Yes — when the cabinet itself carries the rating, the wiring inside can be open: bare conductors dressed from terminal block to terminal block, no conduit, no covers on interior boxes. A shell rated NEMA 3R, 4 or 4X is the weather barrier for everything mounted inside it, and an inner mounting panel inherits that protection. Conduit reappears where the conductors leave the cabinet, through a gasketed hub sized to each cable. Two rule books meet at the door: the enclosure rating governs the outside wall, and the panel wiring rules govern what you do inside it.
The shell is the weather barrier
The enclosure Type number describes the wall of the box, not the wiring method. Type 3R is built for rain, sleet and snow. Type 4 adds hose-directed water, the washdown stream. Type 4X keeps that sealing and adds corrosion resistance, which NEMA 250 proves with 200 hours of salt spray run alongside an AISI 304 stainless specimen. NEMA publishes these definitions and does not test, certify or endorse enclosures. Manufacturers rate their own shells: ours are rated NEMA 4X / IP66 by the manufacturer, not UL listed.
In US installations, NEC 110.28 keeps the IP code on its own scale, separate from the enclosure type; the NEC Table 110.28 article shows where the code lists the types. What the tests cover decides the whole question. The hose test for Type 4, the powerful jets of IEC 60529's IPX6 — a 12.5 mm nozzle at 100 L/min — and the 200 hour salt spray all finish with the inside dry. None of them looks at how you route a harness, how full the wire duct runs, or which terminals sit behind the door.
The rating buys a dry backplate; the wiring plan is panel design. That is why bare conductors are the normal case inside, and why an open-frame device works in a rated shell — the open frame vs rated enclosure article takes that pair apart.
Why the wiring inside can be open
The NEC's wiring-method rules govern conductors on their way to the cabinet: from source to wall, a Chapter 3 wiring method — raceway, cable or cord — carries them. Once a conductor passes through its hub, it is inside the equipment and other rules apply. NEC 409.2 defines an industrial control panel: an assembly of two or more power circuit components, control circuit components, or both. UL 508A is the standard for listing one.
The panel standard's internal wiring rules are about the conductors themselves. They call for copper wiring, power circuit conductors at 14 AWG or larger, and control wiring down to 18 AWG where the circuit is protected at 20 A or less. Nothing in that scheme asks for conduit between a terminal block and a drive terminal.
Open does not mean abandoned. Dress your harnesses in wiring duct or as loomed bundles on the backplate, and plan your layout around the fill cap the duct makers publish: 50% of the interior cross-section, citing NFPA 79-2012 section 13.5.2. Past half full, the air gaps between round cables are gone and the slots will not close. The backplate and DIN rail layout guide shows how that cap shapes a panel layout.
When an interior junction box earns a cover
Inside the shell, weather never reaches a junction box, so a cover buys no rating. It buys three practical things. It separates 480 V power wiring from 120 V or 24 V control wiring, so a hand reaching for a control terminal cannot touch a power terminal. It keeps a dropped screw or a slipped driver from bridging live parts during troubleshooting. It stops conductor chafe where a bundle crosses a sharp edge. Match the hardware to the job: a screwed cover on the power side, a hinged one where you get in weekly.
Open terminals are live when the door swings: treat the open cabinet as energized and verify absence of voltage before you reach inside.
Open wiring troughs and gutters bolted to the backplate work the same way: part of the panel, dry behind the door gasket, in need of no covers or drains of their own. The wiring trough to panel connection article carries the rating across that joint, and the junction box vs terminal enclosure article draws the line between a real junction box and a plain terminal enclosure.
Entries and drains decide the rating
Every conductor crosses the shell through a fitting, and the fitting is where the rating is kept or lost. The weakest part sets the assembly rating: one vent, hub or gland rated below the shell pulls the whole box down to its number. Order a gasketed hub for every entry, sized to the cable's outside diameter, so the seal grips the sheath. That contact is the whole seal, as this page on why a gland seal must contact the cable outer sheath explains.
Bring conductors in from the bottom where you can; the bottom conduit entry article shows why falling water loses that race. Field-drilled holes keep a Type 4X rating when they are deburred and closed with a matching gasketed fitting — the field-drilled conduit entries article walks that job. A bare stainless backplate inherits the shell's rating as installed; what moves the number is each device and fitting you mount, which the rating after mounting devices article counts up.
Drainage belongs to the 3R design. NEC 314.15 allows approved drain openings of 3 mm (1/8 in) to 6 mm (1/4 in) in boxes listed for damp or wet locations, and a rain-exposed 3R shell takes one at its lowest point; the 3R vs 4 guide separates the two designs. A sealed Type 4 shell replaces the drain with gaskets and gasketed hubs, so plan entries instead of holes. NEC 409.110 also requires the enclosure type number on a listed panel — one more reason the shell's Type is the number you specify.
