NEMA 4 protects against windblown dust, rain, sleet, snow, splashing, and hose-directed water under specified conditions. NEMA 6 adds protection against temporary submersion at limited depths. Selection depends not on indoor versus outdoor placement, but on whether water could rise above the base, door frame, or cable entries and persist over time.

If equipment only faces rainfall, washdowns, or short-term spray, NEMA 4 is often suitable. For low-lying areas, underground vaults, pump rooms, drainage zones, or locations prone to standing water, document the peak water level, rise rate, duration, and flow direction, then evaluate NEMA 6 or other submersible designs.

NEMA 6 enclosures demand close attention to door rigidity, latch compression, continuous gasketing, base construction, and cable glands. Hydrostatic pressure increases with depth, which can deform large doors or removable panels. NEMA 6 test results do not qualify an enclosure for deeper water, extended immersion, or continuous submersion; project documentation must define the actual test conditions.