Short answer: put the drive in the main enclosure when the box can give it 4 in [100 mm] of clear space top and bottom and dump its heat, and give it its own box when it cannot. For a 2 hp [1.5 kW] drive plus controls losing about 100 W, a sealed 12 x 12 x 6 in box runs 73 K above the room and cooks your drive. Keep that box for the motion controller and the 24 V supply, put the drive in a 20 x 16 x 8 box with a filtered fan, or bolt it beside the spindle in a cooled box of its own. Electrical noise is a wiring problem, not a placement problem, and the fixes are short.
Should the VFD go in the main control enclosure or its own box?
In the main box whenever the box has the drive's clearances and a way to dump its heat, and in its own box when the cabinet is tight, the drive is over about 5 hp [3.7 kW], or the environment forces sealed cooling.
Sharing one box saves a speed-reference cable between enclosures, one door gasket instead of two, and one place for you to troubleshoot. It costs space and heat: the drive's clearance zones and its 50-75 W land in the same volume as everything else. A separate box keeps the control enclosure small and cool, and it puts the drive near the motor for a short shielded cable run. The heat still has to leave that box, so you are trading one cooled enclosure for one sealed box plus one cooled box. For the layout side, read the CNC control enclosure sizing article; for the drive's own box, the VFD enclosure rating, size and cooling article.
How much clearance does a VFD need inside the enclosure?
Plan on 4 in [100 mm] of clear space above and below the drive and 2 in [50 mm] at the sides: those are the figures compact-drive installation manuals print, and bigger frames call for more.
The drive breathes through its fins, so the top and bottom zones matter most. A compact 2 hp frame stands about 8 in [200 mm] tall; with 4 in above and 4 in below, your drive alone claims 16 in [406 mm] of inside height. Add a frame width of about 5 in [125 mm] plus 2 in each side and it claims 9 in [230 mm] of width. Depth settles the box: a 2 hp frame runs about 6 in [150 mm] deep, and NEC 312.6 sets the wire bending space at terminals by conductor size, so the power conductors get their bending room behind the drive.
| Zone | Free space for a 2 hp frame |
|---|---|
| Above the drive | 4 in [100 mm] |
| Below the drive | 4 in [100 mm] |
| Each side | 2 in [50 mm] |
| Terminals | bending space per NEC 312.6, by wire size |
Keep ducts, the 24 V supply and the controller out of those zones; blocking the fins multiplies the temperature rise you compute below.
How much heat does a 2 hp VFD put into the panel?
Budget the full loss figure from the introduction: a 2 hp [1.5 kW] drive loses 3 to 5 % of its output at full load, call it 50 to 75 W, and the 24 V supply and controller add another 20 to 25 W.
Drive efficiency classes put compact VFDs at 95-97 %, which is where the 3-5 % comes from; your drive's datasheet prints the exact loss. Build the budget like this:
| Heat source | Basis | Loss |
|---|---|---|
| 2 hp [1.5 kW] drive at full load | 95-97 % efficient | 45-75 W |
| 24 V, 5 A supply | 90 % efficient | 13 W |
| Motion controller, relays, interface | datasheet figures | 10 W |
| Total to cool | as budgeted above |
Drives and most control electronics are rated for 40 C [104 F] ambient unless the datasheet allows more, so hold the inside air at or under 40 C. In a 25 C [77 F] shop that leaves you a 15 K budget, and every 5 K the shop warms takes a third of it away.
What size enclosure does this VFD panel need?
Sealed, about 1.8 m² [2800 in²] of stainless wall to hold 40 C at that load, near a 36 x 30 x 8 box; anything smaller needs a filtered fan indoors or a closed-loop cooler to stay NEMA 4X.
Worked example, sealed stainless. Take a 16 x 16 x 8 in enclosure, rated NEMA 4X / IP66 by the manufacturer and not UL listed. Wall area: front and back 2 x (16 x 16) = 512 in², sides 2 x (16 x 8) = 256 in², top and bottom 256 in², so 1024 in² or 0.66 m². Sealed stainless passes about 3.7 W per m² per K, so this box sheds 3.7 x 0.66 = 2.4 W/K. At that load the inside air sits 100 / 2.4 = 41 K above the room: 66 C [151 F] in a 25 C shop, 26 K over the drive's rating. Sealed passive cooling on a 15 K budget needs 100 / (3.7 x 15) = 1.8 m² of wall, roughly the 36 x 30 x 8 box just quoted.
The same arithmetic settles the small cabinet: a 12 x 12 x 6 in box has 576 in² = 0.37 m², sheds 1.4 W/K, and the drive-included load gives a 73 K rise. With the drive gone, its electronics at 20 W give 20 / 1.4 = 14 K, about 39 C in the same shop and right at the rating.
Forced air changes everything. A fan needs CFM at about 1.76 x watts / allowed rise, which comes from the specific heat of air at 1.2 kJ per m³K. For this load and a 10 K rise that is 18 cfm; choose a 35 cfm free-air fan-filter, and the roughly half that survives the filter still gives you a 7 K rise, 32 C inside. The rating moves with it: a fan-filter assembly sits at about Type 12 / IP54, right for a dust-controlled shop and wrong for a machine that gets hosed. To stay sealed, move the heat through the wall with a closed-loop heat exchanger or an enclosure air conditioner sized for the watts; the cooling comparison of fan, air conditioner and heat exchanger picks one, removing heat from a small sealed IP66 enclosure covers the small end, and the enclosure heat calculation guide holds the full method.
