Short answer: move a servo drive out of the cabinet for cooler machine air, a shorter motor cable, or a clean boundary between your cabinet crew and a contractor's drive crew. Everything else travels with it: the drive's heat, its enclosure rating and its spares strategy. Heat is the part engineers underestimate. In the worked example below, a 90 W servo drive needs about 2.4 m² [26 ft²] of stainless surface to hold 40 °C (104 °F) on a 30 °C (86 °F) day. That surface follows the drive wherever it sits. Keep the drive in the cabinet when the machine spot runs hotter than the panel room; move it out when it does not.
The two architectures, side by side
You land power, network and feedback on the drive either way, so wiring is not the difference. The difference is where the drive's heat goes, which box protects it, and whose hands touch it at 2 a.m.
| Point to decide | Drive in the cabinet | Drive at the machine |
|---|---|---|
| Air at the drive | Panel-room air plus the cabinet's internal rise: 43.5 °C in the example | Machine air at the mounting spot, plus motor heat and, outdoors, sun |
| Enclosure protecting it | The main cabinet, one rating for everything inside | A second box you buy, mount and seal, or the drive maker's own housing |
| Motor cable | 25 m (82 ft) routed in the example, past a 20 m (66 ft) example manual limit | 2 m (6.6 ft), the shortest practical path |
| Heat path | Cabinet walls, or a closed-loop panel cooler | The machine-side box's own walls |
| Spares | Any drive of the right rating pairs with the motor | Often a fixed motor-and-drive set |
| Service boundary | Cabinet and drive share one room and one crew | Drive replacement at the machine can go to a contractor |
| New failure points | A panel cooler failure heats a sealed cabinet fast | Exposed glands, connectors and mounts in the washdown zone |
The example behind these numbers is one 3 kW axis with a drive that loses 90 W and 60 W of controls. Replace every input with your own manual values before you order anything.
Where the cabinet drive wins
Hot spots are the strongest case for keeping the drive inside. Suppose the mounting spot reads 35 °C (95 °F) while the panel room sits at 30 °C. The machine-side box then loses half its headroom: the allowed rise falls from 10 K to 5 K. The surface it needs doubles, from about 2.4 m² [26 ft²] to 4.9 m² [53 ft²]. Measure the spot with a thermometer during a hot production run, not on a cold morning in a shut-down hall.
The cabinet also keeps one rating to maintain. Everything inside shares the cabinet's Type rating; at the machine, every gland, connector and foot has to earn its own. Multi-axis machines add a second argument: several drives share one layout, one spares shelf and one cooling budget. The layout work is in multi servo drive enclosure layout and sizing, and the per-drive sequence of rating, size and cooling is in VFD enclosure size and cooling — the same method covers a servo axis.
Spares stay flexible in the cabinet. A cabinet drive pairs with any motor of the right feedback family. Many machine-mounted drives are sold as a motor-and-drive set, so the next replacement locks you into the same pairing. If the axis crosses a slip ring, a motor-mounted drive adds power and feedback crossings for the ring to carry. Keep the drive off the joint unless the ring was sized for them.
A closed-loop panel cooler is the third way to hold a hot cabinet. Size it for the whole internal load at the site's peak: 150 W in the example, which a 500 W-class unit carries with margin. Mount it where condensate drains and the service side stays reachable; side vs roof mounting covers the placement call. Its failure mode is real: a sealed cabinet climbs fast when the cooler dies, so alarm the unit and treat the alarm as a machine stop. Where the choice is between cooler types, thermoelectric vs air conditioner sorts small loads from large ones.
Where the drive at the machine wins
Cooler air is the win that pays. A frame in a cooled hall, away from the gearbox and out of the sun, is the spot that works. The drive leaves the hottest box in the plant, and the cabinet's load falls with it. Hold the spot to the same ambient ceiling you would apply to distributed I/O in a hot cell; decentralized I/O in high ambient temperature applications walks that derating logic for 40-50 °C sites.
The motor cable is the second win. The example route ran 25 m (82 ft) from cabinet to motor, past the 20 m (66 ft) example manual limit; at the machine it falls to 2 m (6.6 ft). Shorter runs cut copper losses and put less switching edge into the motor winding. Read the manual's cable limit, use shielded cable, and count both the power and feedback cables as routed lengths, not straight-line distances.
