It's tough enough getting electrical components, board design, and programming to finish in a well-timed sequence. It's worse when designers select enclosures as after thoughts. These are serious errors because engineers assume enclosures are low-tech items and most any will do. Such last minutes decisions lead designers to five frequent pitfalls. For instance:

Choosing the wrong NEMA rating for the application

A recent survey showed that over 70% of engineers were confused by the different NEMA ratings. A higher rating does not necessarily translate to higher environmental protection. Based on this survey, a second one was conducted that suggested up to 40% of all enclosures requiring protection are specified to the wrong level.

To be fair to engineers, the NEMA numbering system is inconsistent. For example, a NEMA 1 box is a basic enclosure that protects the user from accidentally touching the internal equipment. The unit can have ventilation or other openings, but those openings have to be small enough to keep fingers and other objects out. NEMA 12 enclosures are sealed to protect against falling dirt, circulating dust, fibers, and so on. It is a good choice for factories where liquids are not a concern. A NEMA 12 enclosure does not protect against liquids and is intended for indoor use only. For that you'll need a NEMA 4 enclosure, which can be used both indoors and outdoors, offers the same protection as NEMA 12, and protects against liquids and ice. Spec a NEMA 4 enclosure when the product is intended for a factory where there may be spray cleaning, or if the box will be used outdoors.

Choosing an enclosure made from the wrong material

Another pitfall is to automatically choose a metal enclosure. Metal is standard in the U.S. while plastic is more common in Europe and Asia. NEMA enclosures are available in a wide range of materials including various strength plastics, die-cast aluminum, fiberglass, and steel. Each has advantages and disadvantages based on the properties of the materials including weight, price, and durability. Selecting the proper material can save money, as well as enhance function.

The enclosure is too big or too small

Knowing the dimensions required for the total product and choosing a properly sized enclosure is not straightforward. An engineer may buy a larger NEMA rack when only a few items need protection. In this case, a smaller rack-mount NEMA enclosure could have been used, thus saving the cost of protecting the complete rack.

Alternatively, an engineer may fit components into an enclosure that is too small for the application. To save a few cents on an enclosure, extra design and assembly time is required that offsets the cost differential of a slightly larger enclosure.

Insufficient consideration to features that assist with the enclosure

Spending more for product features may cut significant costs during assembly, or provide features that support a higher selling price. For example, if the enclosure requires frequent access, a knob or key lock latch may be appropriate. For less frequent access, a more secure but less expensive screw closure might be acceptable. If the enclosure houses a controller then easy-to-mount wall brackets can save time and money. Another useful feature is a clear lid or body which lets end users see internal readouts without drilling access holes.

Failure to anticipate modifications

Finally, it's critical to anticipate how an enclosure may be modified. Most NEMA enclosures need some modification to allow for inputs and outputs. Some enclosures are easier to modify than others. Certain materials are more easily drilled to add lines. And steel or die cast aluminum are the logical choices when the application calls for a special color.