Outdoors, or in wet indoor environments like wash-down areas, Low Humidity Control Cabinets of electronic systems start with the design of the enclosures and penetrations, and end with the design and configuration of the components. This article focuses on several of these best practices.
Assume your enclosure will leak. Unless the application form demands 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 most effective NEMA 4 electrical enclosure is effective until poor installation practices or out-year modifications create poorly sealed penetrations (Fig. 1).
It’s best to think that penetrations into any enclosure are going to leak (as shown by Fig. 2). According to 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 being used for code compliance, enclosure penetrations ought to be made below energized parts, if 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 step is to heat-shrink the connector fittings and alternate wrappings of electrical tape and butyl self-adhesive rubber tape to protect against moisture intrusion in to the connector.
Maintaining door seals is incredibly important. Door seals ought to 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 of the door may prevent a uniform seal. And lastly, seals should be inspected for pinching, tears and proper adhesion to original mating surfaces.
Assume all conduits contain moisture
The following best practice for Dry Cabinets For PCB Storage of electronics assumes that even in the event the conduit penetrations are perfectly sealed, the conduits continue to be likely 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 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 smaller 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, causing condensation.
Expanding polyurethane foam sealant (Fig. 4) offers an excellent method of sealing around conduit cabling: It’s been found to get better than silicone, primarily because caulking guns used in combination with silicone are hard to insert far enough in to the conduit to achieve a highly effective seal. An expanding foam nozzle attachment can be inserted further in to the conduit to produce a highly effective seal round the cabling.