Plasma table computer enclosure: dust protection that works

Short answer: seal the computer inside a gasketed 304 stainless enclosure rated NEMA 4X / IP66 by the manufacturer, and keep the heat load low enough that the stainless walls do the cooling. Walls pass about 3.7 W per square metre per degree of rise, so a 20 W fanless mini PC in a 16 x 16 x 8 in box runs about 8 C above shop air — 38 C inside a 30 C shop, under the 40 C limit most electronics carry. A desktop tower at 60 to 150 W breaks that math and forces a filtered fan, which drops the assembly to IP54. The sections below walk the dust, the rating, the material, the size and the sealing, and end with the order spec.

What is actually in the air around a plasma table?

Two streams of pollution, not one: fine metallic dust thrown off the kerf, and smoke from molten metal that peaks while you pierce thick plate or cut galvanized stock — a water table settles most of the dust, and the smoke still travels.

The dust matters more than its quantity suggests because it conducts. Wood dust blankets a board and traps heat, which is the failure mode behind most dust-resistant switch enclosure decisions; metallic dust does that and also bridges live terminals once it picks up a little moisture. Low-voltage logic and 24 V DC supplies tolerate it badly.

Your computer's own fans are the worst offender. An unsealed desktop pulls shop air through its case around the clock, which is why a month of cutting leaves a gray film on every board inside it. A sealed box with no airflow collects almost nothing, and a filtered box collects only what the filter misses.

Cutting galvanized stock makes zinc oxide fume, which is a lung hazard before it is an electronics problem — extraction at the table protects you and every filter downstream. That one sentence is the whole safety note.

What enclosure rating does the computer need?

Order a gasketed enclosure rated NEMA 4X / IP66 by the manufacturer — ours are marked that way and not UL listed — because IEC 60529's first digit 6 means dust-tight, and dust-tight is the whole game at a plasma table.

The digits say exactly what you are buying. IEC 60529's first digit 6 allows no dust ingress at all in its powder test; digit 5, dust-protected, allows a limited, harmless deposit — which is the honest description of a filtered box. Second digit 6 shrugs off powerful jets, a 12.5 mm nozzle at 100 L/min, while digit 4 covers only splashing water. A rag and a splash test nothing here, but one day someone will hose the station down.

In US installations, NEC 110.28 says an IP code is never a substitute for an enclosure type rating, so if the spec or the inspector names a type, the marking on the box must say 4X. NEMA itself tests nothing: the type marking is the manufacturer's declaration, and ours says NEMA 4X / IP66 by the manufacturer, not UL listed.

The rating you keep is the rating of the weakest part. A cord grip, a connector or a fan at IP54 drags a 4X box down to IP54 the moment you fit it — what a fan costs a NEMA 4X rating covers that trade, and what NEMA rating a panel keeps after you cut it and mount devices covers the holes. The IP rating chart prints the digits side by side.

Sealed box or filtered fan: which one handles the heat?

Run the wall math first: stainless passes about 3.7 W per square metre per kelvin of rise (this site's reference value), so watts divided by 3.7 times wall area gives your rise — 20 W into a 16 x 16 x 8 in box is about 8 C.

Worked example, a mini-PC station:

• Enclosure 16 x 16 x 8 in [406 x 406 x 203 mm] outside = 0.41 x 0.41 x 0.20 m
• Wall area: 2 x (0.41 x 0.41) + 4 x (0.41 x 0.20) = 0.66 m²
• Heat passed per degree: 3.7 W/m²K x 0.66 m² = 2.4 W/K
• Rise: 20 W ÷ 2.4 W/K = 8.2 C

At 30 C shop air the box sits at 38 C, under the 40 C ambient rating that boards and power supplies carry unless their datasheets say more. At 35 C it sits at 43 C and fails, so the sealed answer holds while the shop stays under about 32 C — true for most shops, false for a south-wall shop in August.

Typical heat to plan for, from nameplate draws:

The decision falls straight out of the sum:

In the fan case, size airflow as about 3 m³/h per watt per 10 C of rise: 3 x watts ÷ rise in C. A 100 W desktop plus a 30 W monitor at a 10 C rise needs 3 x 130 ÷ 10 = 39 m³/h [23 CFM]. Order a fan with roughly twice that free-air flow, because the filter and the finger guard spend the difference on pressure drop. The enclosure fan airflow calculation works it with the temperature margin explicit.

