When it comes to knocking out a hole in an electrical box, panel or cabinet, nothing is as efficient as a knockout set. While the overall process has not changed much since its inception, today’s products and styles are streamlined versions of the tools of the past. Before I explore the newer tools in the knockout category, let’s get into some basic components and how the overall process works.

General operation

The basic components for a knockout set are the die (sometimes referred to as the cup), the punch (or cutter) and the draw stud. The die and punch are matched by size: if you are looking to knock out a 1-1/8-in. hole, then you use a 1-1/8-in. die and a 1-1/8-in. punch. Typical sizes range from ½-in. up to 6-in. conduit, and additional sizes are available.

To begin the knockout process, drill a pilot hole into the panel or box at the required location. The size of the knockout determines the size of the pilot hole. Knockouts for ½-in. conduit will require a pilot hole a bit larger than 3/8 in., while everything over the ½-in. size will require a pilot hole of at least ¾ in. Once the pilot hole has been drilled, the die is slid over the draw stud and the stud is inserted into the hole in the panel or box.

The punch is threaded onto the stud up to the point of being in contact with the underside of the panel or box. It is drawn up into the die by turning the draw stud clockwise, piercing the metal box and removing the slug in the process.

Separate from the portion of the knockout doing the actual cutting, a hand wrench or ratchet, hand-operated hydraulic pump or electrically powered hydraulic pump is necessary to draw the punch through the metal and into the die.

Since its release, the Greenlee (Rockford, Ill.) model 7238SB knockout kit with ratchet and Slug Buster has long been the standard. It has everything an electrician needs to punch a ½-in. to 2-in. hole in an electrical panel or box, including a ratcheting wrench.

For electricians on a budget, or who don’t need the full range, there are other products available. Current Tools, Wellford, S.C., offers a budget-friendly knockout set at a much lower price than many other manufacturers. However, the ratcheting wrench is not included with this set, and the range of hole sizes is limited to ½ in. through 1¼ in.

Klein Tools, Lincolnshire, Ill., model 53732SEN knockout punch set is also wallet-friendly. Knockout sizes range from ½ in. to 2 in., and it includes a ratcheting wrench. It can be found at many retail home centers and online, eliminating the need to visit an electrical specialty store.

When making a significant tool investment, individuals often want to purchase one that will cover most of the installations they encounter. Greenlee model 7310SB 11-ton hydraulic knockout kit with hand pump and Slug-Buster is a set that gives tradespeople everything they need. It comes with knockouts from ½ in. through 4 in., the necessary draw studs to match varied die sizes and a manual hydraulic pump to actuate the equipment. The hydraulic pump allows the electrician to cut through thicker material and exert much less effort than a manual wrench. The set also includes a step bit to drill the pilot hole and various spacers for a variety of situations.

New products

Greenlee has been producing knockout sets for close to 100 years, and the company has developed develop several items that streamline the knockout process.

The first is the Slug Splitter punch. While many knockout punches cut around the circumference of the circle, leaving a round hole, they also distort the slug being removed into a flowery shape that can become bound on the draw stud. The Slug Splitter punches add cutting surfaces that bisect the slug during removal, preventing it from impacting the draw stud.

The self-centering Slug Splitter eliminates the possibility of the punch moving during the setup process by placing the inside portion of the cutting teeth to line up with the outside of the pilot hole. This punch also has the slug-splitting capability of previous models. 

The time to thread the cutter on and off the draw stud may be quite lengthy, especially if multiple holes are being installed in a panel or box. With the Speed Punch/Lock system, the need to manually thread the cutting punch onto the stud was eliminated. The threads on the draw stud were removed and a clamshell-type locking system was installed on the end of the stud to keep the cutting punch in place.

Milwaukee Tool, Brookfield, Wis., has also made improvements in the knockout tool realm. The company’s Quick Connect Alignment System makes the draw stud quickly removable from the tool, eliminating the need for the electrician to support the entire weight of the tool while threading on the cutting punch. This results in much easier and more efficient hole installations, especially when doing repetitive punching. It’s also more accurate, since there’s less chance of the punch shifting in the pilot hole.

Milwaukee Tool’s Exact line of punches and dies features large, engraved red crosshairs on the dies, enabling the user to accurately and efficiently align the tool. Another feature of the Exact system are the slug removal ports on the rear of the Exact die enables the tool to remove the slugs so they don’t get wedged in the die. 

Southwire has also entered the knockout tool realm with the MPXD-SD. While most sets rely on a proprietary, built-in source to actuate the knockout, Southwire’s model uses the electrician’s drill to provide the power. Simply drill the pilot hole and thread the cutter onto the draw stud as you normally would, then attach the cordless drill to the unit and begin drawing the cutter into the die. This product employs a tool that’s already in the user’s arsenal, eliminating the need for yet another single-use tool. Another unique feature of this knockout set is something that it lacks. With no hydraulic power source (which tends to leak over time), there’s no mess to clean up.

Additional considerations

There’s even more to take into account when planning which knockout set is right for your application(s). First, consider the material being removed. While many manufacturers offer dies and punches rated to cut mild and stainless steel, not all of them will. A thorough understanding of what your set is rated to cut is crucial to the tool’s performance and longevity.

Another consideration is the power plant driving the die and cutter together. While a ratcheting setup works well for lighter gauge metals or periodic use, knockout sets with hydraulic pumps are better for heavier-gauge metals or frequent use. If using a battery­-powered, cordless tool knockout, a 6-ton tool will punch most size holes in mild steel, making it an excellent choice for general or service type work. A tool in the 10-ton range will make holes in heavier gauge stainless steel, but its size makes it better suited for larger commercial or industrial work.

Finally, consider the battery system. By choosing a knockout set that uses the same battery platform as many (or all) of the current cordless power tools in your inventory, you can cut down on another type of battery to keep track of and maintain.

Conclusion

Although the process has not changed much over the years, several technological advances have transformed knockout tools. The standard hand pump or hand-ratcheting sets are no longer the only options. Users should consider what material you are knocking out, how often you will be using it and how much of an investment you want to make when choosing a knockout set.

Metcalf’s passion for passing on his knowledge has been an integral part of his 30+ year career. In addition to his work as a master electrician, he teaches numerous courses for Electrician U to help equip electricians with the skills they need to excel in their craft. To learn more about Electrician U visit ElectricianU.com.

Photos provided by: greenlee / klein tools / milwaukee tool / southwire