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Keep Electronic Projects Secure and Weatherproof for the Long Haul with the Right Enclosures

By Patrick Mannion

Contributed By Digi-Key's North American Editors

For many designers of DIY or prototype projects, once the electronics are laid out, finding a suitable enclosure is often left to the last minute. This may be reasonable if it’s going to be used indoors on a desk or placed on a wall, temporarily. But if the project is intended for use outdoors over a long period of time it will quickly succumb to the elements or be damaged, either intentionally or unintentionally by malicious tampering or idle curiosity. 

It’s difficult to craft an appropriate enclosure using available materials, and while off-the-shelf enclosures might meet ruggedness requirements, they may not be the right size, are overly vulnerable to tampering, and lack aesthetics. The latter two can be problematic if it’s going to on the outside of a home or commercial building.

For small electronic project housings or enclosures that will be placed outside, it’s best to opt for a line of officially IP-68 qualified polycarbonate enclosures that can seal the electronics effectively against the elements.

This article will discuss the effects of rain, temperature extremes, and sunlight on electronics systems and their enclosures. It will then describe what IP-68 protection implies before introducing enclosures from Hammond Manufacturing with associated gaskets that meet both physical and aesthetic requirements.

Why electronics enclosures need to provide environmental protection

Electronic systems used outdoors are susceptible to deterioration due to heat, cold, humidity, direct sunlight—particularly ultraviolet (UV) rays—vibration, and physical tampering. They are also subjected to many sources of electrical and electromagnetic noise. Designers can account for temperature extremes through proper circuit design, component derating, and thermal management techniques such as heatsinks, fans, and by minimizing overall power consumption. Vibration can be accounted for by mounting pc boards on vibration isolators, and electrical and RF noise can be mitigated using filters, chokes, and appropriate grounding techniques.

However, moisture and humidity are particularly pernicious. Once moisture has penetrated a system it can increase humidity, lead to condensation, followed by corrosion and ultimate deterioration over time of semiconductor passivation layers, solder joints, and physical connections. When combined with contaminants such as dust and debris that may have entered the enclosure before it is closed, the detrimental effects are multiplied. The various ways in which moisture affects components include electrochemical, galvanic, anodic, and cathodic. All pose a hazard to the reliability of electronics, some subtle, some more obvious (Figure 1).

Image of effects of moisture and humidity on electronic componentsFigure 1: The effects of moisture and humidity on electronic components, boards, and interconnects can be highly detrimental over time. (Image source: PCFixit.au)

The effects of moisture ingress can be mitigated through techniques such as placing epoxy or gels over critical components. For mass-produced systems, conformal coatings of 20 to 50 microns, or even up to 100 microns in extreme cases, can cover the entire pc board and be a good solution. However, some components, such as DIP switches, variable resistors, and battery holders can’t receive such coatings. Also, conformal coatings may not quite cover the edges (edge crawling), exposing traces and connections to corrosion.

The full effect of moisture depends upon heat and relative humidity. Full testing guidelines for moisture and humidity for outdoor equipment is covered by ETSI EN 300 019-1-4 V2.2.1 (2014-04) “Environmental Engineering (EE); Environmental conditions and environmental tests for telecommunications equipment; Part 1-4: Classification of environmental conditions; Stationary use at non-weatherprotected locations”.

This is a useful testing guide for hobbyists, and essential for professionals. It classifies the various conditions a device might face into seismic, earthquake, shock, solar radiation and temperature. It further sub-divides environmental classes into water, precipitation, mold growth, animal attacks (i.e., termites), and air salinity. It also has some good definitions that are directly relevant here and underscore the importance of humidity:

  • Absolute humidity: Mass of water vapor in grams which is associated with one cubic meter of dry air in an air/water vapor mixture.
  • Non-weatherprotected location: Location at which the equipment is not protected from direct weather influences.
  • Relative humidity: Ratio of the partial pressure of the water vapor in moist air at a given temperature, to the partial pressure of the water vapor in saturated air at the same temperature.
  • Stationary use: Use of the equipment mounted firmly on the structure, or on mounting devices, or it is permanently placed at a certain site.

For designers, however, prevention is always better than a cure. This is where the International Protection (IP) rating IP-68 comes into play.

What is IP-68?

Also called ingress protection, the IP codes derive from EN 60529 and assign two digits that indicate the degree of protection provided with respect to dust and moisture (Figure 2). The assignments classify the degree of protection provided against intrusion of solid objects, such as fingers and hands, as well as dust and water. The goal is to provide clarity around otherwise vague and subjective terms such as “waterproof”.

