Put the drive, its 24 V supply and the relays in a stainless box rated NEMA 4X / IP66 by the manufacturer whenever the room sees coolant mist, chips or a hose. Keep the same kit in a Type 12 steel box when the room stays dry. Drives turn 2-4 % of their rated output into heat, and a sealed 20 x 16 x 8 in stainless box carrying 100 W runs about 35 C over the room. Most drives top out at 40 C inside, so the heat decides the size as much as the room decides the rating. The room picks the type, the chlorides pick the grade, and the watts pick the square inches; all three numbers follow, with one worked example and the order sheet at the end.
The room decides the rating
Near a machine tool, the enemies are coolant mist, chips and the wash rag. Mist is the worst of them: it rides every vent slot and plates the drive boards within a season. Dry electrical rooms are kinder, and a lighter rating is enough there.
| Where the box sits | What reaches the electronics | Rating to order |
|---|---|---|
| Clean, dry electrical room, inside a closed console | Fingers, occasional dust | Type 1, or Type 12 in a dusty room |
| Shop floor with dust, no coolant | Dust, lint, a dripping line overhead | Type 12 |
| Machining cell with coolant mist and chips | Oil mist, chips, solvents on a rag | NEMA 4X / IP66, 304 stainless |
| Washdown bay, food plant, outdoor wall | Hose jets, cleaners, rain and sun | NEMA 4X / IP66, 316L stainless |
A vented computer case belongs on the first row and nowhere else. Its slots pass everything the bottom two rows describe, and it carries no enclosure type at all.
What the rating on the door means
Type 12 is the indoor rating for dust, dirt and dripping liquids. Type 4X adds hose-directed water and corrosion resistance, indoors or out. The IP66 half is the international test: IEC 60529 sprays the enclosure with powerful jets from a 12.5 mm nozzle at 100 L/min, and no water may reach the live parts during or after it. Our enclosures carry both markings and are rated NEMA 4X / IP66 by the manufacturer; they are not UL listed. A UL listed enclosure has been evaluated by UL to UL 50E, and what UL 50E listing covers is worth a read before your spec sheet calls for one.
Two rules finish the picture. NEC 110.28 keeps an IP code from standing in for a type rating on US installations, so order the type from the table above and let the IP66 marking ride along on the nameplate. And the finished cabinet takes the rating of its weakest part: one IP54 filter on a 4X door makes an IP54 cabinet, which matters in the cooling section below.
304 or 316L for the shell
304 stainless covers indoor machining cells, food and beverage washdown and most outdoor walls. Move up to 316L when salt air, brine or chloride-bearing cleaners reach the box, and for pharma and chemical areas. Two chloride facts drive the choice: 304 can pit at room temperature under a deposit left in a gasket crevice, and about 60 C is the chloride stress-corrosion threshold for both grades. The molybdenum in 316L buys pitting and crevice resistance, and it does not move that threshold. The full comparison lives in the 304 vs 316L guide; for the machining cell in this article, 304 with a #4 brushed finish is the right order.
Count the watts before the square inches
A sealed box sheds heat through its walls, and stainless walls move about 3.7 W per square metre per degree of rise (k = 3.7 W/m²K). The working formula is simple: temperature rise = heat load ÷ (k × wall area). Count all six faces, because the stand-off feet hold the box off the wall and the back still convects; 1 m² is 1,550 in². Your allowed rise is the drive's 40 C inside limit minus the hottest room temperature, so a 25 C room gives you 15 C to spend and a 35 C summer room gives you 5 C.
| Heat source | Typical heat at full load |
|---|---|
| VFD, 2-4 % of rated output (96-98 % efficient) | 5 hp [3.7 kW] drive: 75-150 W |
| 24 V supply at 90 % efficiency | 13 W lost per 120 W of output |
| Relays, contactor coils, terminals | 5-15 W in a small panel |
Take the drive's own watts from its datasheet once you have it; the percentages are for the first pass. This table turns watts into wall at a 15 C allowed rise:
| Heat inside the box | Wall area needed | One box that clears it (H x W x D) |
|---|---|---|
| 25 W | 700 in² [0.45 m²] | 16 x 12 x 8 in |
| 50 W | 1,400 in² [0.90 m²] | 24 x 20 x 8 in |
| 100 W | 2,800 in² [1.80 m²] | 36 x 24 x 10 in |
| 150 W | 4,200 in² [2.70 m²] | 48 x 30 x 12 in |
Pick the nearest stock size in the stainless size finder, or have the exact size built custom; the math does not care which route you take.
Sizing the box: a 5 hp drive, its supply and relays at 25 C
Inputs. A 5 hp [3.7 kW] drive at full load, the classic single-axis machine-tool fit; drive makers publish a 2-4 % loss band, so take 3 % until the datasheet lands. A 24 V supply delivering 120 W at 90 % efficiency. Ten watts of relays, coils and terminals for a small panel. A 25 C worst-case room, a 40 C drive limit and k = 3.7 W/m²K for a stainless wall.
Rule in words. Rise equals watts divided by wall coefficient times area; turn it around and area equals watts divided by coefficient times allowed rise.
Arithmetic.
