How to Determine the Correct Pipe for Electrical Work
To determine pipe size for electrical work, know what you are using the pipe for. Pipe size varies from home to commercial projects and is determined by what wire or wires you are going to pull through it. Pipe protects wire from corrosion and is a safety precaution for people. Refer to the National Electrical Code book or NEC to determine the type of pipe needed.
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Instructions
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Refer to the NEC, 2008 edition, to understand how to determine the size of the pipe. According to Chapter 9, Table 5, the first column indicates the type THHN or Thermoplastic High Heat Nylon. This is the type of wire you will be using for your project.
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Look at the second column to see your wire size for the project. Common wire sizes are #12 and #10. Locate the approximate area column on Table 5. Write down the number: for #12 wire the number is 0.0133; for #10 it is 0.0211.
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Multiply these numbers by the number of wires you are going to use in the pipe. Example: six wires times .0311 equals .0798, three wires times .0211 equals .0633). Add the two totals together (.0798 plus .0633 equals .1431).
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Refer to the NEC Chapter 9, Table 4, to find electrical metallic tubing. Since we are using more than two wires in the example, use the over 40 percent column in the table. Using the total from the example (.1431), find a number that is close to but less than .1431 in the 40 percent column. Place your ruler below the number that says "trade size." This is the pipe size for the wires you are installing, "¾-inch" pipe.
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Tips & Warnings
The more wires you use, the larger the pipe will need to be.
Use a licensed electrician to wire your home or commercial project. If done incorrectly electrical voltage can be deadly.
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Resources
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