Machinedesign 2919 12265 Js Enclosure 0

Keeping outdoor control cabinets locked up tight

Dec. 8, 2011
Several industries commonly place cabinets full of control, communication, and monitoring electronics outdoors. Telecom companies, electric utilities, as well as municipalities that need to safely manage

Authored by:
Gregory Breads
Product Manager
Dirak Inc.
Sterling, Va.
Edited by Jessica Shapiro
[email protected]
Key points:
• The latches and hinges on outdoor electronics enclosures need to withstand extreme weather and long periods without human intervention.
• Designing enclosures with durable latches, hinges, and other hardware can protect electronics for the long term.
• Hardware that is easy to install and use makes the most of the limited time and equipment available to technicians in remote locations.
Dirak Inc.
Video demonstrating snap-in hardware:
“Heading off accidental fires in solar arrays,” Machine Design, Sept. 28, 2011

Several industries commonly place cabinets full of control, communication, and monitoring electronics outdoors. Telecom companies, electric utilities, as well as municipalities that need to safely manage traffic on highways, bridges, and rail systems rely on outdoor cabinets. Additionally, wind and solar farms are now becoming major users of outdoor control cabinets.

On wind farms, electronic controllers and safety subsystems monitor the turbine, generator, tower and environment to keep the turbine operating safely and within prescribed limits. On solar farms, electronics help solar-tracking towers follow the sun.

In all these applications, outdoor electronics enclosures can be hard to reach, rarely visited by maintenance technicians and exposed to harsh weather conditions year round. The hardware must withstand high winds, storms of all kinds, heat, solar radiation, and other severe conditions that can damage electronics if they are not fully protected.

Consequently, it’s critical to specify enclosure latches and hardware that will withstand the weather, without complicating the jobs of the technicians who do visit to fix problems or upgrade equipment. Engineers should consider five factors when specifying access hardware for outdoor control cabinets: durability, ability to withstand vibration, corrosion resistance, ease of use, and ease of installation.
Long-lasting latches

Select latches that will hold access doors firmly closed and last as long as the enclosure. One option is compression latches that consistently compress gaskets surrounding enclosure openings. Compression varies from latch to latch, but one important aspect to consider is the clamping range of the latch. For instance, Dirak Inc., Sterling, Va., carries compression latches with clamping ranges as short as 3 mm to as long as 20 mm.

Fixed-compression latches have fixed cams, so they consistently compress and decompress gaskets to a specific depth. Or designers can choose latches with adjustable compression. These latches allow a user to change the initial and, consequently, the final position of the locking cam. This allows a single compression latch to be used in a variety of applications or to adjust compression on a cabinet over time.

Compressing the gasket along its entire length is important because without consistent force, gaps in the housing perimeter can let in water, dirt, or insects; any of which can damage the sensitive electronics within the enclosure.

Other hazards facing latches are vandals, thieves and even terrorists. To protect enclosures from security threats, consider whether a latch should be hand operated or locking. Locking latches can open with tools or nontraditional keys that can’t be easily forged.

Bad vibrations
Enclosures on wind farms, in particular, need to withstand vibration, an undesirable but constant side effect of wind-turbine operation. A major problem in vibration-prone enclosures is that mounting hardware can loosen and fall off over time. This can leave enclosures open to the environment or cause direct damage when nuts or bolts fall on electronics.

Sturdy access hardware that resists vibration eliminates this problem and ensures continued protection. Look for antivibration latches and other access hardware that reduce rattle and noise.

There are several types of antivibration hardware to consider. Some keep various parts of the enclosure under a constant force that helps prevent loose parts from rattling against each other. The compression latches mentioned above fall into this category.

Other antivibration hardware uses snap-in designs in which wedges or other design features snap into place and hold the hardware in constant compression. One example is Dirak’s Snap-Line products, which don’t require nuts, bolts, or washers that could rattle loose. Another strategy is to include elastomeric components on latches that can absorb vibrations.

Designers concerned about vibrations should test hardware to be sure it can withstand the vibration environment expected in the field. Another option is to choose products whose ability to withstand the expected vibrations has been certified by a third-party laboratory.

Corralling corrosion
Outdoor enclosures are constantly exposed to ice, rain, sunlight, salt, animals, high winds and other harsh conditions. Using corrosion-resistant latches and hinges extends enclosure life and helps cut down on maintenance visits.

Choosing corrosion-resistant hardware is mainly a matter of material selection. Stainless steels resist corrosion, as do plastics.

However, designers should check the properties of the chosen material to be sure hardware items have the desired strength, rigidity and look while ensuring the material can meet both the required fatigue and environmental requirements to ensure that they will last the life of the enclosure.

Form and function
Latches, fasteners, and hinges need to combine function and design. Even though they are small parts of the enclosure, their aesthetics and ergonomics should support or enhance the enclosure’s style and function. Function is especially important for enclosures on wind and solar installations because once a technician leaves a site, the equipment is generally unmonitored for extended periods.

One latch feature that aids maintenance workers is “locked” and “unlocked” indicators. Another beneficial feature is push-to-close or slam latches that eliminate secondary steps needed to secure the enclosure.

Periodic maintenance and electronics upgrades mean enclosure-access hardware needs to operate easily in the field. And in the case of a major retrofit, the hardware should make it easy to remove the enclosure door entirely. Specifying lift-off hinges is one way to ensure the technician can have easy, unobstructed access to the inside of the cabinet.

The best latches offer clear, simple designs and a low profile, ideally even flush or recessed options. Flush or recessed mounting eliminates snag points in vertical installations and tripping hazards in horizontal, floor or roof-mounted ones. Concealed lift-off hinges contribute to an enclosure’s security, appearance, and ease of use.

Initial installation
In addition to making maintenance and upgrades easier, enclosure hardware can be designed for ease of installation. Snap-in designs (see sidebar) offer secure mounting and significantly quicker installations. They lower inventory requirements because they don’t need installation tools such as screws, nuts, bolts, or washers.

Snap-in hardware is quick and easy to install. Technicians can install a piece of snap-in hardware in as little as 10 to 20% of the time needed to secure a hinge or latch that needs traditional fasteners like nuts and bolts.

Hardware that snaps in also permits blind installation; ideal when reaching the back of an enclosure panel is difficult or impossible. The hardware also withstands vibration and permits easy disassembly for maintenance, repair or end-of-life recycling.

It’s a snap

Dirak’s Snap-Line products use D-Snap technology to install latches, hinges, handles and fasteners into sheet-metal panels.

Each piece of hardware has wedge-shaped, spring-loaded wings that retract when manually inserted into precut holes in the panel. Once the hardware is fully inserted, the wings snap into position.

D-Snap hardware attaches without mounting tools such as screws, nuts, bolts, and washers, or welding. By eliminating mounting hardware, companies can cut part count and inventory requirements, technicians need to carry fewer tools into the field, and hardware can be installed securely from the front if access to the back of the panel is limited.

Snap-Line products withstand vibration and are rated for heavy loads. Because they don’t rely on mated threads to maintain a tight fit, they stay secure in the panel over time.

The hardware can be removed easily when the enclosure needs to be disassembled for upgrades, maintenance, or end-of-life recycling. A special tool retracts the wings and lets users pull the hardware out of the panel. There’s no need for heat guns or solvents that often must be used to loosen thread-locked fasteners.

© 2011 Penton Media, Inc.

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