A 10 hp three-phase fan runs from a 240 V single-phase supply, but the drive that bridges them needs help: single-phase input derates a VFD to roughly half its three-phase rating, so the order is a 20 hp class drive. Put that drive in a sealed 304 stainless wall-mount box and size the enclosure from the drive's heat, not the motor's horsepower: about 280 W inside at full speed. A sealed box sheds too little of that on its own walls, so add a 500 W class enclosure air conditioner, or cap the fan at 60% speed and let a 60 x 36 x 16 in box cool it passively. Feed it with 6 AWG copper on a 60 A two-pole breaker.
Which enclosure does a 10 hp fan on single-phase power need?
A sealed Type 4X 304 stainless wall-mount enclosure around a 20 hp class drive is the package: the drive derates to carry the 10 hp, and the sealed rating keeps rain out at the fan.
Single-phase input pushes the same power through a two-leg rectifier, so drive manuals derate the input to about 50-65% of the three-phase output rating. At the 65% end, a drive sold as 15 hp carries 9.75 hp continuously, just under the 10 hp, so the 20 hp class is the order. Keep the box sealed: rain and irrigation spray reach anything mounted at a fan, and any vent or fan-filter fitted to a Type 4X box pulls the whole assembly down to that part's rating.
Where should the drive sit: next to the motor or back at the panel?
Either spot works: the buried three-conductor run to the fan becomes the drive's output cable, so the only new circuit is the 240 V single-phase feeder at 6 AWG copper.
Choose by shade and access, not by electrical advantage. A drive at the panel shares working space you already have; a box at the fan shortens nothing, because the feeder follows the same trench. Stay inside the motor-cable length the drive manual lists before it demands an output reactor. Ohm out the windings before spending money: a healthy Class F 208-230/460 V motor usually runs fan duty without drama. Weigh both spots in the article on a VFD in the main control enclosure or a remote box.
What environment does the box face at an outdoor fan?
Rain, sun and irrigation splash set the floor at a sealed enclosure rated NEMA 4X / IP66 by the manufacturer; not UL listed, in 304 stainless for most fields and 316L near salt, brine or fertilizer drift.
Type 4 covers hose-directed water and 4X adds the corrosion grade; the same box exists in the salt-air grade as a 36 x 24 x 12 in 316L wall-mount enclosure. NEMA writes the type definitions but tests no boxes, and in US installations NEC 110.28 says an IP code does not replace the enclosure type rating. Carry both marks: NEMA 4X and IP66 together satisfy US and international sheets. The rating lives only on a sealed box; the fundamentals sit in the NEMA 4 vs 4X vs IP66 guide. Direct sun adds 10-20 C to a stainless wall, so pick a shaded wall or add that rise to the cooling budget.
How much heat does a single-phase-fed 10 hp drive add?
Size the enclosure from about 260 W of drive loss, not the motor's 10 hp: 7,460 W of output × a 3% loss × a 1.15 single-phase penalty, plus 20 W of control power, is a 280 W design load.
The motor sits outside the box, so its shaft power never loads the enclosure. The 3% figure is the usual selection-calculator fallback for a modern drive near full load. The loss in watts printed on the drive datasheet beats it when it exists, and the 15% extra reflects the two-leg rectifier running hotter. Work the whole panel the same way with the guide to calculating enclosure heat load from component losses; the one-drive version of this sizing is in VFD enclosure rating, size and cooling for one drive.
Can a sealed box shed that heat on its own?
Not at full speed: even the largest wall-mount box here, 60 x 36 x 16 in with 3.0 m² of usable wall, sheds 111 W at a 10 K rise, so the full-speed load lands 25 K above ambient, near 55 C inside on a 30 C day.
The arithmetic for the 60 x 36 x 16 in 304 box, counting front, two sides and top: stainless conducts 3.7 W/m²K through the wall. Front 1.524 m × 0.914 m = 1.39 m²; two sides 2 × (1.524 m × 0.406 m) = 1.24 m²; top 0.914 m × 0.406 m = 0.37 m²; total 3.00 m². The shell moves 3.7 × 3.0 = 11.1 W per kelvin, and a 40 C ambient, the figure most drive datasheets set, allows a 10 K rise over a 30 C day: 111 W against the 280 W load. The gap needs cooling hardware that keeps the rating.
| How the fan runs | Heat inside the box | Cooling that keeps the rating |
|---|---|---|
| Continuous at full speed | 280 W | 500 W class enclosure air conditioner, or an air-to-air exchanger of 28 W/K or more |
| Continuous, speed capped at 60% | 75 W | Passive: the 60 x 36 x 16 in box, about a 7 K rise |
An air conditioner near 500 W [1,700 BTU/h] gives 1.8× margin and wins as ambient climbs: at 35 C the exchanger would need 280 ÷ 5 = 56 W/K, past the 15-50 W/K that exchanger datasheets typically list. The 60% cap works by the cube law: fan power falls to 0.6³ = 21.6% of 7,460 W, drive loss to about 56 W, and 20 W of control makes 75 W total, a 7 K rise and about 37 C inside, under the 40 C rating. Bigger loads and hotter sites are in outdoor drive enclosure cooling for high-power equipment; the exchanger side is in NEMA 4 heat exchanger requirements for drive enclosures.
