Knockout Punches

A knockout punch cuts clean round holes in sheet metal enclosures, boxes, panels and cabinets so conduit and connectors can be installed. It’s a basic electrician’s tool, but punching into an electrical enclosure can expose live parts, leave sharp edges, throw metal slivers, and crush fingers in hydraulic and ratchet punches. Never punch an enclosure that has live parts inside.

• Electricians
• Controls Technicians
• HVAC & Maintenance

Types of punches

• Manual draw-stud punches use a punch, die and a draw stud (bolt) tightened with a wrench to pull the punch through the metal. A pilot hole is drilled first.
• Ratchet punches turn the bolt with a ratcheting handle, reducing the effort needed.
• Hydraulic knockout punches use a hand pump or battery-powered hydraulic ram to drive the punch, for thicker material and larger holes. See Hydraulic Tools.
• Battery-powered punches use a battery pack to run the hydraulic pump. See Battery Safety.
• Step bits and hole saws are alternatives that cut holes with a drill. See Drills & Impact Drivers.

Main hazards

• Electrical shock and arc flash: punching or drilling into a panel, box or switchgear that contains energized parts can short live conductors to the tool or to ground, causing arc flash and severe injury. See Arc Flash and Electrical Injuries.
• Metal slivers and burrs: the slug and edges are razor sharp, and metal fragments fly. Slivers in an enclosure can short out electrical parts later. See Puncture Wounds.
• Pinch and crush: fingers between the punch, die and the metal or between the ratchet handle and the box. Hydraulic punches can crush with high force.
• Hydraulic oil injection and leaks from hoses, fittings and pumps under high pressure.
• Tool failure: cracked punches, dies and draw studs can break under load and fly.
• Falls and awkward positions when punching overhead or in tight spaces, such as on a ladder or lift. See Ladder Basics.
• Hidden hazards: punching into walls or panels could hit conductors, pipes or components inside, including wires that run behind panels. See Hidden Wiring.

Before you punch

• De-energize and verify. Never punch or drill an enclosure that contains live parts. Lock out and tag out the equipment, test for absence of voltage and ground it where required. See Lockout/Tagout and Absence-of-Voltage Testing.
• Remove components, or work on an empty enclosure. Where possible, punch holes before installing wiring or components. If the enclosure holds equipment, remove the live parts or protect them as the plan requires. Use a barrier to block metal chips from falling into the equipment.
• Plan the layout. Check the knockout size for the conduit and fitting you’ll use, mark the hole center and make sure there is room inside for the die and the draw stud, and for the later conduit connection. Keep holes away from edges and other holes.
• Choose the right punch and die for the hole size, the material and the thickness. Don’t punch material thicker than the tool is rated for, such as stainless steel with a mild-steel punch. Check the tool’s maximum.
• Inspect the tool: look for cracks or chips on the punch and die, a bent or worn draw stud, loose parts and hydraulic leaks. Replace damaged parts. See Tagging Out Damaged Tools.
• Wear PPE: safety glasses (or a face shield), cut-resistant gloves and arc-rated clothing where there is any chance of live parts. See Eye & Face Protection, Hand Protection and Arc Flash PPE Categories.

Punching safely

• Drill the pilot hole of the size the punch maker specifies, and deburr it. A hole that is too small makes the punch bind, too big makes it wander. Use a drill bit sharp and the right type for the metal.
• Assemble the punch correctly: place the die on the outside, the punch on the inside as directed, thread the draw stud through the pilot hole and make sure the parts are aligned and seated. Use a drop of oil on the threads.
• Keep your fingers away from the punch, die and draw stud, and keep your free hand off the enclosure edge while pressing. Brace the box with your body and keep your balance.
• Turn or pump slowly and steadily. Stop if the tool binds, bends or makes unusual sounds, and check alignment. Don’t force it with extensions or cheater bars on the wrench.
• Expect a snap when the slug breaks free. The slug can fly out, so keep your face and others away.
• Hydraulic punches: keep hoses and fittings in good condition, release pressure fully before disconnecting and never put fingers over a leak. See Hydraulic Hazards.
• Deburr the hole with a file or reamer. Remove all slugs, chips and metal dust from the enclosure with a magnet or vacuum before closing it up. Don’t blow chips with compressed air in electrical enclosures.
• Install fittings and bushings and seal unused holes with knockout seals or plugs listed for the box, to keep out dust and animals and preserve enclosure ratings. See Hazardous Locations for special enclosures.

Working in the field

• Don’t punch holes in panels or enclosures energized by another source, such as a control voltage or backfeed, without checking. Panels can have multiple sources.
• When modifying an existing panel, check the manufacturer’s listing, which may limit where holes can be made. Listed enclosures can lose ratings if holes are added in the wrong places. See Listed & Labeled Equipment.
• Keep the work area free of metal chips, and clean floors that become slippery from oil.
• Charge and store batteries properly for battery-powered tools. See Battery Safety.

Knockout punch checklist

• The enclosure is de-energized, locked out and tested; no live parts are inside
• I chose the right punch and die, and inspected the tool for cracks and wear
• I drilled and deburred a correct pilot hole
• I wear safety glasses, gloves and arc-rated clothing when needed, and keep fingers clear of the punch
• I removed all slugs and chips from the enclosure and deburred the hole
• Unused openings are sealed with listed plugs

Last updated: October 5, 2026