- Drive: 3,700 W × 0.03 = 111 W
- Supply: 120 W ÷ 0.90 = 133 W drawn, so 133 − 120 = 13 W lost
- Panel: 10 W
- Total: 111 + 13 + 10 = 134 W
- Allowed rise: 40 C − 25 C = 15 C
- Area needed: 134 W ÷ (3.7 W/m²K × 15 K) = 134 ÷ 55.5 = 2.41 m² [3,740 in²]
Candidate check. A 36 x 24 x 10 in box gives 2(36×24) + 2(36×10) + 2(24×10) = 2,928 in² [1.89 m²]. Its rise is 134 ÷ (3.7 × 1.89) = 19 C, so the inside reaches 44 C. Rejected. A 48 x 30 x 12 in box gives 2(48×30) + 2(48×12) + 2(30×12) = 4,752 in² [3.07 m²]. Its rise is 134 ÷ (3.7 × 3.07) = 12 C, so the inside sits at 37 C with 3 C in hand.
Decision. Order roughly 4,700 in² [3.0 m²] of stainless wall for this load in a 25 C room. Then run the summer check: at 35 C ambient the allowed rise falls to 5 C and the area wanted becomes 134 ÷ (3.7 × 5) = 7.2 m². Even a 60 x 36 x 16 in box, the largest stock size at 4.8 m², would land at 43 C inside. In a 35 C room that same box holds only about 90 W sealed, so past that, stop sizing and start cooling.
Cooling that keeps the seal
Below about 50 W, sealed stainless usually wins on simplicity. From 50 W to 150 W in a cool room, buy wall: every extra square metre of stainless sheds 55 W at a 15 C rise. Past 150 W, or in any 35 C room, fit cooling and choose it by the room:
- Dry Type 12 room: a fan-filter kit is the cheap fix, and the cabinet honestly takes the filter's rating, typically IP54 as the makers mark them. The room already tolerates that. -Near coolant, keeping 4X: cool with a closed loop. An air-to-air heat exchanger moves heat through a sealed core while the inside air never meets the mist, and an enclosure air conditioner does the same with more muscle. Both leave the type intact.
For a single drive's step-by-step numbers, the drive-by-drive sizing article works a full example, and the hot-room cooling options article compares the closed-loop units. The power supply cooling checks cover the 24 V side, and the sealed-enclosure layout article shows where to hang the drive so the air inside actually moves.
Mounting, glands and getting in safely
Hang the box so the highest breaker handle sits no more than 2.0 m [6 ft 7 in] above the floor, the limit NEC 240.24(A) sets. In front of it, NEC 110.26(A) wants at least 3 ft [900 mm] of clear depth at 0-150 V to ground, 30 in of width or the equipment width, and room for a 90-degree door swing. Land the cables through IP66 cord grips in the bottom wall, one cable per gland, and order the holes with the box: factory cutouts keep the rating, and the cutouts and glands guide lists the fitting sizes. One habit worth your fingers: kill and lock the feeder before you open the door, and give the drive's DC bus the discharge time its manual states, because it holds charge for minutes after power-off.
What to put on the order
| Line on the order | What to write for a machining cell |
|---|---|
| Rating | NEMA 4X / IP66, manufacturer-rated, not UL listed |
| Material | 304 stainless, #4 brushed; 316L for salt, brine, pharma |
| Size | The one that cleared the heat check: 48 x 30 x 12 in [1220 x 762 x 305 mm] in the example |
| Cutouts | Gland holes by cable OD on the bottom wall; window if the operator needs one |
| Inside | Removable mounting panel, about a quarter of it left free for the next drive |
| Delivery | 10 business days from your order, or from your approval of the drawing for a custom size |
Every stainless box from 6 x 4 x 4 in to 60 x 36 x 16 in is in the stainless size finder. Run your room, kit list and heat sum through the enclosure selector when you want a shortlist, or send the drawing to custom enclosures and have the exact size, grade and cutout pattern built from one piece.
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 | 304 stainless | 20 x 16 x 8 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 |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can a drive live in a repurposed PC or rack-mount case?
Only in a dry, clean room and only as a bench solution: those cases carry no enclosure type, and their vent slots pass coolant mist and chips straight to the boards. The heat math still applies: 100 W inside a case the size of a 20 x 16 x 8 in enclosure lifts the air about 35 C. Near any machine coolant, order a sealed NEMA 4X / IP66 stainless box instead.
How many watts does a VFD add to the enclosure heat load?
Plan on 2-4 % of rated output at full load: a 5 hp (3.7 kW) drive dissipates 75-150 W, or 111 W at the 3 % midpoint. The drive's datasheet prints the exact loss figure, and that number wins once you have it. Add the supply's loss, about 13 W for a 120 W unit at 90 % efficiency, plus 5-15 W of relays, coils and terminals in a small panel.
Does a fan and filter kit keep the NEMA 4X rating?
The cabinet drops to the fan-filter's rating the day you cut the hole, and most washable filter sets sit around IP54 as their makers mark them. That is fine in a dry Type 12 room. To keep 4X near coolant, cool with a closed-loop air-to-air heat exchanger or an enclosure air conditioner; both move heat with the door seal intact.
304 or 316L stainless for the drive box?
Order 304 for indoor machining cells, food and beverage washdown and most outdoor walls; order 316L where salt air, brine or chloride-bearing cleaners reach the box, and for pharma suites. Chlorides pit 304 even at room temperature under a deposit, and about 60 C is the stress-corrosion threshold for both grades, so hot plus salty means 316L plus a cooler.
What size enclosure for one 5 hp drive, its supply and relays?
At a 25 C room you need about 2.4 m² [3,740 in²] of wall for the 134 W total, which a 48 x 30 x 12 in box delivers with a 37 C interior. In a 35 C room the same load wants 7.2 m², past even a 60 x 36 x 16 in box, so size the wall only in cool rooms and fit closed-loop cooling in hot ones.