The service boundary is the third win, and it is organizational rather than electrical. Drive replacements go to the contractor's crew; cabinet work stays with your electricians. A box at the machine draws that line physically. You also stop reserving dead cabinet space for a next-generation drive of unknown dimensions, because the machine pad takes whatever comes next.
The cabinet shrinks too. With the drive gone, its load falls from 150 W to 60 W, and the wall area the cabinet needs falls from 4.05 m² [44 ft²] to 1.62 m² [17 ft²]. That is the difference between a floor-standing cabinet and a wall-mount box of about 32 × 24 × 10 in [800 × 600 × 250 mm].
The heat math that decides it
A sealed stainless box in still air sheds heat through its walls at this site's reference rate, k = 3.7 W/m²·K. The rise over ambient is ΔT = P / (k × A), with P the watts inside and A the exposed wall area. The example inputs, all replaceable with your own:
- Drive: 3 kW servo axis, declared loss 90 W — a worked-example figure near 3% of rating; your manual's loss table wins.
- Controls: 60 W of power supply, controller and I/O.
- Air: 30 °C (86 °F) panel room; machine spot at 30 °C in the good case and 35 °C (95 °F) in the hot case.
- Target: 40 °C (104 °F) at the drive, the default design ambient for drives and most electronics. Many servo manuals list 0-50 °C with a derating curve at the top of the range; many industrial drive datasheets give 0-40 °C at under 90% relative humidity, non-condensing. Design to 40 °C unless your datasheet's curve allows more.
Five calculations settle the argument:
- Everything in the cabinet. P = 150 W. A floor-standing shell with 3.0 m² of exposed wall gives ΔT = 150 / (3.7 × 3.0) = 13.5 K, so the drive sits at 43.5 °C — 3.5 K over target.
- Passive area the cabinet would need. A = 150 / (3.7 × 10) = 4.05 m², still air assumed. The full cabinet-sizing method, wire space included, is the enclosure sizing guide.
- Drive moved out. The cabinet carries 60 W and needs A = 60 / (3.7 × 10) = 1.62 m². A shell of about 32 × 24 × 10 in presents 1.66 m², so ΔT = 60 / (3.7 × 1.66) = 9.8 K and the controls land at 39.8 °C. The smaller cabinet works.
- The drive's own box at a 30 °C spot. A = 90 / (3.7 × 10) = 2.43 m². A box of about 40 × 32 × 10 in [1000 × 800 × 250 mm] presents 2.5 m², so ΔT = 90 / (3.7 × 2.5) = 9.7 K and the inside lands at 39.7 °C. It fits — and the drive's box is nearly as big as the cabinet you just shrank.
- The same box at a 35 °C spot. The allowed rise is 5 K, so A = 90 / (3.7 × 5) = 4.9 m² — bigger than the cabinet you escaped. That is the whole trade in one line.
The area scales with the watts: a 200 W drive at the same 30 °C spot needs about 5.4 m² [58 ft²]. Sun and warm neighbours eat the margin, because noon sun delivers roughly 1 kW/m² to a face pointed at it and a box bolted to a warm frame starts above air temperature. The outdoor correction is the method in an enclosure hotter than ambient.
Sizing the machine-side box
The box the drive moves into takes over the cabinet's old job. Order it with the same arithmetic:
- Surface first. Choose width, height and depth to give the area from the formula — about 2.43 m² [26 ft²] for the example drive at a 30 °C spot, which a 1000 × 800 × 250 mm [40 × 32 × 10 in] geometry provides with a small margin. Because the box is built to your dimensions, order the surface the heat needs and put the cutouts around it.
- Material. 304 stainless covers indoor washdown and most outdoor sites; 316L is the pick for salt air, brine, chlorides and chemical or pharma areas. Beside hot equipment, keep one figure in mind: chloride stress-corrosion cracking starts near 60 °C (140 °F) in both grades, so leave clearance between the box skin and a hot motor or steam line.
