Knockout Hole Punch Usage Guide

If you’re wondering what a knockout hole punch is and how to use it correctly, read on.

In this article, I will talk about how to practically” step by step” install your electrical pulling box with a cable trunk or a cable tray using a knockout hole punch.

First of all, you need to know that the cable trunk or tray is primarily used in projects to accommodate various electrical and low-current systems’ wires and cables.

These cables & wires run from the system’s panel to the outlet, whether it is ceiling- or wall-mounted.

So, we shall find a way to connect the outlet box and the cable trunk or tray. That’s why we will use an intermediate backbox that connects directly with the sidewall of the cable trunk or tray.

Usually, we use a galvanized steel backbox (GI box), and its size depends on the number and outer diameters of the cables or wires that pass through it from the cable trunk or tray.

In most cases, we will find that you will use a 10x10cm square GI backbox.

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Why do we need to use the knockout hole punch?

Moreover, the material of the trunking system or tray is mostly manufactured from hot-dip galvanized sheets. Simultaneously, the cable truck’s sidewall or tray height is not less than 5cm and is usually 10 cm.

Hence, to connect the back of the pulling box to the trunk’s sidewall or tray, we need to make a hole in the cable trunk’s sidewall, and this is where the knock-out hole punch tool comes into play.

Please note that there’s an alternative solution for creating a round opening in the steel sheets: use a stainless steel hole saw cutter or a step drill bit. Still, both options can give you an opening with sharp edges, affect the sheets’ galvanization, and not provide an accurate round opening like you get with the knock-out hole punch.

So, we can conclude that the knockout hole punch tool’s function is to cut a clean, round opening in the steel sheets of various electrical items, such as cable trunk or tray, panel boards, pull boxes, and so on.

We have two main types of this tool: the hydraulic and the manual ratchet.

Knockout Hole Punch Manual Ratchet Type - engalaxy.com — **Knockout Hole Punch – Ratchet Type**

Knockout Hole Punch Hydraulic Type - engalaxy.com — **Knockout Hole Punch – Hydraulic Type**

Both of them will perform the same function, but the differences will be in the speed of making the opening, the effort required to make it, and the maximum opening size that can be cut.

But for sure, the more options you get, the more money you will pay. That’s why the hydraulic knock-out hole punch is more expensive than the manual ratchet one.

Now I will start by discussing the manual ratchet-type knockout hole punch tool, step by step.

This Ratchet Type Manual Knockout Hole punch consists of four main parts:

A- A draw stud (it’s a large threaded bolt to make a connection between two pieces, the metal cylinder, and the die).

B- A die, which it’s a metal cylinder.

3- A punch that is responsible for cutting to make a knock-out hole.

4- A ratchet wrench hand, we can rotate it either clockwise or counterclockwise.

Here are the steps which you need to follow to get a round shape opening in your steel sheet:

1- You need to use a drill machine and a cobalt drill bit to make a hole in the steel sheet of your trunk, tray, or panel board.

Note: I highly recommend using a cordless drill machine, as its size is small, which can help you a lot in congested places.

The hole size is to be the same as the diameter of the draw stud. To allow the draw stud to be inserted inside the steel sheet to connect the die and punch.

Usually, the draw studs come in two sizes: 3/8” in diameter (small) and 3/4” (big).

2- Based on your required opening in the steel sheet and the fitting size, which will be connected to the sheet, you will use the proper size of the die.

For example, if we need to connect a backbox to a GI cable trunk, at the same time, we need a hole with a size of 3/4”.

We need to install a brass bush reducing male with a metallic insulated conduit bushing, so we will use a die with a size 3’4” to be connected to the draw stud.

3- Connect the desired size of punch to the draw stud from the other side of the sheet, so now, the draw stud is inserted through a hole in the metal sheet of the tray and connecting between the die from one side of the tray, and the punch on the other side of the tray.

Note: the punch is the piece with the cutting edges, while the die is the piece with the cylindrical flat edges.

4- Connect the ratchet wrench handle to the draw bolt, then rotate the handle. You can see the ratchet hand turning. It pulls the punch towards the die.

You need to keep turning the hand until the punch cuts through the steel.

5- Separate the draw stud and punch, and remove the little ring of waste material lodged inside the die.

It is called a slug and is usually split in half by the punch, earning this punch the nickname “slug-buster.” 😀

How to use the knockout hole punch - engalaxy.com — **How to use the knock out hole punch practically on-site**

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Congratulations, now you can connect the pulling GI backbox with the GI cable truck using the brass bush reducing male with metallic insulated conduit bushing. You are ready to fix from the top side of this pulling backbox an EMT/RGS or any other pipe material to your required final location.