Outdoors, or in wet indoor environments like wash-down areas, Dry Storage Cabinets of electronic systems begin with the appearance of the enclosures and penetrations, and end with the design and configuration of the components. This post focuses on several of these best practices.
Assume your enclosure will leak. Unless the application form calls for a vented enclosure (e.g., for heat dissipation, battery off-gassing), a sealed enclosure represents the very first line of defense against moisture. Unfortunately, even the best NEMA 4 electrical enclosure is effective until poor installation practices or out-year modifications create poorly sealed penetrations (Fig. 1).
It’s better to think that penetrations into any enclosure will leak (as shown by Fig. 2). Based upon this assumption, top-mounted conduit penetrations where moisture can collect on horizontal surfaces ought to be avoided. Even if Myers hubs or sealing locknuts are used for code compliance, enclosure penetrations ought to be made below energized parts, whenever possible.
When it comes to cable penetrations (versus conduit penetrations), directing water away from the electrical enclosure or housing through the use of drip loops (Fig. 3) is an additional best practice. The next thing is to heat-shrink the connector fittings and alternate wrappings of electrical tape and butyl self-adhesive rubber tape to protect against moisture intrusion into the connector.
Maintaining door seals is incredibly important. Door seals should be inspected to make sure 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 finally, seals ought 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 if the conduit penetrations are perfectly sealed, the conduits continue to be going 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 Dehumidifying Dry Cabinets can transfer water vapor right into 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 less of a problem. The problem occurs when the enclosure temperature drops (as a result of equipment being de-energized, cooler nighttime temperatures, cooler weather conditions, etc.) and the temperature inside xakleh enclosure drops beneath the dew point, leading to condensation.
Expanding polyurethane foam sealant (Fig. 4) gives an excellent method of sealing around conduit cabling: It’s been found to be superior to silicone, primarily because caulking guns used with silicone are hard to insert far enough to the conduit to accomplish a highly effective seal. An expanding foam nozzle attachment can be inserted further into the conduit to create a powerful seal around the cabling.