Short answer: NEC 110.28, Table 110.28. The code names the equipment that must carry an enclosure type number, and the table lists Types 1 through 13 against the conditions each one covers — rain, dust, ice, hose-directed water — outdoor use on top and indoor use below. For a washdown area the table points at Type 4X: the same water tests as Type 4 plus a corrosion test. This page walks through what the table contains, which number your environment needs, why an IP66 mark alone falls short on a US drawing, and what to write on the order.
Where does the NEC list NEMA enclosure types?
NEC 110.28 is the place: its Table 110.28 lists enclosure Types 1 through 13, the conditions each protects against, and the equipment it applies to. Turn there first when a specification, a drawing or an inspector asks which type a box must carry.
NEC 110.28 covers enclosures for the equipment it names — switchboards, switchgear, panelboards, industrial control panels, motor control centers and the like — rated 1000 V nominal or less. It has each of those enclosures marked with a type number from the table. Pick the row that matches your environment, write that number on the drawing, and the inspector can trace it straight back to the code.
Older books file the same list under the pre-2011 numbering; the 2011 NEC moved the section to 110.28, so a 2008 book shows a different section number for the same table. The types themselves come from NEMA 250, the National Electrical Manufacturers Association standard that defines every type and its test. The NEC names the numbers, NEMA writes what they mean. The NEMA enclosure types guide walks through all thirteen.
What does Table 110.28 actually show for each type?
The table reads like a matrix: the rows are type numbers, the columns are conditions such as rain, dust and hose-directed water, and a mark in the box says the type covers that condition. It stacks two lists — enclosures for outdoor use on top, indoor use below.
The outdoor list carries the Type 3 family — 3, 3R, 3S, 3X and the newer RX and SX variants — plus Types 4, 4X, 6 and 6P. The indoor list carries Types 1, 2, 5, 12 and 13, and Types 4, 4X, 6 and 6P reappear there because they suit either location. Read down the columns and most panel work sorts itself out: rain outdoors points at 3R, dust and dripping liquids indoors at 12, hose-directed water at 4 or 4X.
The working set, with the jobs each row fits:
| Type | What the table's row covers | Typical job |
|---|---|---|
| 3R | Rain and sleet, indoor or outdoor | Unattended outdoor boxes away from any hose |
| 4 | Hose-directed water, indoor or outdoor | Washdown panels in food, beverage and wash-bay areas |
| 4X | Type 4 water plus a 600 h salt-spray corrosion test | Sanitizer, brine or coastal washdown |
| 6 | Temporary submersion: 6 ft [1.8 m] for 30 min | Pits and vaults that flood briefly |
| 6P | Prolonged submersion at a stated depth and duration | Continuously wet or submerged equipment |
| 12 | Dust, dirt and dripping liquids, indoor | Dry plant-floor panels |
The 6 ft [1.8 m] and 30 minute figures are NEMA 250's Type 6 design test; Type 6P is tested at a depth and duration the manufacturer states. Types 7, 8, 9 and 10 cover Class I and Class II hazardous (classified) locations, and those areas are designed under the NEC's classified-location Articles rather than by box type — we do not build those types. Which row a starter, a junction box or a motor needs, box by box, is the subject of the NEC enclosure type requirements article.
Which type does a washdown or hose-down area need?
Pick Type 4 for hose-directed water and Type 4X when that water is corrosive — sanitizers, brine, coastal salt air. Table 110.28 shows both covering the hose column. The X adds NEMA 250's 600 h salt-spray corrosion test, which is why food, marine and chemical washdown panels specify 4X.
NEMA 250's Type 4 hose test is the number to picture: a 1 in [25 mm] nozzle throwing 65 US gal/min [about 246 L/min] at the enclosure from at least 10 ft [3 m], for at least 5 minutes. That is a washdown gun at working distance, not rain or splashes. It is why a Type 12 or 3R box never substitutes on a washdown line. Type 4X runs the same water tests and then must survive 600 hours of salt spray under NEMA 250's corrosion test; a plain Type 4 box never faces that exposure.
Material follows the water: fresh-water washdown on a food line usually accepts 304 stainless, while brine, chlorides or salt air push the order to 316L. The water tests, the corrosion test and the IP66 question sit side by side in the NEMA 4 vs 4X vs IP66 guide.
Does an IP66 rating satisfy Table 110.28?
NEC 110.28 states that "IP ratings are not a substitute for Enclosure Type ratings," so an IP66 stamp alone fails a US specification that calls out Type 4X. Order a box that carries both codes: the type number for the inspector, the IP code for international drawings.
The two schemes test different water. Worked example: the Type 4 hose test pushes 65 US gal/min through a 1 in nozzle from 10 ft. Converting, 65 gal/min × 3.785 L/gal = 246 L/min. The IPX6 jet test in IEC 60529 uses a 12.5 mm nozzle at 100 L/min from 2.5 to 3 m. So 246 L/min ÷ 100 L/min = 2.5: the US hose test throws about two and a half times the water the European jet test does. A panel specified from the code table therefore demands more water performance than an IP66 certificate shows on its own. The IP code also tests no corrosion and no icing, while the NEMA table covers both.
