Short answer: for a 5 hp [4 kW] motor, order a 12 x 10 x 6 in [305 x 255 x 150 mm] stainless box, manufacturer-rated NEMA 4X-type / IP66, and put the pushbuttons on the door as IP66 operators. The starter — motor-protection circuit breaker, 9 A contactor, one auxiliary block and a control terminal strip — takes about 175 mm [6.9 in] of DIN rail and sheds about 10 W, which this box holds to an 8 C rise at 40 C ambient. The compact enclosures sold to fit a single protective device take the breaker and its side auxiliaries only, so once a contactor is on your parts list you size the enclosure around the whole assembly. Here is that sizing, with the arithmetic.
What goes on the rail
Start from the motor. A 5 hp three-phase motor draws 7.6 A full load at 460 V, or 15.2 A at 230 V. Set the breaker dial to 7.6 A; its magnetic band, about 13 x that setting on most motor-protection breakers, rides through inrush. A 9 A AC-3 contactor (5.5 kW at 400 V) carries the motor with headroom, and 14 AWG copper conductors sized at 125% of full load — 7.6 x 1.25 = 9.5 A against 20 A capacity — close the circuit. Now count rail:
| Part | Rail width |
|---|---|
| Motor-protection circuit breaker, 16 A frame, dial set to 7.6 A | 45 mm [1.8 in] |
| Contactor, 9 A AC-3 | 45 mm [1.8 in] |
| Two-contact auxiliary block, side-mounted on the contactor | 25 mm [1.0 in] |
| Control terminal strip, 12 two-level positions | 60 mm [2.4 in] |
| Total for a 5 hp starter | 175 mm [6.9 in] |
A four-contact side block instead of two contacts adds about 45 mm [1.8 in], not 25 mm, so add 20 mm to the total if you wire more signalling. Hold that 175 mm figure; the sizing below turns it into a box.
Why the one-device compact box stops there
The small enclosures engineered around one protective breaker give you about 70 mm [2.8 in] of rail: the breaker body plus the auxiliary blocks that clip beside it. Their instructions show exactly that arrangement and nothing more. The contactor is a second 45 mm body with its own lug clearances, and in those boxes it has nowhere to land.
So build the assembly yourself in a general-purpose enclosure. You choose the rating, the grade and the door cutouts, and the box arrives cut to your drawing. Treat the one-device box as what it is — a breaker housing, not a starter housing.
What IP65 covers at the machine
IP65 is two tests under IEC 60529. The first digit 6 is dust-tight: no dust enters. The second digit 5 is jets: a 6.3 mm [0.25 in] nozzle delivering 12.5 L/min [3.3 gal/min] from 2.5 to 3 m [8 to 10 ft], for at least 3 min, from any direction, with no harmful effect. That covers splash, wipe-down and a low-pressure rinse — a pump pit's spray, a food line's gentle rinse. A washdown hose is the IPX6 test, a 12.5 mm [0.5 in] nozzle at 100 L/min [26 gal/min], so in washdown areas order more than IP65.
Our wall-mount boxes carry a manufacturer rating of NEMA 4X-type / IP66, which covers both jet tests with margin; they are not UL listed, and NEMA itself does not test or certify enclosures. In US installations, NEC 110.28 treats an IP code as no replacement for an enclosure type rating, so a spec written as NEMA 4X needs the type — a dual-marked box satisfies both worlds. The IP rating chart and the NEMA 4X vs IP66 comparison carry the full digit tables.
Sizing the box: rail, gutters, depth
Take the 12 x 10 x 6 in 304 stainless box. Its mounting panel gives you about 230 mm [9.1 in] of usable rail after the panel edges. Your 175 mm of devices leaves 55 mm — 32% spare, just past the 30% you want for a second auxiliary block or a few more terminals later. Stack it top to bottom: 2 in [50 mm] of clear gutter above the rail for the incoming lugs, the rail with its devices, 2 in below for the outgoing motor cable, and the control terminals near the bottom. Inside height is 11.91 in [302 mm], so the stack fits with room for a second rail.
