Match your enclosure to the water and corrosion it meets, and the chart sorts itself out: Type 1 for a dry indoor wall, Type 12 for indoor dust and drips, Type 3R for rain, Type 4X for hose-down and washdown, Type 6P only when the box actually goes under water. Types 7 to 10 belong to classified areas, which take a specialist build we do not make. Two decisions always follow the Type. The alloy is one: no Type names a metal, and chlorinated washdown sends you to 316L. The size is the other: a rating says nothing about watts, so a 20 W panel still needs a box that holds 40 C inside. Every rating here is a manufacturer rating; our stainless boxes carry NEMA 4X / IP66 and are not UL listed.
Match the Type to the water in the room
Read down the table until a row describes your box's life; that row is the Type for your drawing. The definitions come from NEMA's enclosure types document — the association writes the definitions and does not test boxes. In the US, NEC 110.28 lists which Type suits which location, and an IP code on its own does not satisfy a specification written around a Type. Where the drawing crosses borders, carry both codes: the IP-to-NEMA conversion pairs them, and the IP code basics explain what each digit is tested for.
| The box faces | Type | The rating covers | Keep in mind |
|---|---|---|---|
| A dry indoor wall | 1 | Contact with live parts, falling dirt | No water protection at all |
| Drips from a leaky ceiling indoors | 2 | Falling dirt and dripping water | No rain, no hose |
| Dusty indoor air (flour, textile, cement) | 5 | Airborne and settling dust | Indoor duty only, by definition |
| Coolant and oil splash at the machine | 13 | Oil-tight, dust-tight indoor duty | Not for outdoor weather |
| General indoor dust and drips | 12 | Circulating dust and dripping liquids | The usual indoor plant panel |
| Rain and sleet outdoors | 3R, or 3RX near salt | Falling rain, sleet, external icing | No windblown dust, no hose |
| Windblown dust with rain outdoors | 3, 3S or 3X | Windblown dust, rain, sleet | 3S keeps the handle workable under ice |
| Hose-down and washdown | 4, or 4X with corrosion | Water thrown from any direction | No submersion, no hot high-pressure jets |
| Brief submersion | 6 | Short immersion at shallow depth | Not continuous immersion |
| Deep or continuous immersion | 6P | Prolonged submersion, depth agreed with the maker | Write the depth on the drawing |
| Flammable gas or vapor zones | 7 or 8 | Class I explosion protection | A classified-area specialist build |
| Combustible-dust zones | 9 or 10 | Class II dust-ignition protection | A classified-area specialist build |
The full definitions sit in the NEMA types guide; the rest of this article turns them into a pick by environment, metal and size.
Indoors: from Type 1 to Type 13
Type 1 is the bare box: it keeps fingers off live parts and sheds falling dirt, and it stops there. Type 2 adds dripping water and light droplets, which suits a wall under an old roof. Type 12 is the indoor workhorse — a gasketed door against circulating dust and dripping liquids — and it earns its keep wherever the air carries dust or the ceiling sweats. Type 13 sits on machine bases, where oil and coolant splash the walls. Type 5 covers dusty indoor air, and NEMA keeps it indoor-only, so dusty outdoor duty moves to Type 3. None of the five covers a hose: wash water finds gaps a Type 12 gasket was never tested for. When the room is dry but the panel still sweats overnight, the water is usually condensation, not the rating.
Outdoors: rain, dust and the X suffix
Type 3R is the rain box: it takes falling rain, sleet and external icing, and it says nothing about windblown dust. Type 3 adds windblown dust to the rain and sleet; Type 3S keeps the external operating handle workable while the box is iced over. The X suffix is the corrosion add-on: NEMA 250 puts Types 3X, 3RX, 3SX, 4X and 6P through 200 hours of salt spray, judged against an AISI 304 stainless specimen. A coastal wall or a road salted every winter therefore starts at 3RX, and a box that ever meets a hose skips 3R entirely and moves to Type 4. The rain-versus-hose split is worked through in NEMA 3R vs NEMA 4.
Hose-down and washdown: Type 4 and Type 4X
Type 4 is the washdown rating: water thrown from any direction, which covers a hosed floor and most sanitizer spray. Type 4X carries the same water tests plus the salt spray, so corrosive washdown always lands on 4X. On international drawings the pair is IP66 — jets through a 12.5 mm [0.49 in] nozzle at 100 L/min from 2.5 to 3 m [8 to 10 ft] for at least 3 min. A NEMA 4X rating has no hot high-pressure jet test; when the spec calls for IP69K, with 80 C [176 F] water at 80-100 bar, the box needs a rating marked for it, as the IP69 washdown rating explains. The rating also survives only as a system. Every gland, window and field-cut hole carries its own seal, and the lowest one sets the assembly's, as what a panel keeps after you cut it works through. One habit worth keeping: lock out and verify absence of voltage before anyone opens a door after a washdown.
Under water: Type 6 and Type 6P
Type 6 covers brief submersion; its nearest code, IP67, draws the line at 1 m [3 ft] for 30 min. Type 6P is the prolonged rating, nearest IP68, where the depth and duration are what the manufacturer and user agree and put in writing. Flood-prone pits, sumps and tanks call for 6P with the depth stated on the drawing; a box that only risks an occasional splash stays at 4X, because 6P construction costs more than a splash deserves. Keep the pairs straight: 6 with IP67, 6P with IP68. For deep or continuous submersion, the continuous-submersion limits article walks through depth, duration and what to confirm before you order.
Classified areas: Types 7 to 10
Types 7 and 8 serve Class I areas — flammable gases and vapors — and Types 9 and 10 serve Class II combustible-dust zones. These enclosures are part of an explosion-protection design: heavier walls, sealed openings and a certification trail a washdown stainless box never carries. We build stainless Type 4X boxes and do not build hazardous-location enclosures. Where a plant mixes both — say a food plant with a dust zone over the mills — the washdown panel sits outside the classified line, and the in-zone boxes come from a hazardous-location specialist.