Immersion does not buy jet protection either: the IPX7 test holds 1 m [3.3 ft] of water for 30 minutes and says nothing about jets. The schemes measure different things, so the pairs are read side by side, not converted — the IP to NEMA conversion article and the IP rating chart guide show where they line up and where they stop.
Who writes the tests behind each type number?
NEMA 250 writes the definitions and the design test behind every type. UL 50E is the standard a lab evaluates an enclosure to when a project needs a listed box. The code table points at the type; these two documents decide what survives the test floor.
NEMA publishes the definitions and the tests, and NEMA does not test, certify or endorse enclosures — the manufacturer rates its own box against the standard. A UL listed enclosure has been evaluated by UL to UL 50E. In US workplaces, OSHA 1910.303(a) requires electrical equipment to be approved, and 1910.399 defines acceptable equipment as that accepted, certified, listed, labeled or otherwise determined safe by a nationally recognized testing laboratory. Our enclosures are rated NEMA 4X / IP66 by the manufacturer and are not UL listed — the type number and the tested performance tell the same story, and the third-party mark is what differs. When a specification asks for the mark, the UL 50E vs NEMA 250 guide sets out what that means and what to ask for.
What does the type number change on a real panel?
Three places carry the number in practice: the drawing's specification line, the finished panel's nameplate, and the box you order. NEC 409.110 requires an industrial control panel's marking to include an enclosure type number, so the row you pick in Table 110.28 ends up stamped on the door.
UL 508A is the standard for listing an industrial control panel — NEC 409.2 defines the panel as two or more power circuit components, control circuit components, or both, assembled. The marking rule keeps the type visible for the panel's life. The chain from table to nameplate, and the NEC compliance questions around it, is what the NEMA enclosure ratings and NEC compliance for industrial control panels page covers.
The number also has to survive your cutouts. Every gland, window and operator added afterwards carries its own rating, and the assembly keeps Type 4X only when each added part matches it — the what a panel keeps after you cut it and mount devices article works through that rule part by part. A gland rated IP54 drops the whole assembly to IP54, whatever the door label says.
What do you write on the order?
Write the type before the material: "Type 4X washdown enclosure, 316L stainless, cutouts per attached drawing." A one-piece custom box in 304 or 316L is delivered in 10 business days from drawing approval; the types used in classified areas are not part of our catalog.
Width, height, depth and every cutout are yours to set, from a single piece. Match the row to the room, then the material to the water:
- Dry indoor panel, dust and dripping liquids: Type 12.
- Outdoor rain and sleet, no hose work: Type 3R.
- Hose-directed washdown in ordinary water: Type 4, usually 304 stainless.
- Washdown with sanitizers, brine or salt air: Type 4X in 316L.
- Brief flooding to 6 ft [1.8 m]: Type 6, temporary submersion.
- Standing or prolonged submersion: Type 6P as a custom build — send depth, duration and fluid with the inquiry, and feasibility is confirmed against them before the drawing is cut.
If you are sorting stock sizes against a custom build, the enclosure selector filters by environment, listing and usable inside dimensions. For a one-piece box in your own size, custom stainless enclosures is the route, and the spec line above is enough to start a quote. A sample line for a food-plant washdown panel: "Enclosure, 1 piece, 316L stainless, manufacturer-rated NEMA 4X / IP66, cutouts per drawing."
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 |
|---|---|---|---|
| 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 |
| 24 × 20 × 8 in | 316L stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 316L stainless | 16 x 14 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
My older code book shows the enclosure table under a different section number — what changed?
The 2011 NEC renumbered the section; editions printed before that list the same enclosure table under the pre-2011 numbering. The content and the decision are unchanged: match the type to the environment in Table 110.28, then quote the table by its current number.
Does a Type 4X enclosure have to be stainless steel?
No — NEMA 250 defines 4X by performance: the full Type 4 water suite plus a 600 h salt-spray corrosion test. Fiberglass and polycarbonate boxes can carry the same type. Material is a separate line on the order: 304 stainless suits most washdown plants, 316L suits chlorides, brine and salt air.
Is a Type 4X box enough for a pit that floods twice a year?
No — 4X is a hose-down rating, and immersion is a different test. Temporary submersion is Type 6, tested in 6 ft [1.8 m] of water for 30 minutes; longer or deeper immersion is Type 6P, built custom to the stated depth, duration and fluid. Send those three numbers with the inquiry and feasibility is confirmed before the drawing is cut.
What type number belongs on the nameplate of a built control panel?
NEC 409.110 requires an industrial control panel's marking to include its enclosure type number, so the value comes from Table 110.28 — Type 4X for a washdown panel, Type 12 for a dry indoor floor. The assembled rating holds only if every gland, window and operator added to the box matches it too.
Can I leave the IP code off a US drawing and specify only the NEMA type?
You can — NEC 110.28 and its table speak only in type numbers. Keeping both costs nothing extra on our builds: our 304 and 316L enclosures are rated NEMA 4X / IP66 by the manufacturer and not UL listed, so one order line serves the code official and the international reviewer alike.