Does the VFD's electrical noise bother the controller in the same box?
No, when the wiring is disciplined: keep drive power wiring 12 in [300 mm] from your analog and encoder runs or behind a grounded barrier, cross at 90 degrees where runs meet, and bond the backplate, drive and enclosure to one ground.
Mount the drive on the metal backplate rather than the door. NEC 250.96(A) requires the metal parts that serve as equipment grounding conductors - enclosures, raceways, backplates - to be bonded together so they carry any fault current imposed on them, and NEC 250.12 requires paint and other coatings removed at the contact surfaces. Run the motor cable as shielded VFD cable with the shield bonded 360 degrees at the drive end, and give it a duct of its own. The servo drive and computer wiring separation article draws the layout. A remote box fixes none of this; bad grounding follows the drive to its new home, and a longer motor cable adds reflected-wave voltage stress at the motor.
What NEMA rating does a VFD enclosure need?
Type 12 with a filtered fan for a dry indoor shop; Type 4X stainless, rated NEMA 4X / IP66 by the manufacturer and not UL listed, once hose water, coolant mist or outdoor weather reaches the machine.
In a dry shop, dust and dripping coolant are the threats, and a Type 12 fan-filter build handles both while it moves the air. When a hose or rain can reach the box, seal it and cool through the wall instead. NEC 110.28 states that IP ratings are not a substitute for enclosure type ratings, so write the NEMA type on your spec; a box marked both Type 4X and IP66 satisfies US and international drawings at once. Grade follows the environment: 304 stainless for the indoor shop and most outdoor sites, 316L where salt air, bleach-based sanitizers or chloride coolants touch the steel. The drive's own manual also names the enclosure classes its electronics are tested for, which caps how harsh its environment can be wherever it lives. Both grades run across the wall-mount enclosure range.
What should you put on the order?
For one box holding the drive and the controls in a dry shop: a 20 x 16 x 8 in, 304 stainless hinged enclosure with about a 35 cfm filtered fan; for washdown, the same size in 316L with a closed-loop cooler rated for the watts.
| Build | Enclosure (H x W x D) | Grade | Cooling | Rating to write |
|---|---|---|---|---|
| Drive and controls, one box, dry shop | 20 x 16 x 8 | 304 | fan-filter, ~35 cfm | Type 12 assembly |
| One box on a washdown machine | 20 x 16 x 8 | 316L | closed-loop cooler, sized for the watts | NEMA 4X / IP66, manufacturer rating |
| Keep the small cabinet | 12 x 12 x 6 in for controller and supply | 304 | none, ~20 W passive | sealed 4X |
| Drive in its own box by the spindle | 20 x 16 x 8 | 304 | fan-filter, ~20 cfm | Type 12 assembly |
The 20 x 16 x 8 box gives 19.9 in of inside height against the 16 in the drive's clearances claim, and 7.9 in of inside depth against a 6 in frame; step to a 10 in deep box if your ducts need the room. Between the catalog steps, a custom enclosure takes your width, height, depth and every cutout, delivered in 10 business days counted from your approval of the drawing, and the enclosure selector narrows the size from what sits inside. Order cable glands rated with the box, IP66 on a sealed build, one per supply, motor and signal entry, and let the fan-filter kit set the assembly's rating at its weakest part.
Decision in one line: one 20 x 16 x 8 box with a fan when the shop is dry; 316L and closed-loop cooling when water flies; the drive alone in its own cooled box when the control cabinet must stay small and sealed.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 16 × 8 in | 304 stainless | 16 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 316L stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 12 × 6 in | 304 stainless | 12 x 12 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How far can the speed reference cable run to a remote VFD?
A shielded 0-10 V pair is good to about 10 m [33 ft]; beyond that, voltage drop and picked-up noise argue for 4-20 mA or the drive's RS-485 port, which runs to hundreds of metres. Route the reference in its own duct, well away from the motor cable, and land its shield at one end.
Can the drive's heatsink go through the enclosure wall?
Yes, several drive makers offer a flange kit that mounts the heatsink fins outside the wall and dumps roughly half the drive's loss outside the box. The kit's gasket keeps the wall sealed, and the whole assembly is rated at its weakest part: the kit's rating if it is lower than the enclosure's.
How many watts can a sealed stainless enclosure shed?
Stainless walls pass about 3.7 W per m² per K, which is roughly 3.4 W per ft² of surface at a 10 K rise. A 16 x 16 x 8 in box carries about 7 ft² of wall, so sealed it holds about 24 W at that 10 K rise - a useful number when you are deciding what stays in a small sealed box.
Does the drive need an input reactor in a shared enclosure?
Placement does not decide it. Add a 3 % impedance input reactor when the motor cable runs past about 50 m [165 ft] or the supply is stiff, meaning a transformer ten times the drive's kVA. Budget the reactor at about 2 % of the drive rating as extra heat, near 30 W for a 2 hp drive, in the same box.
Will a 12 x 12 x 6 in enclosure hold any drive at all?
Only the smallest. The 11.9 in inside height fits a sub-micro frame under 4 in [100 mm] tall once its 4 in clearances top and bottom are counted, and such a drive loses about 10-15 W, which the box sheds at a 7-11 K rise. Anything from 2 hp up needs the bigger box or the remote one.
