The short answer
- NEMA 3R: rain, sleet and snow stay out; undamaged by external ice. Not rated for windblown dust or hose-directed water, and it may be ventilated and must have drainage.
- NEMA 3: as 3R plus windblown dust. 3S: as 3, and external mechanisms still work when iced over.
- NEMA 4: adds splashing and hose-directed water to windblown dust, rain and ice. X versions (3RX, 3X, 3SX, 4X) add a corrosion test.
- Choose 3R for sheltered rain-only spots, 3 or 4 where wind carries dust or sand, and 4 or 4X wherever a hose, sprinkler or pressure washer can reach the enclosure.
The outdoor family at a glance
NEMA 250 covers enclosures for equipment up to 1000 V. Its outdoor types, paraphrased from NEMA's definitions, with the IP code each meets or exceeds from NEMA's conversion table:
| Type | Rain, sleet, snow | Windblown dust | Hose-directed water | Ice | Corrosion test | Meets or exceeds |
|---|---|---|---|---|---|---|
| 3R | Yes | No | No | Undamaged | Outdoor | IP24 |
| 3RX | Yes | No | No | Undamaged | Additional | IP24 |
| 3 | Yes | Yes | No | Undamaged | Outdoor | IP55 |
| 3X | Yes | Yes | No | Undamaged | Additional | IP55 |
| 3S, 3SX | Yes | Yes | No | Mechanisms operable when ice laden | Outdoor / additional (3SX) | IP55 |
| 4 | Yes | Yes | Yes | Undamaged | Outdoor | IP66 |
| 4X | Yes | Yes | Yes | Undamaged | Additional | IP66 |
All of these may also be used indoors. NEMA's outdoor comparison table flags 3R and 3RX as types that may be ventilated. The full list of types, including the indoor ones, is in NEMA enclosure types, and the conversion to IP codes in the IP rating chart.
Rain test vs hosedown
The core difference is how the water is applied and what may get in.
- Type 3R, rain test. Under NEMA 250-2018, nozzles at 5 psi spray the top and exposed sides at a 45° angle. A small amount of water may get in, provided it does not accumulate and does not reach a level higher than the lowest live part.
- Type 3, water test. NEMA's comparison of its water tests lists a 1 in (25.4 mm) nozzle at 45 gal/min (170 L/min), 10 to 12 ft (3.0 to 3.7 m) away, moved along seams, joints and mechanisms at 0.25 in/s. No ingress is allowed. This is Type 3's rain-type water test, at a lower flow than Type 4's 65 gal/min hosedown, which is why the table does not credit Type 3 with hose-directed water.
- Type 4, hosedown. The same nozzle and distance at 65 gal/min (240 L/min), aimed along every seam, joint and mechanism. No ingress is allowed.
Hence the descriptive words that turn up in specifications. One enclosure maker's glossary uses "rainproof" for Types 3R and 3RX (beating rain does not interfere with operation or wet live parts), "rain-tight" for Types 3, 4, 4X and 6 (rain does not enter), and "water-tight" for Types 4, 4X and 6 (a stream of water does not enter).
A 3R enclosure is therefore wrong anywhere it can be hit by a hose, a pressure washer, a lawn sprinkler or vehicle spray. Those need Type 4 at least.
Windblown dust and sand
NEMA's definition of Type 3R lists protection against falling dirt only. Types 3, 3S and 4 add windblown dust. A manufacturer's data sheet for a 3R enclosure states it plainly: Type 3R is not intended to protect against dust, internal condensation or internal icing. On farms, quarries, construction sites, roadsides and desert installations where wind carries grit, choose Type 3 or 4 rather than 3R.
Drain holes and ventilation
Type 3R keeps water out by shape, not by a full seal, so it is expected to let water out again. UL 50E / CSA C22.2 No. 94.2 requires Types 2, 3R and 3RX to have provisions for drainage. NEMA 250 and UL 50E both set the size: drainage openings "shall not be less than 3.2 mm in diameter (1/8 inch in diameter) or more than 6.4 mm in diameter (1/4 inch in diameter) unless baffled or provided with a drainage fitting". Where a 3R enclosure is also rated as another type, its drain openings are closed with a removable plug and instructions are provided with it.
For field-drilled drains, NEC 314.15 permits approved drainage openings of 3 mm (1/8 in) to 6 mm (1/4 in) in boxes and conduit bodies listed for damp or wet locations; check the edition your authority having jurisdiction enforces. NEMA's guidance on that rule says a drain should be drilled only in the underside at the lowest point, and never where the opening could jeopardize the enclosure's type rating. In practice: never drill an unbaffled hole in a Type 4 or 4X enclosure. If a sealed enclosure needs to drain or breathe, use a drain or breather fitting rated for the same type.
Ice: undamaged vs operable
Types 3, 3R, 4 and their X versions must be undamaged by ice forming on the outside. That does not mean a disconnect handle or latch will still work while encased in ice. Only Types 3S and 3SX promise that external mechanisms remain operable when ice laden, and UL 50E adds that those mechanisms must support the extra weight of ice and withstand removal of the ice with a hand tool.
NEMA 250 checks this with an external icing test in a cold room. A manufacturer's abridged description of an earlier edition of the standard gives the method as spraying water until 19 mm (3/4 in) of ice has built up on a 25 mm (1 in) metal test bar, then holding about -5 °C for 3 hours; the current edition's details may differ. If an operator must be able to throw a disconnect in freezing rain, specify Type 3S or 3SX for that mechanism, or a hood that keeps ice off it. Type 4 alone does not cover it.
