Sealed enclosure for six AC servo drives: sizing the heat load

Short answer: budget 2-3% of each AC servo drive's continuous rating as heat, add the 24 V DC supply and the panel PC, and size a closed-loop cooler on the total. Six axes totalling 7.1 kW put about 270 W into a sealed 24 x 36 x 8 in [610 x 915 x 200 mm] stainless cabinet, and the walls of that box shed only about 6.4 W per kelvin. The inside therefore settles 42 K above the shop, near 67 °C in a typical shop, some 27 K past the 40 °C ambient most drives carry. The fix is a manufacturer-rated NEMA 4X / IP66 air-to-air heat exchanger, or a small enclosure air conditioner. Sealed stays the right call around coolant mist and metal dust; it just has to be sealed with a real cooler instead of vents.

How much heat do six servo drives put into a cabinet?

Budget 20-30 W of heat for every kilowatt of continuous servo drive rating, the band manufacturer watt-loss tables print for AC servo drives near rated load: six axes totalling 7.1 kW therefore add 142-213 W before you count the supply or the PC.

Work the list axis by axis: two 0.75 kW axes, two 1.8 kW axes and two 1.0 kW axes come to 7.1 kW, and 7.1 kW x 3% = 213 W at the hot end, 142 W at 2%. Add the rest of the panel: a 24 V DC supply delivering 82 W loses about 15 W at an assumed 85% efficiency, and assume a small industrial PC adds 40 W until you swap in its real rating. The estimate lands at 268 W, so 300 W is the design number for the cooler.

Duty moves the drive figure by about 1% of rating either way. An axis that creeps between light cuts sits near the 2% end; hard stops that push regenerative energy back through the brake resistor run toward 3% and a little past. The same watts-in budget sizes any sealed box: sizing a sealed enclosure for a PoE switch heat load runs it for network gear.

What does a sealed 24 x 36 x 8 in box do with 270 W inside?

A sealed stainless box of that size transfers about 6.4 W per kelvin through its walls, so 270 W lifts the inside air 42 K above shop ambient, well past the 40 °C ambient most drives carry.

The arithmetic sits in three lines:

• Wall area: 2 x (0.61 x 0.91 m) + 2 x (0.61 x 0.20 m) + 2 x (0.91 x 0.20 m) = 1.72 m² of stainless surface.
• Wall conductance: 3.7 W/m²K x 1.72 m² = 6.4 W/K, the still-air value for a stainless wall that the sizing guides here use.
• Rise: 270 W / 6.4 W/K = 42 K, so the cabinet rides 42 K over the shop.

Every 10 W removed buys back about 1.6 K. Conduction alone holds this cabinet inside limits only up to 96 W for a 15 K margin (6.4 W/K x 15 K), about a third of the load. The stepper-drive heat check runs the same wall-loss sum for smaller cabinets and meets the same wall a few hundred watts up.

Which rating and material does a machine-shop cabinet need?

Specify a manufacturer-rated NEMA 4X / IP66 cabinet in 304 stainless for a coolant-mist shop, stepping up to 316L where washdown uses chloride cleaners or the air is salty; both grades enter the chloride stress-corrosion band above about 60 °C [140 °F].

NEMA 250 defines Type 4X as a corrosion-resistant enclosure that stays watertight under hose-down, with a 200-hour salt-spray test stacked on the Type 4 sequence. IEC 60529 defines IP66 as dust-tight (first digit 6) and sealed against powerful jets from a 12.5 mm nozzle at 100 L/min (second digit 6). Our wall-mount cabinets carry both marks, rated NEMA 4X / IP66 by the manufacturer; they are not UL listed. In US installations NEC 110.28 treats IP codes and enclosure type ratings as separate marks, so a drawing that calls out Type 4X carries the NEMA type too. The NEMA 4X vs IP66 rating guide lays out the test differences, and drive enclosure choice: rating, size and cooling makes the same call for a single drive.

On the metal: 304 holds in most machine shops, while chloride deposits that dry onto it can pit the surface even at room temperature, so rinse the cabinet or step to 316L, whose molybdenum lifts pitting and crevice resistance. The 60 °C [140 °F] stress-corrosion threshold sits at the same place for both grades; only the pitting margin differs.

Why seal the cabinet instead of fitting a fan-filter?

Seal it: a fan-filter trades 270 W of heat for a steady intake of coolant mist and conductive metal dust, and any breather, drain or filter that is not itself rated Type 4X / IP66 pulls the whole cabinet down to that part's rating.

A sealed box keeps the shop outside; the only paths left are the walls and the exchanger's closed loop. The catch is the seams. A stainless cabinet with an unrated plastic vent is a vent with a stainless border, because the assembly rating drops to the lowest-rated part. Whether a breather vent keeps a NEMA 4X rating walks that check vent by vent, and the door gasket earns the same glance after every washdown.

How do you size the heat exchanger or air conditioner?

Size a closed-loop air-to-air heat exchanger as load divided by the temperature difference you can afford: holding 40 °C inside against a 25 °C shop gives 300 W across 15 K, so a unit rated at least 20 W per K keeps the drives inside their limit.

Manufacturers quote exchanger capacity at a stated temperature difference, so convert before comparing: at that rating the 268 W load rides about 13 K above the shop, near 38 °C inside, under the 40 °C line with margin. Shop temperature is the swing factor. At 35 °C the affordable difference collapses to 5 K, and the 300 W design load then needs 60 W/K, which is where the air conditioner takes over: pick an enclosure AC with published cooling capacity above 300 W, and a 500 W class unit leaves margin for a fouled condenser. Either way the cooler itself must carry the Type 4X / IP66 rating, or the cabinet drops to whatever the cooler holds.

The fan vs air conditioner vs heat exchanger comparison sorts the three by dust load, and the heat pipe air-to-air heat exchanger design calculations page works this W/K arithmetic in more detail.

How do you lay out the cabinet so the cooling still works?

Mount the drives with their heatsinks flat on the backplate, leave 2 in [50 mm] of clearance above each one, and keep 20-25% of the mounting panel spare so a seventh axis or a larger PC still has somewhere to go.

Heat stratifies in a sealed box, so put the 24 V supply low, the drives mid-panel, and the PC clear of the exchanger's return air. A small EC circulation fan evens the gradient so the walls and exchanger see average air; mixing moves no heat out by itself. Cut the cable entries on the drawing, sized for the glands you will fit, and latch the door evenly so the gasket seals all round. One safety line: lock out and verify absence of voltage before the first terminal.

For service with the panel energized, NEC 110.26(A) asks for clear working space in front, at least 3 ft [900 mm] deep for 0-150 V to ground in Condition 1, with room for the door to open 90°, and NEC 240.24(A) holds the highest breaker handle at or below 2.0 m [6 ft 7 in].

What do you put on the order?

Order a 36 x 24 x 8 in [915 x 610 x 200 mm] 304 stainless wall-mount cabinet with hinged gasketed door, removable mounting panel, and cutouts drawn for the glands and the heat exchanger, delivered in 10 business days from your approval of the drawing.

Two numbers carry the most weight on the quote request: the 300 W design heat load and the 15 K difference it assumes against shop ambient.

The enclosure selector turns environment, inside size and cooler type into a shortlist, and the stainless size finder filters 304 and 316L wall-mount boxes from 6 x 4 x 4 in up to 60 x 36 x 16 in [152 x 102 x 102 to 1,524 x 914 x 406 mm].

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.

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