Wiring duct changes the arithmetic. One 1 in [25 mm] duct down each side takes 50 mm off the rail, and at 50% wire fill — the NFPA 79 duct-fill figure our backplate and DIN rail layout guide uses — a 25 x 60 mm duct holds about 750 mm² [1.2 in²] of copper, plenty here. But your spare rail is gone, so step to the 12 x 12 x 6 in 316L box: about 280 mm [11 in] of usable rail, 60% spare bare or 30% with both ducts fitted.
Depth is the quiet constraint. A 45 mm-frame breaker with lug tops out near 90 mm [3.5 in] from the panel; the box's 5.91 in [150 mm] inside depth leaves about 60 mm [2.4 in] to the closed door. That clears a contactor with ring lugs and front-mounted auxiliaries. The enclosure sizing guide covers the panel-clearance rules behind these gaps.
The heat check on a sealed box
Where does 10 W come from? A 9 A contactor running 7.6 A loses about 1 W per pole, or 3 W; its AC coil holds 2-4 W; the breaker adds under 1 W; lugs and wiring about 1 W. Call it 10 W and design to that number.
A sealed stainless box sheds heat through its walls, and surface does the work. The 12 x 10 x 6 in box has 0.325 m² [3.5 ft²] of surface, and stainless transfers about 3.7 W per m² per C, so the box sheds 3.7 x 0.325 = 1.2 W for every degree of rise. At 10 W: 10 ÷ 1.2 = an 8 C rise. In a 40 C [104 F] plant the air inside sits near 48 C, which switchgear built to IEC 60947 — rated at 40 C ambient — carries without complaint. The enclosure thermal resistance method generalizes this to any box and load.
Two things push the number up. A 24 V control supply or a small PLC rides along at 5-10 W, and 15 W in this box means a 12 C rise. Full midday sun adds about 200 W per m² of sunlit face to a light stainless door — roughly 15 W on this box's 0.08 m² [0.8 ft²] door, as much as the starter itself. Either way you want surface: the 16 x 14 x 6 in box has 0.52 m² [5.6 ft²], sheds 1.9 W per degree, and holds a 20 W load to about a 10 C rise.
Keep the box sealed. A vent, drain or fan-filter carries its own rating, and the weakest part sets the assembly's rating — an IP54 filter on this door makes it an IP54 box. Your starter needs no airflow; the vent or sealed-box decision matters when the load is ten times this one.
Buttons and the breaker on the door
You want to run the motor without opening the door, so put the controls through it. Ø22 mm [0.87 in] pushbuttons and selector switches carry their own front rating — IP66 or better on most industrial operators — seal into a punched hole with a collar gasket, and take a snap-on contact block on the inside. Start, stop, hand-off-auto and a feedback lamp fit comfortably on a 10 in [255 mm] wide door with spacing your gloves will thank you for.
Have the holes cut when the box is built. Sealing an IP65 instrument cutout is what keeps each hole at the box's rating, and the cutouts, glands and windows guide lists what to send with the drawing. Spare holes get rated blank covers; DIN panel cutout fillers for NEMA-rated doors explains the options, and a snap-in plastic plug is not one of them. For the breaker itself, a door-interlocked rotary handle for the breaker gives you on-off at the door with the rating intact. Lock out the feeder and prove it dead before you work inside.
Cable entries, gasket and ground
Cables enter through the bottom wall only, in glands sized to the cable's outside diameter — an M25 [1 in] gland for a 12 mm OD motor cable, M20 for control — and the top wall stays blank so nothing drips into a hole. A gland clamped on an undersized cable leaks at the seal; sealing a gland around a smaller cable shows the fix. Conduit runs use threaded hubs with sealing rings.
At commissioning, run a finger around the door gasket path and clear anything you find. One wire strand or paint chip under a door gasket is a leak you will meet at the first wash. Bond the door and the mounting panel to the box with a bonding strap, and land the equipment grounding conductor on the same stud — the grounding and bonding guide has the sizing table.
