Mount the computer inside the box, not behind the glass. A fanless mini PC and an IP66-front capacitive touch panel, built into a 316L stainless wall-mount enclosure, outlast a third purpose-built washdown panel PC in a tunnel car wash. The housing arrives manufacturer-rated NEMA 4X-type / IP66, not UL listed, and each part that wears out swaps on its own. The assembly rating ends up wherever the weakest seal sits, so the display front and the two cord glands deserve the same attention as the box itself. Material decides the rest: a wet tunnel keeps chloride-bearing cleaner film on every surface, 304 pits at room temperature in exactly those films and crevices, and 316L is the grade for that duty. The worked example below sizes the box and its heat; the closing table lists the order line by line.
What a tunnel wash does to a panel PC
A tunnel wash attacks a panel three ways, and each picks its own failure.
Water sits on everything. Between cycles the air at wash height runs near saturation, so steel a few degrees under ambient fogs and drips long after the last car. Cleaner mist carries chlorides, and when the film dries the salts concentrate on the surface. On 304 stainless, that film pits the metal at room temperature; the first pits start under deposits and in the crevice under a door gasket, where the film sits longest. Why wet-dry cycling rusts 316L before you blame the grade follows that chemistry step by step.
Heat adds the serious one. From about 60 C (140 F) up, chloride stress-corrosion cracking threatens 304 and 316L alike, and the molybdenum in 316L raises pitting resistance without moving that threshold. A hot computer bolted behind a display can hold a skin near that line; the worked example below keeps this build under 40 C, more than 20 K clear of it.
Fans are the third way in. A fan-cooled computer pulls tunnel air through its own chassis and lays the mist onto its boards. A fanless PC sealed in a gasketed box has no inlet at all, which is the quiet argument for the box route before corrosion even enters. The washdown touchscreen guide covers the display side of the same build.
The rating the assembly needs
Put NEMA 4X / IP66 on the drawing, then hold it on every part.
Type 4X under NEMA 250 is a watertight Type 4 build with a corrosion element added. UL 50E gives Type 4X enclosures another 200 hours of salt spray alongside an AISI 304 test specimen, in Table 5-1D. Keep the NEMA Type on a US drawing next to the IP code; NEC 110.28 states that IP ratings are not a substitute for enclosure Type ratings.
The IP half comes from IEC 60529. First digit 6 is dust-tight. Second digit 5 is a jet test: a 6.3 mm nozzle at 12.5 L/min. Second digit 6 is powerful jets: a 12.5 mm nozzle at 100 L/min, the closer match when someone hoses the wall down or the arch oversprays your panel. The same IP65-versus-IP66 call faces every device mounted in a wash tunnel; a companion engineering page weighs it for tunnel sensors in IP65 vs IP66 selection for cleaning tunnels.
Then defend the number across four parts: the housing, the display front seal, the cord glands and the door pass-through. The assembly carries the lowest rating among them. A shop-drilled hole erases it in seconds, and what a panel keeps after you cut it and mount devices shows exactly how. Order every opening from the factory and the chain holds; the cutouts, glands and HMI windows guide lists what belongs on the drawing.
Why 316L wins this wall
Choose the grade by what sits on the surface. 304 handles splash and rain; a chloride film that sits and dries is another duty, and it pits 304 at room temperature in deposits and gasket crevices. The 2-3% molybdenum in 316L raises pitting and crevice resistance, which is the failure mode this film drives. The 304 vs 316L guide carries the full comparison, and tea-staining in a washdown plant shows what early attack looks like while it is still cosmetic.
Above 60 C (140 F) wall temperature the argument ends, because chloride stress-corrosion cracking threatens both grades and no chemistry choice fixes it. That is a heat argument, and this build wins it by staying cool: a 15 W-class fanless PC cannot drive a 1.49 m² box anywhere near that line. Keep the big heat loads out of a chloride-washed box and the grade choice becomes permanent.
Size and heat, worked through
Size the box as a heatsink before you order anything. Treat the numbers here as a worked example: swap in your PC's dissipation figure and the rises scale with it.
Assume a fanless mini PC dissipating 15 W, a 24 x 30 x 8 in (H x W x D) 316L wall-mount enclosure, and 30 C tunnel air. Wetted wall area is 2 x (24 x 30 + 24 x 8 + 30 x 8) = 2,304 in², about 1.49 m². Stainless transfers k = 3.7 W/m²K, so the box sheds 3.7 x 1.49 = 5.5 W per kelvin of inside-to-outside difference. The PC alone lifts the inside air 15 / 5.5 = 2.7 K, to about 33 C, with the wall skin between the two at roughly 31 C.
Condensation, not processor heat, sets the next number. A sealed box in saturated air fogs from the inside whenever its skin runs under the dew point, so the fix is an anti-condensation heater on a hygrostat. Holding the inside air 5 K above the tunnel costs 1.49 x 5 x 3.7 = 28 W, which a 30 W heater covers.
Worst case, heater and PC run together at 45 W. That is 45 / 5.5 = 8.2 K of rise, about 38 C at a 30 C tunnel. It stays under the 40 C (104 F) ambient most electronics carry unless a datasheet allows more. Switch the heater circuit out above 31 C ambient, and the PC-only rise of 2.7 K keeps the box under 40 C up to a 37 C tunnel. Double the PC to 30 W and the PC-only rise doubles to 5.5 K, still fine on its own; the combined 60 W case reaches 10.9 K and breaches 40 C at a 30 C tunnel, so a 30 W PC wants the next box size up or a heater that only runs on cold, humid hours.
The skin stays 20 K or more below the 60 C chloride line in every 15 W case. Assemble the box dry, drop in a fresh desiccant pouch at each service visit, and the sizing guide covers the electrical side: bending space at terminals, duct fill at the 50% the duct tables allow, and spare rail for the next revision. Wire the supply and heater dead: lock out the tunnel feeder and confirm absence of voltage first.
