Outdoors, or in wet indoor environments like wash-down areas, Electronic Dry Cabinets of electronic systems start out with the design of the enclosures and penetrations, and end with the design and configuration of the components. This short article concentrates on 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 very first line of defense against moisture. Unfortunately, even the very best NEMA 4 electrical enclosure works well until poor installation practices or out-year modifications create poorly sealed penetrations (Fig. 1).
It’s better 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 ought to be avoided. Even if Myers hubs or sealing locknuts are employed for code compliance, enclosure penetrations needs to be made below energized parts, if at all possible.
When it comes to cable penetrations (versus conduit penetrations), directing water out of the electrical enclosure or housing with 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 guard against moisture intrusion into the connector.
Maintaining door seals is essential. 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 should 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 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 into a sealed enclosure. Typically, when electronics are energized, heat is generated and the air in the enclosure can hold even more moisture than ambient conditions, meaning water vapor is a lesser problem. The issue takes place when the enclosure temperature drops (because of the equipment being de-energized, cooler nighttime temperatures, cooler climatic conditions, etc.) and the temperature inside xakleh enclosure drops beneath the dew point, resulting in condensation.
Expanding polyurethane foam sealant (Fig. 4) provides an excellent method of sealing around conduit cabling: It’s been found to become better than silicone, primarily because caulking guns used in combination with silicone are hard to insert far enough in to the conduit to accomplish an effective seal. A growing foam nozzle attachment can be inserted further in to the conduit to create an effective seal around the cabling.