Material and mounting height
Grade comes from the environment. 304 stainless carries most indoor and general outdoor duty. Move to 316L when chlorides reach the box: salt air near the coast, brine, food plants running hypochlorite sanitizers, pharma clean-down. Both grades come as the same wall-mount enclosure with hinged gasketed door, mounting panel and wall-mount feet.
Height: NEC 110.26(A) sets clear working space in front of equipment serviced energized — 3 ft [900 mm] of depth at the lowest voltage band and room for the door to open 90 degrees, with a 480 V system a band up at 3.5 ft [1.1 m]. NEC 240.24(A) keeps the highest operating handle at or below 6 ft 7 in [2.0 m]. Set the top edge of a 12 in [305 mm] tall box at 60 in [1.52 m] and both numbers clear with margin.
What to put on the order
| Line | What to write | 5 hp example |
|---|---|---|
| Enclosure | Stainless wall-mount, hinged door, mounting panel | 12 x 10 x 6 in [305 x 255 x 150 mm] |
| Rating | Manufacturer rating | NEMA 4X-type / IP66, not UL listed |
| Grade | 304 general duty; 316L for salt or chlorides | 316L on a food line |
| Rail load | Devices plus 30% spare | 175 mm on about 230 mm of rail |
| Door cutouts | Ø22 mm operator holes with rated covers | 3 buttons, 1 selector |
| Bottom cutouts | Gland holes to cable OD | 1 x M25, 2 x M20 |
| Option | Rotary handle for the breaker | door-interlocked |
| Delivery | 10 business days | from order; custom from drawing approval |
Decision by case: a 5 hp starter indoors takes the 12 x 10 x 6 in 304 box. The same starter with side duct and a control supply takes the 12 x 12 x 6 in box. Hose washdown or a coastal outdoor wall takes the 316L version, and in sun one size up for the solar load or a shaded wall. Above 10 hp, run the same three numbers — rail, depth, watts per degree — and the box picks itself. The enclosure selector walks those inputs, and custom enclosures take any cutout drawing you draw.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 316L stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 12 × 6 in | 316L stainless | 12 x 12 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 6 in | 304 stainless | 16 x 14 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
What size enclosure does a 10 hp motor starter need?
A 10 hp 460 V motor draws about 14 A, so the contactor moves to a 25 A AC-3 frame (still a 45 mm [1.8 in] body) and the protection breaker steps up one frame to about 55 mm [2.2 in]. With auxiliaries and terminals you are near 185-200 mm [7.3-7.9 in] of rail, which a 14 x 12 x 6 in [355 x 305 x 150 mm] box carries with 30% spare. Its 0.42 m² surface keeps a 12 W load at about 8 C rise.
Can the contactor go in a compact breaker enclosure?
No. Those boxes are laid out for the protective device and the auxiliary blocks that clip beside it — roughly 70 mm [2.8 in] of rail — and the instructions show nothing else. The contactor is a second 45 mm [1.8 in] body with its own lug clearances and no place to land. Build the assembly in a box sized around the whole parts list; you also gain the door area for the buttons you want.
Is IP65 enough for hose-down cleaning?
No. The IPX5 test is a 6.3 mm [0.25 in] nozzle at 12.5 L/min [3.3 gal/min] — splash, wipe-down and rinse territory. A washdown hose runs closer to the IPX6 test: a 12.5 mm [0.5 in] nozzle at 100 L/min [26 gal/min]. Order a box rated NEMA 4X-type / IP66 and both jet tests are covered with margin.
What happens to the starter box at 50 C ambient?
Add your rise to it: 50 C plus 8 C puts the inside near 58 C. Switchgear built to IEC 60947 is rated at 40 C ambient, and datasheets commonly publish a derating factor around 0.8-0.9 x rated current at 60 C surroundings. Take the derate, or fit the 16 x 14 x 6 in box, whose 0.52 m² surface drops the rise from 8 C to about 5 C.
How fast can a box with custom door cutouts arrive?
Delivered in 10 business days anywhere in the world — counted from your order for a catalog box, and from your approval of the drawing for custom cutouts. Send the cutout drawing with hole sizes and positions when you request the quote, so the clock starts at approval rather than at a round of questions.
