Outdoors, or in wet indoor environments like wash-down areas, Electronic Dry Cabinets of electronic systems start out with the style of the enclosures and penetrations, and end with the design and configuration of the components. This article concentrates on a number 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 first line of defense against moisture. Unfortunately, even the very best NEMA 4 electrical enclosure works great until poor installation practices or out-year modifications create poorly sealed penetrations (Fig. 1).
It’s advisable to assume that penetrations into any enclosure will leak (as shown by Fig. 2). Based on 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 being used for code compliance, enclosure penetrations ought to be made below energized parts, if at all possible.
With regards to cable penetrations (versus conduit penetrations), directing water out of the electrical enclosure or housing through the use of drip loops (Fig. 3) is yet 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 safeguard against moisture intrusion to the connector.
Maintaining door seals is essential. Door seals ought 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 from the door may prevent a uniform seal. And finally, 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 Moisture Control Cabinets of electronics assumes that even when the conduit penetrations are perfectly sealed, the conduits remain 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 Dehumidifying Dry Cabinets can transfer water vapor right into a sealed enclosure. Typically, when electronics are energized, heat is generated as well as the air in the enclosure can hold even more moisture than ambient conditions, meaning water vapor is a lesser problem. The problem occurs when the enclosure temperature drops (due to the equipment being de-energized, cooler nighttime temperatures, cooler climate conditions, etc.) and also the temperature inside xakleh enclosure drops beneath the dew point, resulting in condensation.
Expanding polyurethane foam sealant (Fig. 4) provides an excellent approach to sealing around conduit cabling: It’s been found to be preferable over silicone, primarily because caulking guns combined with silicone are difficult to insert far enough in to the conduit to accomplish a powerful seal. An expanding foam nozzle attachment can be inserted further into the conduit to create an effective seal across the cabling.