Outdoors, or in wet indoor environments like wash-down areas, Electronic Dry 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 targets a number of these best practices.
Assume your enclosure will leak. Unless the applying requires a vented enclosure (e.g., for heat dissipation, battery off-gassing), a sealed enclosure represents the initial 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 best to assume 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 needs to be avoided. Even if Myers hubs or sealing locknuts are used for code compliance, enclosure penetrations ought to be made below energized parts, if at all possible.
In terms of cable penetrations (versus conduit penetrations), directing water out of the electrical enclosure or housing with the use of drip loops (Fig. 3) is another best practice. The next task is to heat-shrink the connector fittings and alternate wrappings of electrical tape and butyl self-adhesive rubber tape to guard against moisture intrusion to the connector.
Maintaining door seals is incredibly important. Door seals needs to 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 of 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 following best practice for Moisture Control Cabinets of electronics assumes that even in the event the conduit penetrations are perfectly sealed, the conduits are still 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 Desiccant Dry Cabinets can transfer water vapor right into a sealed enclosure. Typically, when electronics are energized, heat is generated as well as the air within the enclosure can hold even more moisture than ambient conditions, meaning water vapor is a lesser problem. The situation takes place when the enclosure temperature drops (as a result of equipment being de-energized, cooler nighttime temperatures, cooler climatic conditions, etc.) as well as the temperature inside xakleh enclosure drops underneath the dew point, causing condensation.
Expanding polyurethane foam sealant (Fig. 4) provides an excellent method of sealing around conduit cabling: It’s been found to get superior to silicone, primarily because caulking guns used in combination with silicone take time and effort to insert far enough into the conduit to accomplish a powerful seal. An expanding foam nozzle attachment can be inserted further into the conduit to create a powerful seal round the cabling.