Corrosion: what the X adds outdoors
All outdoor types are exposed to 600 hours of salt spray, alongside a G90 galvanized sheet steel specimen they are compared with. For ferrous Type 3R enclosures, NEMA 250-2018 calls for corrosion protection by hot-dipped galvanized sheet steel to coating designation G90. The X types (3RX, 3X, 3SX, 4X) then get another 200 hours of salt spray and are compared with an AISI 304 stainless steel specimen.
Coastal sites, road salt, wastewater plants and chemical areas call for an X type. Stainless is the usual way to meet 4X; for salt air 316L is often the better grade. The corrosion test itself is explained in NEMA 4 vs 4X vs IP66.
Condensation and conduit water
No outdoor type stops condensation. NEMA 250's scope leaves conditions inside the enclosure, such as condensation, outside the standard, and the NEC notes that type-rated enclosures are not intended to protect against water, including condensation and icing, that forms inside or enters through a raceway. An outdoor enclosure that warms by day and cools at night breathes humid air in through every gap. A vented 3R enclosure exchanges air freely; a sealed Type 4 traps whatever moisture is inside. Seal conduit runs from warm buildings, keep cable entries on the bottom face, and plan heat and drainage; see enclosure condensation and outdoor electrical enclosures.
How to choose
| Location | Minimum to ask for |
|---|---|
| Rain and snow only, no windblown dust, no hose | 3R |
| Wind carries dust, sand or grit | 3, or 4 if it may also be hosed |
| Disconnect or latch must work when iced over | 3S / 3SX |
| Hose, sprinkler, pressure washer or vehicle spray | 4 |
| Coastal, road salt, wastewater, chemicals | 4X (or 3RX for rain-only) |
| Pits, flood zones, possible submersion | 6 / 6P |
The rating only holds with every opening closed by a fitting rated at least as high as the enclosure: NEMA's weakest-link rule applies outdoors too. Our cutouts and glands guide covers conduit hubs and glands.
Custom builds. NEMA4 Enclosure builds custom outdoor enclosures in 304 or 316L stainless, powder-coated carbon steel (RAL 7035; other colours on request), aluminum, polycarbonate or fiberglass (the non-metallics in standard molded sizes, cut to your layout), with NEMA types 3R, 4, 4X or 6P as manufacturer ratings for the specified design, from one piece. Our standard wall-mount enclosures are manufacturer-rated NEMA 4X-type / IP66 - not UL listed. Custom work is quoted by email and delivered in 10 business days from drawing approval.
Frequently asked questions
What is the difference between NEMA 3R and NEMA 4?
Type 3R keeps out falling rain, sleet and snow and is undamaged by ice, but is not rated for windblown dust or hose-directed water. Type 4 adds windblown dust, splashing and hose-directed water, with no water allowed inside in the hosedown test.
Is NEMA 3R waterproof?
No. Type 3R is rainproof: in the rain test a small amount of water may enter as long as it does not accumulate or rise above the lowest live part. It is not tested against a hose stream or submersion.
Can a NEMA 3R enclosure have drain holes?
It must have provisions for drainage. NEMA 250 and UL 50E limit drainage openings to 3.2 to 6.4 mm (1/8 to 1/4 in) in diameter unless they are baffled or fitted with a drainage fitting.
Is NEMA 3R dust-tight?
No. NEMA's definition of Type 3R covers falling dirt only. For windblown dust choose Type 3, 3S or 4, which NEMA's conversion table shows meeting IP55 or IP66 rather than IP24.
Do I need NEMA 3S for icing?
Only if an external mechanism, such as a disconnect handle, must work while covered in ice. Types 3, 3R and 4 only have to be undamaged by external ice; Types 3S and 3SX must stay operable.
Sources
- NEMA, "NEMA Enclosure Types" (Type 3, 3R, 3S, 3X, 3RX, 3SX, 4, 4X definitions; Table 2 outdoor comparison and ventilation note; Table A-1 conversion to IP)
- NEMA, "NEMA FAQs: Enclosures" (Q13 Type 3 and Type 4 water test parameters, Q14 salt spray, Q15 weakest link)
- ABB technical note 1VAL0001-TN, NEMA 250-2018 Type 3R vs IEEE C37.20.2 (1000 V scope, rain test parameters and acceptance, G90 protection)
- NEMA Technical Services Bulletin No. 110, drain openings in boxes and conduit bodies (NEC 314.15; NEMA 250 / UL 50E drainage opening size for Types 3R and 3RX)
- TÜV Rheinland test report CN25IYGM 001 (quotes UL 50E / CSA C22.2 No. 94.2 clauses on drainage, ice-laden mechanisms on Types 3S and 3SX)
- Rockwell Automation, Bulletin 1500 Type 3R enclosure product data (3R not intended for dust, internal condensation or icing; abridged NEMA 250 icing test of an earlier edition)
- nVent HOFFMAN, Spec-00486, Standards organization summary (rainproof, rain-tight and water-tight glossary)
- EC&M, "Understanding General Requirements of the NEC, Part 16" (2026): NEC 110.28 and water that enters through raceways or forms inside
- ANSI/NEMA 250-2020, contents and scope (condensation inside the enclosure not covered)