Short answer: build the open frame for a clean, dry, supervised indoor space on 24 V DC, and put a rated enclosure around your panel the day dust, hose water or weather arrive. A guarded frame gives IP2X at best: a jointed 12 mm test finger stays off live parts, while dust and water meet nothing in their way. A Type 12 box adds dust, lint and dripping-liquid protection indoors. A Type 4X box adds hose-directed water and corrosion resistance, which is what washdown and outdoor service need. The numbers below show where each build stops and what to put on your order.
What an open frame actually rates
A frame of T-slotted aluminum extrusion with a mesh guard carries no rating on paper. ANSI/NEMA 250-2020 defines the enclosure types, and manufacturers rate their own tested designs; NEMA writes the definitions and does not test or certify boxes. Our stainless enclosures, for instance, are manufacturer-rated NEMA 4X / IP66, not UL listed. A frame you bolt together sits outside that system, so start from "unrated" and treat every protection claim as your own to design in.
What the build can earn, with guards, is the bottom of both scales. ANSI/NEMA 250-2020 lists Types 1, 2, 5, 12, 12K and 13 as indoor types, and Type 1 covers incidental contact with the equipment plus falling dirt; real Type 1 boxes pass tests of their own, as what the Type 1 tests cover explains. On the IEC 60529 scale a first digit of 2 means a jointed test finger cannot reach hazardous parts, and it also excludes solid objects 12.5 mm and larger. what the Type 1 tests cover IP20 is that finger claim plus a second digit of 0: no water protection of any kind. IP2X keeps the finger claim and leaves water unaddressed. The finger-safety article walks the probe and the clearances in detail. what makes an enclosure finger safe
Two facts settle the paperwork in the US. NEC 110.28 states that IP ratings are not a substitute for enclosure Type ratings, and Table 110.28 matches each Type to the locations it suits, so US specs name the NEMA Type while international specs name the IP code. And there is no NEMA 0: an unguarded frame with exposed 120 V terminals sits below Type 1, in the NEC's guarding territory, which starts at 50 V.
The finger test, with numbers
IEC 60529 specifies the probe: a jointed finger 12 mm [0.47 in] in diameter and 80 mm [3.15 in] long. IP2X passes when that probe cannot touch a live part. Mesh is where shop-built panels fail, and the arithmetic decides it.
Worked example: a trainer panel guarded by true 1/2 in hardware cloth. The clear openings measure 12.7 mm, and 12.7 mm is wider than the 12 mm probe, so the tip enters. A terminal strip mounted 40 mm [1.6 in] behind the mesh sits well inside the probe's 80 mm reach, and the build fails IP2X. Two fixes work. Stand the strip off until the nearest live terminal sits 100 mm [4 in] behind the mesh, past the probe's length with margin for its jointed sweep. Or refit the guard with 1/4 in cloth: its 6.4 mm openings leave the probe outside at any depth, so the guard passes on geometry alone.
Mesh sold by pitch adds one trap. A 1/2 in pitch cloth woven from 0.063 in wire leaves openings of 0.5 − 0.063 = 0.437 in [11.1 mm], which blocks the probe outright even though the label reads half an inch. The gap between label and opening is 1.6 mm, and that is the difference between pass and fail. Count clear openings on your own guard, with calipers if the datasheet stays quiet.
The same panel, frame or rated box
| Question | Guarded open frame | Type 12 enclosure | Type 4X stainless enclosure |
|---|---|---|---|
| Rating on paper | none; behaves like IP2X | Type 12, indoor | NEMA 4X / IP66, manufacturer-rated |
| Fingers off live parts | yes, where the guard beats the 12 mm probe | yes | yes |
| Dust and lint | open to them | blocked | blocked |
| Water | none, IPX0 | dripping non-corrosive liquids | hose-directed water, any direction |
| Outdoors | unsuitable | no | yes |
| Corrosion | dry rooms only | painted steel, indoors | 304 or 316L stainless |
| Heat soak | none, air moves through | sealed: about 29 W for a 10 C rise in a 20 x 16 x 8 in box | same, with room for a filter fan or cooler |
| Lockable | no | yes | yes |
The heat cell assumes a 20 x 16 x 8 in stainless box at 25 C ambient; the arithmetic sits under the open-frame wins below.
What voltage an open frame can carry
Voltage sets how much guarding the frame needs at all. The NEC starts its live-part guarding rules at 50 V, so a frame carrying 24 V DC control circuits sits below the line: dress the wiring and keep terminals covered, and contact carries little risk. Put 120 or 240 VAC on the same frame and every terminal needs its own protection — finger-safe blocks with an IP20 claim from the maker's datasheet, shrouds or covers, or the whole line-voltage section in a small rated box beside the frame.
An IP20 PLC or drive tells the same story from the other side. The device is finger-safe out of its carton, and the frame adds nothing, so a clean lab is fine while a dusty floor is a failure; the IP20-device guide plans that exact move into protection. enclosure for an IP20 drive
One limit matters more than fingers. Mesh passes a probe; an arc fault is another matter, and a short in the open sprays molten copper across the bench. When arc energy is part of your design, the arc-flash article sets out when an arc-rated enclosure applies. arc flash rated enclosures
Where the open frame wins
Pick the frame when the panel lives where you can watch it:
- Training and teaching benches. 24 V DC circuits, supervised use, wiring that changes every week. The open view is the point, and rework costs an hour, not a door gasket.
- Demos and prototypes. A build you rewire every few days earns nothing from a gasketed door.
- Clean, dry indoor rooms. Offices and labs where dust wipes off and no hose ever appears; this is the honest home for the frame.
