What enclosure should you pick?
Transfer switch enclosures primarily differ based on their intended installation location (indoor vs. outdoor) and the degree of protection they provide against environmental factors like water, dust, and corrosion.
These differences are defined by NEMA (National Electrical Manufacturers Association) ratings.
Common NEMA Ratings for Transfer Switches
| Rating |
|---|
| Use Location | Protection Against | Key Differences/Features | |
|---|---|---|---|
| NEMA 1 | Indoor only | Falling dirt; personnel access to hazardous parts | Basic indoor protection; no defense against water. |
| NEMA 3R | Indoor/Outdoor | Rain, sleet, snow, and external ice formation; falling dirt; personnel access | Common outdoor rating; includes drain holes to allow water to escape; cannot withstand hose-directed water. |
| NEMA 4 | Indoor/Outdoor | Windblown dust, rain, sleet, snow, and hose-directed water; external ice formation | Weatherproof and sealed from outdoor conditions; more robust seal than 3R. |
| NEMA 4X | Indoor/Outdoor | Same as NEMA 4, plus corrosion | Made from stainless steel or other corrosion-resistant materials, essential for coastal or humid environments. |
| NEMA 12 | Indoor only | Falling dirt, circulating dust, fibers, and light dripping/splashing water | Found in industrial settings; higher dust protection than NEMA 1, but still indoor-only. |
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