Opening the knockouts on a NEMA 4X drive enclosure is simple once you know the trick: the molded or stainless knockout rarely pops from pushing, because it is a partially sheared disk backed by a plate. Pull the backing plate off, lever the disk out from the inside, then close the hole with a fitting rated for the same conditions the enclosure is. This article covers the knockout itself, the fitting choices, and the clearance checks that decide whether the wiring actually fits.
Why pushing does not work
Most knockouts in drive housings are stamped or molded with a cut that goes most of the way through. The remaining web holds the disk in place until it is levered. Pushing with a thumb or the back of a screwdriver only bows the disk, which is why it feels immovable.
On molded plastic housings there is often a metal plate staked behind the plastic knockout. Remove the plate first. Then the plastic disk comes out clean with a sharp tap rather than hard force.
Popping a knockout without damage
Work from the inside and use a lever, not a hammer blow on bare plastic.
- Disconnect power and open the drive enclosure so you can see the inside of the knockout area.
- Remove the backing plate or bracket behind the knockout; on many housings it is staked or clipped and pulls off by hand.
- Put the tip of a flat screwdriver in the pre-cut ring, from the inside.
- Strike the screwdriver handle sharply with pliers or an 8 to 12 oz (225 to 350 g) hammer. The disk should bend inward at the cut.
- If it only bends, move the tip a little way around the ring and repeat until the disk is loose enough to grab.
- Twist the disk out with pliers and deburr the edge so a gasket can sit flat.
A bent disk that will not break free means the shear was partial; repeat around the ring rather than prying harder. Prying hard from the outside distorts the surrounding wall, and a distorted wall stops a gasket from sealing.
Choosing the fitting that keeps the rating
The knockout diameter is only half the job. The fitting you put in it is what the rating rests on, and the rating only survives if every part of the assembly is rated for the same conditions.
- Liquid-tight conduit hub for liquid-tight flexible metal conduit to a motor, a disconnect or a control station. The gasketed nut compresses against the enclosure wall on the outside.
- Liquid-tight cord grip for flexible cord, SJ or SO cord. It clamps the jacket, which is what actually stops water wicking along the cable. A cord grip sized for the jacket, not the conductors, is the one that keeps the seal.
- Threaded plug for any knockout you do not use. A dry, open knockout is a straight hole into the panel.
Knockout spacing on drive housings usually follows trade sizes, so standard NEMA-style fittings thread in. But the diameter of the hole is not the whole story: the depth of the plastic or stainless around it may be too shallow for a long straight-thread fitting to seat. Test-fit before you commit to a fitting style. If the knockout is a molded part and the housing thickness is unusual, a cord grip with a long body and a short thread is often easier to seat than a deep hub.
A gland installed correctly, with the hole sized to the sealing ring and the clamp torqued down, is the same principle whether the cable is power, control or a network drop.
Clearance: the check that decides the layout
Inside a drive housing, terminal clearance is often tighter than outside. Measure before you pick a fitting.
- Terminal strip depth. A straight-thread hub projects inward 0.75 to 1.25 in (19 to 32 mm); a low-profile fitting projects less. Compare that to the space between the terminal and the housing wall.
- Bending room. Large conductors need bending space at their terminals; NEC 312.6 sets it for cabinets and cutout boxes. A 10 AWG or larger feeder into a tight corner needs more room than the knockout position suggests.
- Torque access. The fitting's locknut has to be reachable from inside to be tightened. If the drive's own mounting feet or a din rail block the nut, the fitting cannot be seated.
- Dust or liquid exposure. If the drive sits in a washdown or dusty area, the fitting and cord grip both need the rating to match the enclosure, not just the hole.
If the housing's own knockouts are in the wrong place or too tight, a purpose-built stainless enclosure with cutouts placed where the drive terminals actually are is a cleaner path than forcing a fitting into a molded hole.
When a molded housing is the wrong starting point
A drive's own NEMA 4X plastic shell is fine for a bench install in a clean corner. For a real washdown or outdoor build, the drive usually goes inside a larger stainless enclosure. That changes the entry problem completely: the enclosure is yours to specify, and the knockouts become planned cutouts.
Size the inner volume first, then place the entries. Drive enclosure rating, size and cooling for one drive walks through the sizing. The cutout designer lets you draw each hole, hub and gland position on the face you want and sends the layout with the quote, so the entries land where the conduit actually runs.
On a custom stainless body, entries are usually factory-cut rather than field-punched, which keeps the wall flat and the gasket seat true. Whether entries are punched on site or cut at the factory, what matters is that each entry is closed with a rated fitting.
Checks before you button it up
- Every knockout is either fitted or plugged; no dry holes.
- Cord grips clamp the jacket, not the insulation.
- Locknuts are torqued and gaskets sit flat, no twists.
- Conductors have bending room at the terminals and nothing pinches when the cover closes.
- The drive's own cover gasket is undamaged after wiring.
Mistakes that cost the rating
- Prying the knockout from the outside and bowing the wall, so the gasket never seats flat.
- Using a standard (non-liquid-tight) fitting because the thread fits the hole.
- Oversizing a cord grip's hole to suit a bigger cable, leaving the clamp loose on a smaller jacket.
- Forgetting the unused knockout, or closing it with a plug that is not rated for the location.
- Cutting a new hole with a hole saw and not deburring the inside edge, which chews the gasket on the first hose-down.
What to put on the order
If the drive housing's knockouts work, the order is just fittings: liquid-tight hubs for conduit, gasketed cord grips for cord, and plugs for the rest, all sized to the knockout and rated for the site. If they do not, the enclosure is a custom stainless build instead. Specify the material, the size, and the exact entries: the custom enclosure builder takes your width, height, depth and cutouts from one piece, and it is delivered in 10 business days from drawing approval. Ratings are manufacturer ratings for the specified design, not UL listed; that is worth stating on the drawing so nobody downstream assumes otherwise.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| 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 |
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I just drill a knockout instead of punching it out?
You can, but a drill walks on thin sheet and the hole rarely ends up round. A step bit in a slow drill works if the knockout is already open at the edge. On a stainless enclosure you plan to keep, order the entry as a factory cutout instead; the hole arrives sized for your hub or gland with a smooth, sealed edge.
Do cord grips keep a NEMA 4X rating on a drive enclosure?
A cord grip rated IP68 or type 4X by its manufacturer, tightened to the right torque on a hole the right diameter and clamped on the cable jacket, keeps the rating. The weak points are a loose clamping ring on an undersized cable and a rough, oversized hole. A rating after field mounting always depends on the weakest part in the entry, so check each fitting's own rating too.
Why won't my knockout pop out when I push it?
Most knockouts are only partially sheared and are meant to be levered, not pushed. Pull the backing plate off the inside, put a screwdriver tip in the cut, and strike it with pliers or a small hammer. If it bends without breaking free, move the tip around the ring and repeat until you can grab the disk and twist it out.
Does the enclosure keep its rating if the drive manufacturer's knockouts are used?
Yes, when the knockouts are closed with fittings rated for the same conditions and the gaskets compress properly. The rating is judged on the finished assembly, so one dry, untightened hub is enough to lose it. If you cut new openings, treat it as a modification and check what the panel keeps afterwards before you assume the original rating still applies.
