The commercial electronics market has traditionally used fixed, frame-type power supplies. But today's trend is toward plug-in power-supply modules, which are easily accessible and serviceable from the front of an enclosure. Telecom applications demand high reliability with N+1 redundant power supplies that are hot swappable for fast replacement in the event of a power-supply failure.
Higher-power requirements demand increased cooling. Thermal management is arguably the most important aspect of the enclosure design to ensure the reliable operation of its integrated electronics. Outdoor enclosures deploy heat exchangers, air conditioners, and removable solar shields to handle extreme environments. Indoor cabinet enclosures use many different forms of cooling.
Natural convection cooling is common in server cabinets, which customarily are low-power applications with perforated front/rear doors and top covers. Forced-air conduction cooling, however, is the most common form of thermal management for indoor cabinet enclosures and microcomputer systems. Some applications deploy evacuation, or "pull," cooling. Others use a "push" system. And, some combine the push and pull systems with air movers at the enclosure's intake and exhaust ports. The high reliability required by telecom systems generally demands that redundant, plug-in fan trays, which are hot swappable, be used.
Alarm monitoring for notification of fan failures also is very common in telecom systems. Air filters, mandated by telecom companies, must meet the NEBS Level 3 (GR-63-CORE) standards for airborne contaminants. Thermal-simulation software is available to accurately model electronics systems to determine cooling requirements.
Other important enclosure items to consider have to do with ease of movement and setting the enclosure in its final resting place. High-strength eye-bolts for lifting are commonly available at the enclosure's top four corners. Castors are provided for moving the enclosure without lifting. In some applications, removable castor assemblies are used to move it into position. Then, they're detached.
Also, ganging kits are available for joining enclosures side by side. Mechanical fixing of the enclosure to the installation site can be accomplished by providing an add-on base equipped with retractable castors and leveling feet. There's a standard floor-mounting pattern for telecom enclosures defined in NEBS GR-63-CORE. Anti-tip brackets are common for fixing server cabinets to the floor. More importantly, they prevent enclosure tip-over from telescoping heavy equipment.
While it may sound like you need an experienced packaging engineer on staff to specify the right enclosure for the application, a good idea is to partner early with a leading-edge supplier.
References:
Vitale, Pat, "Fitting Shielded Enclosures Into the Solution," Evaluation Engineering Magazine, p. 52, Feb. 1999. *