slowly when the ambient conditions reverse.

      Now if only I could find a, low power, solution to the problems that fog causes with 2.4GHz radio transmissions…

    4. Had that problem with one of the headlights on my 1998 Taurus. As long as there was any moisture inside the housing, it’d draw in more until it was sloshing around. The vent on top was as it should be, not clogged.

      To stop it I had to slosh some 91% rubbing alcohol around inside the housing then put it in a dehydrator until it was totally dry inside. Since reinstalling it on the car it’s stayed dry.

      I’d tried taking it off the car, removing the bulb and setting it out in direct sunlight all day. It seemed to be dry but a couple of days later I could’ve used it for a goldfish bowl.

  3. An old ham radio adage was to make an outdoor enclosure as airtight as possible, so water cannot possibly get into it, and then drill drain holes in the bottom to let the water out.

    One often neglected source of water ingress is inside cables or wires, between the metal and insulation (or between wires). Differences in air pressure can cause significant (over time) airflow inside these cables, and that airflow can contain humidity. Both ends of every cable must be in a hermetically sealed environment.

    1. It is a good idea to use outdoor rated grease-filled cables.
      They actually work very well to keep water out of enclosures by letting the grease melt in the summer and fill your enclosure. No room for water means no water.
      I have install photos somewhere of a cable jacket sliced open and folded into a drip loop inside a pop bottle; kept the grease contained, and let us know when it needed to be replaced because the water in the cable floated above the grease in the “inspection bottle.”
      Thankfully, we have evolved this technology to fill the cables with a temperature-stable grease. All of the benefits, and less of the problems.

      This is also a good topic for a future Hackaday article.
      The millions of kinds of wire, and where to use them.

  4. There were some real shit articles on Hack A Day recently, however this is a topic that could use a lot more coverage. It’s relevant to makers and professionals.

    Outdoor enclosures with field wiring are not simple to design as water is very difficult to stop.

    Sort of like buying a house, your #1 enemy becomes water leaks or blockages.

  5. as mentioned already, drip holes can be a very important part of a rain tight enclosure. When it comes to electrical, it’s actually a requirement of the nec to ensure proper drainage of outdoor boxes and conduit fittings where water may gather.

    Another interesting area to explore along this same thread is how explosion proof equipment works. When dealing with electrical equipment people figured out very early on that it was unrealistic in most applications to keep all explosive vapors out of electrical boxes; therefore they design them backwards to how many think. They are actually designed on the assumption that flammable gas will enter them, and then they contain explosions and allow the gas to vacate the enclosure such that it doesn’t become a bomb and that by the time the gasses trying to escape reach outside the box they are cool enough to not ignite the flammable vapors in the vicinity.
    That’s super cool! imho

    1. ExD equipment is pretty impressive, especially the intimidating price and the specificity of the installation- even the washers for the cover form part of the flame path and cant be removed or altered. All cables however are sealed with an ExD compression gland and epoxy where terminated to stop the explosion traveling. The whole Hazardous Area equipment rating and compliance is pretty laberenthine.

    1. SiliconE oil is pretty expensive compared to mineral oil.
      It’s cheaper to design a pump with no dead space for water to fill than to fill it all with oil. Other than that multiple o-rings are the usual solution. Potting electronics, using magnetic couplings, diaphragms, or pneumatic bladders are other solutions.

      1. The only high end submersible pumps I’m aware of are those installed in oil wells. The factory serviceman fill them with an oil when ran into the well, the nature of the oil I don’t know. Where in many instates there are several thousands of salt water above the pump, water that’s heavier than the planet’s surface oceans. For that reason I don’t think the oil has nothing to do with water ingress because the servicemen never pressurized it so it could stand up to the static pressure in the well bore. They simply pumped the oil into a lower port until it flowe out a higher port and the ports where closed. I’m sure the heat from the motor pressurised thee oil to a degree, but I doubt it was enough to fight ingress. My thinking the oil job is to transfer heat from the motor windings to the case. Many of those pumps are of many multiples of HP in a very compact enclosure. Where I have never seen every possible installtion, there’s that chance I could be mistaken

  6. The gold standard in the automotive industry, dealing with 12-year warranted design-life requirements, and thorough design validation testing, the most common requirement for automotive power electronics being IP6K9K (reinforced protection against pressure washers etc):

    Use a membrane vent.

    The enclosures are designed as airtight as possible, but instead of actually drilling a ventilation hole in the bottom, which is not an option for harsh automotive conditions, the time-tested answer to these problems is the use of an “expanded PTFE” membrante vent.

    This FAQ tells it all: (Warning, link goes to a commercial supplier):
    https://www.gore.com/resources/faq-for-gore-protective-vents

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s