Outdoors, or in wet indoor environments like wash-down areas, Low Humidity Control Cabinets of electronic systems begin with the design of the enclosures and penetrations, and end with the design and configuration of the components. This short article concentrates on several of these best practices.
Assume your enclosure will leak. Unless the application form requires a vented enclosure (e.g., for heat dissipation, battery off-gassing), a sealed enclosure represents the first line of defense against moisture. Unfortunately, even the best NEMA 4 electrical enclosure works great until poor installation practices or out-year modifications create poorly sealed penetrations (Fig. 1).
It’s better to think that penetrations into any enclosure are going to leak (as shown by Fig. 2). Based upon this assumption, top-mounted conduit penetrations where moisture can collect on horizontal surfaces should be avoided. Even if Myers hubs or sealing locknuts are employed for code compliance, enclosure penetrations should be made below energized parts, whenever possible.
With regards to cable penetrations (versus conduit penetrations), directing water out of the electrical enclosure or housing with the use of drip loops (Fig. 3) is yet another best practice. The next step is to heat-shrink the connector fittings and alternate wrappings of electrical tape and butyl self-adhesive rubber tape to safeguard against moisture intrusion into the connector.
Maintaining door seals is incredibly important. Door seals should be inspected to make certain panel doors are sealing properly by observing surface wear on the seals. Larger doors with few latches are particularly problematic as flexing in the door may prevent a uniform seal. And lastly, seals needs to be inspected for pinching, tears and proper adhesion to original mating surfaces.
Assume all conduits contain moisture
The next best practice for Dry Cabinets For PCB Storage of electronics assumes that even when the conduit penetrations are perfectly sealed, the conduits are still planning to contain moisture. Underground conduit often is left unsealed during construction (allowing moisture accumulation), and conduit runs can potentially have multiple points where moisture can enter. Conduit with Desiccant Dry Cabinets can transfer water vapor in to a sealed enclosure. Typically, when electronics are energized, heat is generated and the air within the enclosure can hold even more moisture than ambient conditions, meaning water vapor is a smaller problem. The problem takes place when the enclosure temperature drops (as a result of equipment being de-energized, cooler nighttime temperatures, cooler weather conditions, etc.) as well as the temperature inside xakleh enclosure drops beneath the dew point, resulting in condensation.
Expanding polyurethane foam sealant (Fig. 4) offers an excellent approach to sealing around conduit cabling: It’s been found to get superior to silicone, primarily because caulking guns combined with silicone are hard to insert far enough to the conduit to attain an effective seal. An expanding foam nozzle attachment can be inserted further into the conduit to produce a powerful seal around the cabling.