The first digit after IP pertains to solids, the second digit pertains to liquids. So, in the case of IP-68, a system is compliant if it’s totally protected against dust (6) and long periods under water jets or immersion under pressure (8). 

Table of IP codes assign a digit to indicate a system’s degree of protectionFigure 2: The IP codes assign a digit to indicate a system’s degree of protection against dirt (left) and moisture (right). (Image source: focusondrives.com)

How to meet IP-68 requirements

While it’s possible to design an IP-68 enclosure from scratch, there’s really no need to re-invent the wheel when companies like Hammond Manufacturing have already done the groundwork. Its 1557 Series of enclosures for harsh environments are designed with UV-stabilized polycarbonate material to meet IP-68 requirements, while also attending to aesthetics, providing a “modern” look with “soft” curves in two colors—black and light gray (Figure 3).

Image of Hammond Manufacturing 1557 Series of enclosuresFigure 3: The 1557 Series of enclosures accommodate both IP-68 requirements and design aesthetics, while providing a variety of mounting options. (Image source: Hammond Manufacturing)

The 1557 Series carry a flammability rating of UL94-5VA and achieve protection against dust, oil and water ingress by using a two-piece tongue-and-groove construction with a high-temperature, UL listed silicone gasket, model 1557BGASKET (Figure 4).

Image of Hammond Manufacturing 1557BGASKET is made of UL listed siliconeFigure 4: The 1557BGASKET is made of UL listed silicone and helps the 1557 enclosure achieve IP-68 compliance. (Image source: Hammond Manufacturing)

The lid is then secured with M4 stainless steel machine screws, model SC576-50 (Figure 5). These are threaded into corrosion-resistant bushings to allow for repetitive assembly and disassembly, such as during the prototyping stage of a design.

Image of Hammond Manufacturing model SC576-50 M4 machine screws Figure 5: The model SC576-50 M4 machine screws thread securely into corrosion-resistant bushings to allow for repetitive assembly and disassembly. (Image source: Hammond Manufacturing)

The 1557 Series comes in a wide range of sizes to meet a variety of application needs, and comes with a range of mounting options–including pc board—for placement flexibility. The sizes are based on four basic plan sizes, each in two heights. The sizes are:

  • 80 x 80 mm floor plan, in heights of 45 millimeters (mm) or 60 mm
  • 120 x 120 mm, 160 x 160 mm, and 200 x 200 mm floor plans, in heights of 45 mm or 70 mm

The mounting options are as shown (Figure 3, again):

  • Heavy-duty, wall flange mount (mounting feet outward)
  • Flush wall mount (mounting feet as keyhole slots)
  • Desktop/tabletop (rubber feet included)

Each option has a clear emphasis. The heavy-duty wall-mount model has a set of two or four wall-mounting tabs which are securely screwed to the back of the enclosure. The tabs protrude out from the edge of the enclosure, allowing the user to securely mount it to the wall using their own hardware. This is ideal for applications where security is critical and the installation is permanent.

The flush-mount model has the same wall-mounting tabs, but they are flipped around and installed into cavities on the back of the enclosure. In this configuration, the tabs act as keyhole slots, allowing for a more elegant, flush-mount appearance. This configuration is also ideal for applications where the enclosure will be temporarily affixed to the wall.

Each enclosure includes four adhesive rubber feet for use in desktop/tabletop mode. In this mode, the wall-mount tabs are no longer used, and rubber feet are placed in each corner. There is a recessed area in each corner sized for the feet to ensure proper placement, maintain a lower profile, and to keep the feet securely in place. More rubber feet, model 1421T6CL, can be ordered if necessary.

Accessories that come with the enclosures include liquid-tight cord grips/cable glands and pole-mount kits.

Conclusion

Much development work is focused on the design of the electronics, to the extent that designers can underestimate how important it can be to choose the right enclosure for outdoor applications. Without suitable protection, humidity, temperature extremes, dust, oil and other contaminants can combine to compromise the electrical and structural integrity of a design.

However, such enclosures are difficult to design. By choosing off-the-shelf enclosures that meet IP-68 requirements, designers can quickly get a design to market that will meet the challenges of extended outdoor use.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Patrick Mannion

After starting in engineering, Patrick Mannion has been analyzing the electronics industry for over 25 years, with a focus on informed editorial to help engineers manage risk, contain costs, and optimize designs. Formerly brand director and vice president of UBM Tech's electronics group, he now provides custom content services.

About this publisher

Digi-Key's North American Editors