- Heat-sensitive builds. Air moves straight through, so nothing soaks. A sealed 20 x 16 x 8 in stainless box sheds only about 29 W for a 10 C rise at 25 C ambient: 1,216 in² [0.78 m²] of surface times 3.7 W/m²K for stainless walls times 10 K = 29 W. The same electronics on an open frame run near room temperature, and the sealed-box version needs that math plus maybe a fan or cooler.
Where the rated enclosure wins
Any one of these conditions ends the frame conversation, and each has a named box behind it:
- Dust. Fine dust settles on terminals, boards and relay contacts, and conductive dust tracks toward a fault. Type 12 blocks dust and lint indoors; the plasma-table enclosure guide shows what dust protection takes on a saw or cutting floor. plasma table computer enclosure
- Water. Hose-down, washdown and rain are Type 4 territory: hose-directed water from any direction. On the IEC scale that is the jet region — IPX5 at 12.5 L/min from a 6.3 mm nozzle, IPX6 at 100 L/min from a 12.5 mm nozzle. Temporary immersion is Type 6, and prolonged submersion is Type 6P.
- Weather. Outdoors you add sun, cold and the nightly dew cycle. The outdoor-rating checklist tells you which markings mean it, and the vent-versus-sealed decision decides how the box stays dry through that cycle. how to tell if an enclosure is outdoor rated enclosure vent or sealed box
- Condensation. A sealed box breathing with the night air fogs and drips; an anti-condensation heater holds the walls above dew point, and the heater article sizes one. anti-condensation heaters
- Corrosion. Salt air, brine and chlorides move the wall material from 304 to 316L stainless.
- Security. A rated box locks; a frame is open shelving with wires.
The decision by environment
| Where the panel lives | Build it as |
|---|---|
| Classroom or lab bench, 24 V DC, supervised | Open frame, guard passing the 12 mm probe |
| Clean indoor space, line voltage present | Frame with shrouded line side, or a Type 1 box |
| Indoor with dripping water or condensation | Type 2 |
| Indoor shop floor, dust and lint | Type 12 |
| Indoor oil or coolant spray | Type 13 |
| Washdown, food plant, salt or chemicals | Type 4X, 316L for chlorides |
| Outdoors in rain and sun | Type 4X (Type 3R is the rain minimum) |
| Submerged or buried in wet ground | Type 6P |
ANSI/NEMA 250-2020 puts Types 1, 2, 5, 12, 12K and 13 indoors and the 3, 4 and 6 families out in weather, hose water and immersion. Type 2 is the middle step people forget: indoor protection against dripping and light splashing, which is exactly what a ceiling that drips needs. NEMA Type 2 rating explained
What to put on the drawing or the order
For the frame route, write three lines on the drawing. Guard openings below 12 mm — 3/8 in [9.5 mm] cloth blocks the probe outright — or live parts at least 100 mm behind any larger opening. Line-voltage terminals on finger-safe blocks or in a closed side box. And a label that reads indoor, dry, supervised use, because that is the envelope the build honestly has.
For the rated route, start from your panel and pick the box. Our stainless wall-mount line spans 6 x 4 x 4 in to 60 x 36 x 16 in outside (H x W x D), in 304 stainless for indoor washdown, food and beverage and most outdoor sites, and 316L for salt air, brine and chemical areas. Every cutout comes cut to your drawing from one piece, and delivery is 10 business days from your approval of the drawing. The enclosure selector shortlists by environment and inside size; the stainless size finder filters the whole line; and the custom builder takes your exact width, height, depth and cutouts from a single piece. If the box is new territory, the sizing guide walks the heat load and the wire-bending space before you commit. the enclosure selector the stainless size finder the custom enclosure builder the enclosure sizing guide
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 |
|---|---|---|---|
| 20 × 16 × 8 in | 316L stainless | 20 x 16 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 |
| 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
Can a shop-built open frame carry a NEMA rating?
Not on paper. ANSI/NEMA 250 defines the types, and the manufacturer rates its own tested designs; NEMA itself tests and certifies nothing. A guarded frame behaves like IP2X: a jointed 12 mm probe stays off live parts, but nothing in the build is tested against dust or water. Once dust, hose water or weather join the picture, the panel moves into a Type 12, 4X or 6P box.
What mesh opening keeps the test finger off live parts?
Any clear opening below 12 mm blocks the probe outright, so 3/8 in [9.5 mm] hardware cloth works at any terminal depth. True 1/2 in [12.7 mm] cloth admits the probe: mount live parts at least 100 mm [4 in] behind it, past the probe's 80 mm length and its joint sweep. Count clear openings, not wire pitch.
Does IP20 cover dust?
The 2 means a jointed finger cannot reach live parts; the 0 means no water protection at all. Dust enters the code only at IP5X, which is dust-protected, and IP6X, which is dust-tight. An IP20 PLC on an open frame is therefore finger-safe and nothing more, and a dusty room still calls for a Type 12 box or better.
What rating does a dusty indoor shop floor need?
Type 12, an indoor type covering dust, lint and dripping non-corrosive liquids — the standard step up from a frame on a plant floor. Oil and coolant spray call for Type 13. Washdown and hose cleaning call for Type 4 or 4X, with 316L stainless where salt or chlorides are present.
Can I build the panel open now and box it later?
Yes, and it is the usual path. Keep the backplate, DIN rail and wiring, then mount the same panel in a custom stainless box: outside sizes run from 6 x 4 x 4 in to 60 x 36 x 16 in, every cutout comes cut to your drawing, and delivery is 10 business days from your approval of the drawing. The rating then belongs to the box as the manufacturer's rating, not UL listed.