- Rating. For hose-directed water, order Type 4X. Our stainless boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed. The difference between the Type numbers, the extra salt-spray hours and the IP pairing is in NEMA 4 vs 4X vs IP66.
- Glands and cutouts. Every gland and blanking plug carries its own rating, and the weakest one sets the box's. The cutout and gland practice that keeps the number is in the cutouts, glands and windows guide.
- Mounting. Bolt through sealed feet or a sealed back plate so the fixings do not cost the rating; mounting a weatherproof box shows the details that survive a hose.
- The drive's own housing. A decentralized drive sealed IP65 (dust-tight, protected against jets) or IP67 (dust-tight, 1 m immersion for 30 min) by its maker carries an IEC mark. When a US specification calls for an enclosure Type number, the drive goes inside a box that has one. NEC 110.28 treats IP codes and enclosure Type ratings as separate systems in US installations.
The decision by environment
| Conditions at the machine spot | Decision |
|---|---|
| 30 °C (86 °F) or cooler, clean indoor machine | Move the drive out; order about 2.4 m² [26 ft²] of box surface, Type 4X if it gets hosed |
| 35 °C (95 °F) or hotter — beside the motor, in sun, near an oven | Keep the drive in the cabinet and cool the cabinet instead |
| Washdown or food plant | Move only into a 316L Type 4X box with matched glands and the 60 °C (140 °F) skin-clearance check |
| Outdoors, unshaded | Keep it in the cabinet, or shade and upsize the box before you trust the 2.4 m² |
| Dry, dusty cell | Either, with both boxes sealed; the dust practice is in a cabinet in a dusty machining cell |
| Axis crosses a slip ring | Keep the drive in the cabinet unless the ring carries the extra crossings |
A small cabinet near the motor, the middle path, passes or fails by the same two checks as a true decentralized drive: air at the spot, surface on the box.
What to specify
- A decision per axis, from the table above. Note the spot temperature you measured and the manual's motor-cable limit next to it.
- The machine-side box, when the drive moves: 304 or 316L stainless; dimensions chosen for the surface the heat needs, about 1000 × 800 × 250 mm [40 × 32 × 10 in] for the example drive at a 30 °C spot; Type 4X for washdown with matched glands; a gland plate low on the box where the conduits arrive.
- The cabinet, for the drives that stay: either the shrunken size from the arithmetic or the original shell with a closed-loop cooler, alarmed.
- The order itself. The machine-side box goes to the custom enclosure builder with your cutouts marked on the drawing; it is delivered in 10 business days, counted from your approval of the drawing. If the architecture call is still open, the enclosure selector narrows the choice by environment, listing and usable size first.
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
Does moving a servo drive out of the cabinet cut the heat load?
It moves the heat, it does not delete it. In the worked example the drive's 90 W leaves the cabinet and the cabinet load drops from 150 W to 60 W, but the drive then needs about 2.4 m² [26 ft²] of stainless surface at the machine to hold 40 °C (104 °F) on a 30 °C (86 °F) day. The architecture wins only where the machine spot stays cooler than the panel room.
How long can the servo motor cable be when the drive stays in the cabinet?
Use the limit printed in your drive manual; a representative figure for shielded cable is 20 m (66 ft), and the feedback cable usually sets a shorter one. The example route ran 25 m (82 ft), so the drive moved to the machine and the run fell to 2 m (6.6 ft). Treat 20 m as a worked-example figure and replace it with the manual's number.
What rating does the machine-side box need in a washdown plant?
Type 4X, for hose-directed water plus corrosion resistance; our boxes carry it as a manufacturer rating, not UL listed. Fit glands and plugs rated to the same level, because the weakest part sets the assembly. A drive housing marked IP65 or IP67 by its maker does not hand you a Type number for a US specification: NEC 110.28 treats the two rating systems as separate marks.
Is a small cabinet near the motor a good middle option?
Yes, when it passes the same two checks as a decentralized drive: air at the mounting spot and surface on the box. The example drive needs 2.4 m² of wall at a 30 °C (86 °F) spot; at 35 °C (95 °F) the need doubles to 4.9 m² [53 ft²], no smaller than the cabinet you were escaping. It also keeps the drive out of a fixed motor-and-drive pairing.