The metal is a separate decision: 304 or 316L
A Type never names an alloy, so the 4X stamp means the same water tests on a 304 box and on a 316L box. Chlorides decide the metal. Salt air, brine, blood and chlorine-based sanitizers all leave chloride deposits, and 304 pits at room temperature under a chloride film or inside a gasket crevice. Both grades reach chloride stress-corrosion cracking around 60 C [140 F], and the molybdenum in 316L lifts pitting and crevice resistance without moving that threshold. So the pick is short: rain, fresh water and a dry indoor plant take 304; sanitizer washdown, coastal air or food-plant duty take 316L. The 304 vs 316L guide carries the grade-by-grade comparison, and why 316L still rusts covers the washdown habits that keep either grade clean.
Sizing a Type 4X box for a 20 W load at 30 C ambient
Inputs. A washdown corner panel runs a compact PLC, a 24 V DC power supply at light load and I/O terminals — call it 20 W of heat (example load; put your own device dissipation in). The plant floor sits at 30 C (example ambient). Drives and most electronics are rated for 40 C ambient unless a named datasheet allows more, so the inside air has to stay at or below 40 C. Stainless walls pass heat at k = 3.7 W/m²K, the value our heat guides use. Two catalog candidates fit the job: 16 x 12 x 8 in and 24 x 20 x 8 in (H x W x D), both inside the 6 x 4 x 4 in to 60 x 36 x 16 in range we build.
Rule. At steady state the box sheds its load through the walls at k per square metre per kelvin of difference, so temperature rise = load ÷ (k × area). Count the four sides and the top; leave out the back, which the wall blocks.
Small box. 16 x 12 x 8 in is 0.41 x 0.30 x 0.20 m. Area = 2 × (0.41 × 0.30 + 0.41 × 0.20 + 0.30 × 0.20) - 0.41 × 0.30 = 2 × 0.265 - 0.123 = 0.41 m². Rise = 20 W ÷ (3.7 W/m²K × 0.41 m²) = 20 ÷ 1.52 = 13 K. Inside air = 30 + 13 = 43 C, which is 3 K over the limit.
Bigger box. 24 x 20 x 8 in is 0.61 x 0.51 x 0.20 m. Area = 2 × (0.311 + 0.122 + 0.102) - 0.311 = 2 × 0.535 - 0.311 = 0.76 m². Rise = 20 ÷ (3.7 × 0.76) = 20 ÷ 2.81 = 7 K. Inside air = 37 C, with 3 K of margin.
Decision. At 20 W and 30 C ambient, order the 24 x 20 x 8 in box; the 16 x 12 x 8 in box runs 43 C inside and fails a 40 C-rated drive. The small box stays in play up to about 15 W (1.52 W/K × 10 K), the larger one up to about 28 W (2.81 × 10). Past those loads, add a heat exchanger or an air conditioner sized for the extra watts, because a filter fan drops the assembly below Type 4X.
What goes on the order
One line settles the choice: dry indoors takes Type 1 or 12, rain takes 3R, a hose takes 4X, water over the box takes 6P, and a classified zone takes a specialist. Here is that decision as an order sheet for a washdown box like the worked example:
| Line | What to write |
|---|---|
| Rating | Manufacturer-rated NEMA 4X / IP66; not UL listed |
| Material | 316L where sanitizer or salt sprays; 304 for rain and fresh water |
| Size | 24 x 20 x 8 in (H x W x D) for the 20 W example; any size from 6 x 4 x 4 in to 60 x 36 x 16 in |
| Door and mount | Hinged gasketed door, removable mounting panel, wall-mount feet |
| Cutouts | Every gland and window per drawing, each device carrying its own IP66 seal |
Set the inside layout with the enclosure selector, which filters by environment, listing need, inside size and DIN module count, or browse sizes in the stainless size finder. We build to order and deliver in 10 business days anywhere in the world, counted from drawing approval for custom work. Send the environment with the order — water, chemicals, sun — because that line, not the biggest number on the chart, is what picks the box.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 316L stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 316L stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 316L stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 316L stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Which gasket survives a chlorinated washdown?
EPDM is the usual pick: it spans about -50 to 150 C and holds up in hot water, steam and caustic. Nitrile resists oils up to about 120 C but swells in hot water, and silicone runs from about -60 to 200 C while wearing fast on abrasion. So EPDM on a washdown door, nitrile where oil splash rules, silicone only where heat rather than scrubbing is the enemy.
Is a NEMA 4X rating the same as IP66?
Close enough to pair on one drawing: NEMA publishes its own conversion (Table A-1 in its enclosure types document), and manufacturer-rated NEMA 4X / IP66 is the pair our stainless boxes carry; not UL listed. The conversion runs one way only, so an IP66 code alone never implies a Type, and US work still names the Type under NEC 110.28. Type 6 pairs with IP67 and 6P with IP68.
How deep can a Type 6P enclosure go?
As deep as the drawing states, because IP68 sets the depth and duration by agreement between manufacturer and user rather than by a fixed number. NEMA 6P also shares the 200-hour salt-spray test with 4X. For a sump or lift-station pit, write the realistic flood depth and time; 1 m for 30 min is the Type 6 boundary, not the 6P one.
Do Types 7 to 10 add washdown protection?
They add explosion protection instead: Types 7 and 8 cover Class I gases and vapors, and 9 and 10 cover Class II combustible dust, with heavy walls and sealed openings a Type 4X box never carries. A washdown plant with a classified zone puts the stainless 4X panel outside the zone and hazardous-location boxes inside it, which we do not build.