Ports, display and the door
The port area is where one-piece panel PCs leak, and this layout removes it.
A touch monitor's rating covers its glass and bezel; its rear connectors carry their own seals or nothing at all. Here the mini PC sits on the backplate inside the sealed box, so HDMI, USB and power never cross an outside wall. Only two cords enter from the tunnel, the 24 V DC feed and the Ethernet lead, each through a cord gland sized to its outside diameter. An M20 gland typically clamps a 5-10 mm cord and an M25 roughly 9-14 mm; the gland's own datasheet range is the deciding figure. Clamped on the right cord and torqued, the gland carries its IP rating into the assembly. A round RJ45 panel feedthrough with silicone seals, sold at IP65, is the common alternative for the network lead; it caps that entry, and with it the assembly, at IP65.
The display seals where it should. Order the door opening factory-cut to the touch panel's outline, seat its gasket on the door, and its front rating becomes the assembly's: IP66 front, IP66 assembly; IP65 front, IP65 assembly. The display lead crosses from door to body at the hinge side, so put a sealed pass-through on the cutout drawing; mounting an operator panel in a cabinet door walks that crossing in detail. Two pages cover the day a port must move outside the box: sealed panel-mount HDMI ports and waterproof panel-mount connectors.
What to put on the order
Send the touch panel outline, the hinge-side pass-through and the two gland centres with the order, and the box arrives cut and gasketed.
| Line | Spec to send |
|---|---|
| Housing | 24 x 30 x 8 in (H x W x D) 316L wall-mount enclosure, manufacturer-rated NEMA 4X-type / IP66, not UL listed, set up for a mini PC |
| Door cutout | Factory cut to the touch panel outline; this door takes panels up to 23.8 in, so a 21.5 in capacitive panel fits with margin |
| Pass-through | Sealed display-lead pass-through, hinge side |
| Cable entries | Two cord glands, M20 for 5-10 mm cords, IP66-rated at the clamped size |
| PC | Fanless mini PC, 15 W class, datasheet ambient 40 C or better |
| Condensation | 30 W anti-condensation heater with hygrostat, switched out above 31 C ambient |
| Power | DIN-rail 24 V DC supply on the backplate, fused at its rating |
| Turnaround | Delivered in 10 business days from drawing approval |
Decide by what actually hits the wall:
- Mist, splash and saturated air, with no hose aimed at the panel: this build as listed, and spec the IP66 front anyway as margin.
- Hose-down of the wall or overspray from the arch: keep the IP66 front, the Type 4X housing and IP66 glands; the 100 L/min test exists for that hose.
- Direct high-pressure or steam cleaning aimed at the panel: neither IP66 nor a Type 4X housing claims that duty, so put a purpose-built high-pressure washdown unit in that spot.
Two catalog pages anchor the ends of that decision. In the tunnel, the 24 x 30 x 8 in 316L wall-mount enclosure is the box in the worked example. On the dry side of the wall — office, electrical room — the 21.5 in 304 HMI housing carries an IP65-type front seal with the display installed and skips the chloride argument entirely. Browse from the 316L wall-mount range or the HMI housing range and the built box arrives in 10 business days.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 24 × 30 × 8 in | 316L stainless | 24 x 30 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 21.5" HMI enclosure | 304 stainless | 14.69 x 23.03 x 3.86 in | IP65-type front seal with the display installed, manufacturer rated; not UL listed |
Questions
Can I keep the PC in a dry room and run one HDMI cable to the tunnel?
You can, and it protects the computer, but every signal crossing the wall becomes another part that caps the rating. An HDMI run of tens of metres needs active extenders at both ends, each with its own sealed entry; a single IP65 RJ45 feedthrough alone caps the whole assembly at IP65. With the PC inside the box, the only crossings are two cord glands, and the HDMI lead never leaves the sealed volume.
Is IP65 enough for a car wash station?
For a queue station above the splash line and out of the arch spray, yes: the IP65 test is a 6.3 mm nozzle at 12.5 L/min, and mist never reproduces it. Staff hosing the wall or arch overspray is the IP66 case, a 12.5 mm nozzle at 100 L/min. Mount the station about 1.5 m up, near eye height, on the wall that only sees mist and the front seal rarely works hard.
Will a 316L enclosure still show rust in a wash tunnel?
It can tea-stain where cleaner film sits and dries, especially in gasket crevices. Rinse the box with fresh water at service intervals, wipe the gasket seat, and re-passivate any weld or scratch mark. Keep the skin under 60 C (140 F); past that, chloride stress-corrosion cracking threatens both 304 and 316L, and no wash chemistry fixes it.
What rating does the finished assembly carry?
The lowest rated part in the chain. The 316L housings are manufacturer-rated NEMA 4X-type / IP66, not UL listed; an IP66-front touch panel holds the assembly at IP66, an IP65 front caps it at IP65, and each gland carries its own rating only at the cord size it clamps. Put the weakest part's rating on the drawing and call that the assembly rating.
How fast does a custom-cut 316L box arrive?
Delivered in 10 business days, counted from your approval of the drawing for custom cutout work. The drawing carries four things the factory needs: the touch panel outline, the hinge-side pass-through, the two gland centres and where the mini PC sits. With those sent, the box arrives cut, gasketed and ready to wire.
Is a purpose-built stainless washdown panel PC the better buy?
It is when the panel sits in the direct spray path or under high-pressure washdown, duties no IP66 front claims. For a queue-selection screen outside the spray, the box route keeps the two wear parts separate: the display dies, you swap a touch panel; the PC ages out, you swap a 15 W-class mini PC; the sealed enclosure stays.
