Enclosure with no knockouts: punch, not drill

Short answer: an enclosure with no knockouts is the normal condition, not a defect, and the cable entries go in with a knockout punch matched to the fitting. A 1/2 in trade-size hub takes a 7/8 in (0.875 in [22.2 mm]) hole; the drill only makes the small pilot hole that guides the draw stud. Punch the entries before the cabinet is wired, and if the panel is already live, lock out and verify absence of voltage before you put steel through the wall. For a stainless enclosure, or any build with a dozen entries, ordering the holes cut at the factory is the cleaner route: every position and diameter lands on the drawing, and the box arrives deburred.

Why the cabinet ships with no knockouts

A bare wall is deliberate. A current-transformer cabinet, a pull box or a stainless enclosure leaves its wall solid so the installer can put every entry where the conductors actually run, at the size the fitting needs. Knockouts only pay off when the maker knows the cable plan, and on general-purpose cabinets nobody does. Every electrician who terminates in cabinets carries a knockout set for exactly this job, and most prefer a solid wall to a ring of knockouts that sits where the conductors do not. A solid wall also holds the seal until you open it: an outdoor, rain-rated cabinet is only as sealed as its entries, which is where NEMA 3R vs NEMA 4X outdoors draws the line.

The hole each fitting needs

Size the hole to the fitting, not to the cable. UL 50 Table 71-1A sets knockout diameters and fitting dimensions by trade size, and punches are sold against the same numbers: the punch sold for a trade size cuts the hole its hub needs.

Metric glands repeat the pattern with their own nominal holes: M20 cable gland hole sizes lists the usual values for plastic and aluminum walls, and the cord grip hole size chart matches connectors to standard knockouts. The fundamentals behind cutout layout, glands and windows sit in the enclosure cutouts guide.

What you need

• A knockout punch set sized to your entries. Manual kits drive mild steel up to 10 gauge (3.5 mm), the rating typical kit datasheets print. A hydraulic set takes thicker walls and a full day of punching; selecting a hydraulic knockout punch set for control panel work covers the choice.
• A drill with a pilot bit matched to the draw stud; the kit datasheet lists the size.
• A center punch and a marker.
• Cutting oil for the draw stud threads.
• A deburring tool or a round file.
• Zinc-rich touch-up paint when the wall is painted steel.
• The fittings themselves: gasketed threaded hubs or cable glands with locknuts.

Punching the entry, step by step

1. Mark the hole centre from your layout, clear of seams, stiffeners, the door flange and anything mounted behind the wall. Space entries so the dies never overlap; one slug diameter between edges is enough.
2. Center-punch the mark so the drill cannot walk, then drill the pilot hole. The draw stud should pass with light finger pressure; a sloppy pilot lets the punch wander oval.
3. Thread the draw stud through from inside the box and stack the parts: punch against the inside face, wall, die against the outside face. You tighten from outside, where the ratchet has room.
4. Turn the ratchet square to the wall and add a drop of oil to the stud threads every few turns. A tilted die shears an oval hole and piles the burr on one side.
5. Drive until the slug shears through and drops free. Steady resistance ends in a clean cut; chattering means a dull die or a wall past the kit gauge rating.
6. Strip the slug from the die and run a deburring tool around both faces; one turn does it on thin sheet.
7. On painted steel, cover the bare edge with touch-up paint before the fitting goes in. The locknut hides most of the edge, and a wet location finds the rest.
8. Fit the hub or gland with its gasket and locknut and pull it tight. The sealing order that keeps the rating is walked through in installing a cable gland without losing the rating, and the conduit version in field-drilled conduit entries that keep a NEMA 4X rating.

Worked example: a 1/2 in entry in a 14 gauge cabinet wall

The inputs: the fitting is a 1/2 in trade-size threaded hub, so the hole comes from the table above: 7/8 in (0.875 in [22.2 mm]). The wall is 14 gauge (0.075 in [1.9 mm]) steel, the common gauge for a cabinet body in this size class. Treat that gauge as the worked-example assumption and put your own wall gauge in its place. The tool is a manual kit rated for mild steel up to 10 gauge (3.5 mm).

The rule is a thickness comparison in one unit: the wall must sit under the punch rated capacity. The capacity converts as 3.5 mm ÷ 25.4 mm/in = 0.138 in. The load works out as 0.075 in ÷ 0.138 in = 0.54, so the 14 gauge wall draws about 54% of the kit rated thickness. The hole check runs the other way: 0.875 in × 25.4 = 22.2 mm, the slug the die must carry.

Result: the manual kit drives this entry with margin, and the 7/8 in slug is well inside its range. The threshold that follows: keep the manual set for walls at 10 gauge (3.5 mm) or thinner, and step up to a hydraulic set above that. Stainless work-hardens and asks more of a die, so on a stainless enclosure the factory cutout is the reliable route.

Checks when the hole is done

• The slug came out in one piece with a bright shear band; a torn slug means a dull die, and the hole edge will show it.
• The fitting drops in square, with even clearance round the thread.
• The gasket seats on bare metal all the way round, with no gap where the punch tilted.
• The locknut is tight, and the fitting cannot be turned by hand.
• The assembled entry still meets the box rating, which after any cut is set by the weakest part: what a panel keeps after you cut it and mount devices works that rule through.

Mistakes that cost the rating

• A hole saw for the final hole: it burns the coating, tears a burred edge and removes a wide arc of paint that a gasket cannot bridge.
• A big twist drill for the entry: drills past about 1/2 in grab thin sheet and leave a lobed hole. Pilots only.
• An oversize or misplaced hole: a gland gasket bridges a little clearance, not a 1/4 in gap. Cover a spoiled cluster with a small weatherproof box over the cable entries, or hand the wall to the factory.
• A bare hole with no fitting: an open hole ends the seal whatever the label on the door says. Every entry gets its gasketed hub or gland.
• A bare edge on painted steel in a wet location: rust creeps inward from an unpainted edge once moisture sits on it.

Punch on site or order the cutouts

One field entry into an installed cabinet: punch it on site. That is why the wall came bare, and a manual kit with the right die finishes the job between the pilot hole and the locknut. A stainless enclosure, repeated builds, or a dozen entries over three faces: order the holes cut first. Set every position and diameter in the cutout designer, check the spacing on the exported layout, and see what changes against a field hole on the custom stainless enclosure page: deburred edges, no touch-up paint, and the layout documented on the approval drawing. Our stainless boxes are rated NEMA 4X / IP66 by the manufacturer; not UL listed, and custom work is delivered in 10 business days, counted from your approval of the drawing.

So the decision: solid wall and one entry, matched die, punch it; stainless walls or many entries, put the holes on the drawing and let the factory cut them.

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.

Questions