The space the cabinet owes the worker
You still owe the worker room, and the NEC sets the numbers. NEC 110.26(A) requires clear working space in front of equipment likely to be serviced while energized. For 0-150 V to ground in Condition 1, that means at least 3 ft (900 mm) deep, at least 30 in wide or the equipment width, and room for the door to swing 90°. NEC 240.24(A) puts the center of the grip of the highest operating handle, in its highest position, at most 2.0 m (6 ft 7 in) above the floor. Large feeders get the wire-bending room NEC 312.6 sets at terminals. The enclosure mounting guide and the enclosure sizing guide carry both.
Worked example: a lift-station control cabinet, custom 304 stainless, 60 in high × 36 in wide × 16 in deep, manufacturer-rated Type 4X, on a 12 in plinth, controls at 120 V.
- Working space. 120 V to ground sits in the 0-150 V band, so NEC 110.26(A) asks 3 ft (36 in) of depth, and the width is the larger of 30 in and the 36 in equipment width: 36 in. Keep a 36 × 36 in clear patch in front, door swinging 90°.
- Handle height. Breaker handle centers sit 55 in above the cabinet base: 55 + 12 = 67 in, which is 12 in under the 79 in (6 ft 7 in) ceiling. The same row on a 24 in stand lands at 55 + 24 = 79 in — legal, with nothing to spare — so every inch of stand has to come off the row height.
- Result. The open-wiring plan costs floor space, not conduit: give the cabinet its 36 × 36 in patch and hold the handle line at or below 79 in.
What to put on the order
Specify the shell to carry the whole rating, then wire it open. The numbers that govern the build:
| Duty | What does the work | Number to hold |
|---|---|---|
| Rain, sleet, snow | Type 3R shell | 3-6 mm (1/8-1/4 in) drain at the low point |
| Washdown or hose | Type 4 shell | Gasketed hubs, entries from below, no drain |
| Salt air, chemical washdown | Type 4X shell in 316L | 200 h salt spray behind the rating |
| Conductor size inside | UL 508A panel wiring | 14 AWG power minimum; 18 AWG control at 20 A protection or less |
| Duct fill | NFPA 79-2012 section 13.5.2 practice | 50% of interior cross-section |
| Working space | NEC 110.26(A) | 3 ft deep, 30 in wide, door at 90° |
| Handle height | NEC 240.24(A) | 2.0 m (6 ft 7 in) maximum |
Order the shell as a custom build when the plan outgrows a catalog box: 304 stainless for most outdoor sites, 316L for salt air, brine and chemical washdown; your width, height and depth; a removable inner panel; bottom cutouts drawn to the hub count; a hinged gasketed door. We build those from one piece and deliver in 10 business days, counted from your approval of the drawing. The shells are manufacturer-rated, not UL listed; where a project demands a listed panel, the unlisted enclosure article sets out the route panel builders take.
Decision by site:
- Rain and snow, never washed: Type 3R shell, open wiring inside, one 3-6 mm drain at the low point.
- Washdown or hose area: Type 4 shell, every entry gasketed and from below, no drain.
- Salt air, brine or sanitizer washdown: Type 4X in 316L — the same sealing with a corrosion margin.
- Standing water or submersion: send the depth, duration and fluid with the inquiry, and the Type 6P design is confirmed against those conditions before steel is cut.
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 |
|---|---|---|---|
| 60 × 36 × 16 in | 304 stainless | 60 x 36 x 16 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 48 × 36 × 16 in | 304 stainless | 48 x 36 x 16 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 60 × 36 × 12 in | 304 stainless | 60 x 36 x 12 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How much slack do I leave on conductors inside the cabinet?
At every connection point, leave each conductor long enough to extend at least 3 in past the opening it came through when that opening is under 8 in in any dimension. A 12-conductor control harness needs 36 in of extra copper across the bundle, so plan the loop before you cut the wires to length.
Does the inner mounting panel need to be bonded?
Yes. NEC 250.96(A) requires metal parts intended to serve as equipment grounding conductors, including enclosures, to be bonded together so they can safely conduct any fault current likely to be imposed on them. Bolt the stainless panel to the enclosure's ground stud through a toothed washer, and clear paint or scale from the contact faces as NEC 250.12 directs. Stainless on stainless bonds cleanly with a scraped bright point under each ground screw.
Can I make splices inside the cabinet instead of in a box?
Yes, within the limits that govern cabinets. NEC 312.8 limits how much of an enclosure holding switches or overcurrent devices may be filled with conductors, splices and taps, so keep splices in the duct or gutter area rather than packed behind breakers. Make each splice in a listed pressure connector, insulate it, and the open-wiring plan works with no interior j-box at all.
Can a plastic wiring trough run inside a Type 4X shell?
Yes, when the trough is flame retardant: NFPA 79-2015 section 13.3.1 permits nonmetallic duct inside enclosures only when it passes the IEC 60332-1 flame test. The trough stays dry because the gasketed door and gasketed hubs keep water out, so it needs no cover, gasket or drain of its own. Its rating job is mechanical, not environmental.