Fit the fan on the intake side, blowing in through its filter, with a second filtered opening as exhaust: the box then runs a few tens of pascals above room pressure and every seam leaks outward. A desktop is fine inside that cabinet, because its internal fans only see filtered air. Filter-fan assemblies carry IP54 as a class, so that is the enclosure you own from that day. Check the medium monthly, and shorten to two weeks if two weeks of cutting loads it. A thermostat starting the fan at 30 C saves the filter overnight — see thermostat control for an enclosure fan — and in a plasma shop you want it running whenever the torch is.

Why 304 stainless for a machine-shop enclosure?

Because sparks and grinding swarf, not rain, are the indoor hazard: plasma spark spray and grinder sparks burn paint and char plastic, while 304 stainless takes the hits, wipes clean of the gray film, and keeps the gasket seat flat.

Burnt paint under a door flange is a leak path disguised as cosmetics: the steel rusts, the surface lifts, and the gasket stops sealing long before anyone calls it a failure. Plastic enclosures take spark strikes as melted pits. Stainless shrugs both off, and the stainless size finder lists every wall-mount box in 304 and 316L by outside size.

Order 316L when the shop sits on the coast or the floor crew mops with chlorinated sanitizer: 304 can pit under chloride deposits even at room temperature, and a pit under a gasket is a leak. For an inland machine shop with ordinary cleaning chemicals, 304 is the right grade and the right spend.

How big does the enclosure need to be?

Plan the mounting panel, not the PC's footprint: a mini-PC station with power supply, terminals and a small UPS fits a 16 x 16 x 8 in [406 x 406 x 203 mm] enclosure, with about 20 percent of the panel left spare.

Depth is the first dimension to check, because the deepest item sets it: a mini PC on a bracket with connectors facing down wants 8 in, and a UPS on the panel wants more. Height and width come from laying the parts out — component layout inside a sealed enclosure shows how spreading hot parts against the walls buys cooling area you would otherwise pay for in size.

Outside sizes in the line run from 6 x 4 x 4 in to 60 x 36 x 16 in (H x W x D), and a custom box takes your exact three dimensions and every cutout. Wall area is the cooling budget: doubling the surface doubles the watts a sealed box sheds at the same rise. The enclosure selector filters by inside height and width, so you can start from the panel and work outward.

How do you mount it and seal the cables?

Wall-mount the enclosure out of the table's downdraft and above mist height, and bring every cable in through cord grips in the bottom wall, one cable per grip, sized to the cable's outside diameter.

Bottom entry is the whole trick: gravity keeps dust and mist out of a gland that weeps. The cutouts, glands and HMI windows guide matches knockout sizes to fitting dimensions, and two cables share one gland only with a split seal rated for the pair — two cables through one cable gland says when that holds. If the station must roll, bolt the enclosure feet to a stand instead of the wall; the gasket does not care what is behind it.

Wipe the door gasket at the monthly filter check: metal dust on a gasket holds moisture against the stainless and works like wet sand. For the display, a panel PC in a stainless HMI housing replaces monitor, arm and keyboard shelf with one sealed unit — an IMD 15 in panel PC housing carries an IP65-type front seal with the display installed, and display sizes run from 7 to 23.8 in. Carry a wireless keyboard to the torch, and leave nothing with a fan or a slot outside a sealed box.

What should the order say?

Write it in eight lines — grade, rating, size, heat path, cutouts, mounting, display, lead time — and a custom stainless enclosure is delivered in 10 business days, counted from your approval of the drawing.

The decision, by what sits on your panel:

• Mini PC or panel PC at 25 W and under: sealed 4X box at 16 x 16 x 8 in, cord grips only, done.
• Panel PC plus UPS at 25-45 W: sealed 4X box at 24 x 24 x 10 in, still no openings beyond the glands.
• Desktop and monitor above 60 W: filtered fan at IP54 with positive pressure and monthly filter checks, or move the desktop out of the shop air and keep a sealed box at the table for the interface.
• Coastal or bleach-washed shop: the same two boxes, ordered in 316L.

Enclosures in this article

Questions