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A common misuse of terminology is to call all raceway “conduit.” But conduit is just one kind of raceway. EMT is another kind.
Conduit is really a kind of pipe. You assemble most types of conduit by threading it and screwing threaded connectors onto the threaded conduit. There are some exceptions; for example, you can fuse HDPE conduit together.
EMT is a kind of tubing. In fact, the letters stand for Electrical Metallic Tubing. You don’t thread it; you assemble it with compression connectors.
Two other kinds of tubing are approved for electrical use:
In Chapter 3 of the NEC, you will see a string of articles each devoted to a particular wiring method.
For each of these, the NEC lists “Uses Permitted” in Section 10 of the article, and “Uses Not Permitted” in Section 12.
Nobody will blink if you order Type RMC (rigid metal conduit) for use in a hazardous location. But the NEC imposes severe restrictions on using EMT in hazardous locations [358.2, 504.20]. Take a look at a wrench-tight RMC connection and then look at a properly tightened EMT compression connection. You’ll understand why RMC isn’t restricted and EMT is.
EMT offers some advantages, but it’s not conduit.
Source: Mark Lamendola | Mindconnection