Working with EMT Conduit: Cutting and Measurement
Written by Dave Harris, trueCABLE Technical Specialist, BICSI INST1 Certified
We receive many questions about the installation of our cable products. At times, it is appropriate to suggest to customers that they make use of conduit. Conduit is a building material which is usually in the form of tubing. That tubing is assembled to provide a protected pathway and support system for the installation of wire and cable. At the same time, EMT conduit provides a handy shield in addition to supporting your cable. Most of the time, use of metallic conduit alone negates any need for shielded Ethernet cable which greatly reduces installation costs, effort, and complexity.
Types of Conduit
Conduit is made from steel, aluminum, various types of plastic, and even fired clay. For the installation of low voltage communications cable, there are two types in general use: Polyvinyl Chloride (PVC) and Electrical Metallic Tubing (EMT). PVC conduit is relatively easy to install, but its combustion products make it unsuitable for indoor use. This series of articles will focus on the use of EMT conduit, specifically for the installation of low voltage communications cable.
Please Proceed with Care
This article is for beginners. Generally speaking, working with conduit is not. Installation details for EMT conduit are specified in the US National Electrical Code (NEC). This code, and any additional local codes apply whether your conduit is for low-voltage communications cable or not. As you might expect, the code will not be included in the article. You’ll have to go to the National Fire Protection Association for that.
Conduit in new construction is always installed by trained and licensed professionals. When installed properly, EMT conduit is part of a building’s grounding infrastructure, and is actually a functional part of the electrical system. This article will never prepare anyone to open, add to, repair or otherwise tamper with an existing electrical installation involving conduit. Please don’t do that, or I will have to stop writing this stuff.
So why even have this article? Our goal is to arm our customers with information that will be useful when deploying our low voltage communications cable. We realize that this can only be done if we also stress that there are some extremely important boundaries that need to be recognized. These boundaries are in place for the safety of yourself and everyone else.
About EMT Conduit
EMT is available in standard diameters, known as “trade sizes” that roughly correspond to the inner diameter of the tubing in inches. Common trade sizes are ½, ¾, 1, 1-1/4, 1-½, 2, and larger. Trade size ½ is too small to be useful for Ethernet and coaxial cable. In most commercial communications installations, 1” conduit is the smallest size used. The size(s) of conduit used is an important decision that depends on the specifics of a particular installation. More information about metallic conduit and trade sizes is available in our Cable Academy blog article, “Conduit Fill Chart for Ethernet and Coaxial Cable”.
Figure 1. This is what EMT looks like at the store.
Common trade sizes of EMT are available in lengths of ten feet, sometimes referred to as “sticks.”. EMT conduit, commonly called “thin-wall,” cannot be threaded like thicker versions of steel conduit, so it makes use of coupling and connecting hardware for assembly. We’re starting at the beginning, so it has to be said that EMT must first be cut to length before it can be installed. Cutting to length is a straightforward process: measure, cut, and dress.
You should put on your safety glasses before you even leave for the store, and so should everyone around you. Carrying around a stick of thin-wall conduit is like carrying around a sharpened spear, so even a hard hat is not a bad idea. Once metal-cutting starts, eyewear becomes extremely critical for everyone in the area.
Gloves will both improve your grip and protect your skin. I like using cut level-1 or cut level-2 gloves to optimize dexterity and protect from small skin injuries.
This article is not going to try to teach you how to measure length with a ruler. However, there might be a few points that are worthwhile to consider. Use a steel tape measure. Make sure that the tape measure is at least ten feet long. The hook on the end of the tape measure, along with the rigidity imparted by the curved shape of the tape make it possible for measuring and marking the needed length to be a one person job.
Figure 2. Steel measuring tape. Image courtesy of Milwaukee.
If possible, clamp the conduit to your work surface. Using the hook to hold one end of the tape measure to the end of the tubing, extend the tape past the length you need to cut. Use a permanent ink marker for visibility and durability, and place a small mark on the tubing at the correct length indicated by the tape measure. But don’t stop there. Using the tape measure each time, place several more marks around the circumference of the conduit at the correct length. This will enable you to see the mark even if the conduit is rotated. It also helps to ensure that the freshly-cut end of the conduit is straight and square.
The most common tool used for cutting EMT conduit is called a hacksaw. It is a manually-operated saw with a fine-toothed blade for cutting metal. The cleanest cuts will be obtained using a blade with 32 teeth per inch (TPI), but any hacksaw in good condition will work.
Figure 4. Hacksaw. Image courtesy of Craftsman.
When you clamp the conduit to your work surface, position your length mark off the edge of the surface. Place the saw blade on the mark, and slowly draw the blade across the conduit. Go slow at first, because the blade will tend to wander until a groove starts to appear in the metal surface. Once the blade can be confined to the groove, you can speed up. Use the additional marks on the conduit to maintain a straight and square path through the conduit. Be patient; it can take a few minutes to get all the way through a piece of steel pipe using a hand saw, but you'll get there.
No matter which saw you use, the cutting process will result in a new end that is rough, with imperfections that include sharp edges. These imperfections must be removed in order to avoid damage to the cable to be installed, or physical injury to other people who are to handle your work. So the new end of the conduit should always be cleaned up or “dressed.”
Figure 8. Extreme close up of the smooth end on a new piece of EMT
Figure 9. Extreme close up of the end of a newly-cut piece of EMT. Note the brand new sharp edges on the inside and outside of the tube.
The metal can be smoothed by working it with a file, but flat files are difficult to use on the insides of smaller sizes of conduit. Alternatively, many people use the jaws of slip-joint pliers to file the outside of the conduit end. Just close the jaws around the conduit and rotate the pliers relative to the conduit to file off the cut end. For the inside surface, insert the nose of the pliers into the conduit and rotate to file all the junk off of the inside. Now the end of your conduit can slide into couplers and connectors cleanly and smoothly, and the cable will be protected.
So that’s about it for measuring and cutting EMT conduit. For most people, it’s not a particularly challenging task, but maybe we’ve included a tip or trick that might make preparation of conduit a little easier and more precise. Even if you are never going to install conduit yourself, it’s useful to be able to recognize when it’s done correctly.
This is just a start. There’s much more to follow. If you liked this article, check out our Cable Academy for more like it. And watch out for more in the series, “Working with EMT Conduit.”
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