What size enclosure fits a 20 hp class drive?
Start from the drive footprint, add the manual's heatsink clearance, typically 4 in [100 mm] above and below, then add terminal room and 25% spare width: a 36 x 24 x 12 in stainless wall-mount box is the usual landing.
The 36 x 24 x 12 in 304 box gives you room for the drive, its input terminals and the cooling-unit cutout in the wall; the inside dimensions are on the product page. A smaller footprint trims to the 30 x 24 x 10 in box. Mount on wall feet, low enough that the breaker handle inside stays at or under 2.0 m [6 ft 7 in] above the floor under NEC 240.24(A). Keep 3 ft [900 mm] clear in front under NEC 110.26(A), the working-space figure for a 120 V-to-ground supply. Stock sizes live in 304 and 316L wall-mount enclosures; any other dimension comes from custom enclosures, and the enclosure selector narrows by environment and inside size.
What goes through the wall and onto the order?
Feed it with 6 AWG copper on a 60 A two-pole breaker, land the output on the buried conductors at 8 AWG copper or larger, and bring a 10 AWG equipment grounding conductor into a bonded gland plate.
The input draws about 48 A at 240 V: the same power through two legs instead of three lifts current 1.73× over the 28 A three-phase figure. The 125% sizing on the drive's rated input current under NEC Article 430 lands on that breaker with 6 AWG copper, whose 75 C column ampacity of 65 A covers it. The output carries 28.5 A of motor full-load current; at 125% that is 35.6 A, so 8 AWG copper (50 A) covers new conductors or the buried ones.
Bond the enclosure and the motor frame to the same 10 AWG copper EGC, sized from the breaker under NEC Table 250.122. The earth is not an effective fault-current path under NEC 250.4(A)(5), and bare stainless needs no coating scraped at the stud, as the grounding and bonding guide details. Cut two bottom glands to the cord or conduit OD, per the cutouts and glands guide. At the full-speed heat load the running box stays above the night dew point, so it needs no anti-condensation heater.
| Order line | What to specify |
|---|---|
| Enclosure | 36 x 24 x 12 in 304 stainless wall-mount, manufacturer-rated NEMA 4X / IP66 (316L at salt, brine or fertilizer sites) |
| Cooling | Side cutout for a 500 W class enclosure air conditioner, or an air-to-air exchanger of 28 W/K or more |
| Cutouts | Two bottom glands: 6 AWG feeder in, motor output out, plus a bonded EGC stud |
| Mounting | Wall feet, shaded wall, breaker handle at or under 2.0 m [6 ft 7 in], 3 ft [900 mm] clear in front |
| Drive and feeder | 20 hp class, 240 V single-phase input / 230 V three-phase output, 60 A two-pole breaker, 6 AWG Cu feeder, 10 AWG Cu EGC |
Everything above is built to order and delivered in 10 business days, counted from your approval of the drawing.
Enclosures in this article
| 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 |
| 36 × 24 × 12 in | 304 stainless | 36 x 24 x 12 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 |
| 36 × 24 × 12 in | 316L stainless | 36 x 24 x 12 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can a single-phase VFD run a 10 hp three-phase motor?
Yes. Manuals derate single-phase input to about 50-65% of the three-phase rating, so a 20 hp class drive carries 10 hp continuously and draws about 48 A at 240 V. Mind the service too: the two-pole branch takes over half of a 100 A panel, so add the existing loads before you commit the feeder.
Does the fan motor need inverter-duty insulation?
Look at the nameplate before ordering: a Class F, 208-230/460 V motor on fan duty is the common case and runs on a drive set to its manual. Inverter-duty insulation matters most on long motor cables and high carrier frequencies; stay inside the manual's cable length or fit the filter it names.
How hot can the ambient get before the passive box fails?
About 33 C ambient for the passive path: the 60 x 36 x 16 in box settles near 37 C inside on a 30 C day, about 3 K under the 40 C drive rating. Above that, the 500 W class air conditioner holds the full-speed load.
What breaker protects a drive on single-phase input?
Fit an HACR-rated breaker or a time-delay Class J fuse pair ahead of the drive. A Class J fuse carries five times its rating for at least 10 s (UL 248-8), which rides through the DC bus charge inrush; a standard fast magnetic breaker nuisance-trips on that same inrush even when sized at 125% of input current. Check the drive manual's protective-device wording before you order.
Will 304 stainless hold up at an irrigation fan?
For most fields, yes, in the brushed #4 finish. Order 316L within salt air of a coast, brine or fertilizer drift. Both grades share the same 60 C [140 F] chloride stress limit, and this box stays under it inside while running.
