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Electrical metallic tubing (EMT) is a lightweight conduit that is used to encase electrical wires within a structure. Although there are several other piping materials available, electrical metallic tubing is one of the more common choices by contractors because it is more cost-effective than comparable materials. Steel and aluminum are the two main choices used to make electrical metallic tubing, and in many cases, it is also galvanized with zinc coating so that is will remain resistant to corrosion. Unlike many of the other options within electrical tubing, EMT does not thread together; instead, the ends are fitted to clamps which hold them together.
This tubing is among the most popular choices for both indoor and outdoor use because it is the lightest steel encasement on the market. Since it is constructed from a premium metal, it controls the flow of electricity throughout the pathways that are created, and many regions actually specify that EMT must be used to meet building standards. Nonmetallic tubing is also much more vulnerable to moisture, which definitely has no place around free-flowing electricity. Exposure to chemical vapors or protection from accidental blunt-force impacts are also reasons that EMT is used; even light metallic plating is better than none at all.
Another reason why contractors use electrical metallic tubing over many of the other materials available is the ease of installation. Construction workers often have to function within a very confined space to install electrical tubing, and some of the bulkier alternatives are much more difficult to handle. Within crawlspaces or attics, electrical metallic tubing can be implemented quickly and efficiently, and the threaded clamps interlock for a secure connection. Since EMT is also somewhat flexible, it can be installed throughout other areas that would be otherwise impossible. An additional benefit is that since electrical metallic tubing is often galvanized, it is also suitable for installation it outdoor environments.
Electrical metallic tubing also has its share of drawbacks, and it is not recommended for every possible application. When a large series of wires is used, for example, a contractor may prefer to instead use rigid metal conduit (RMC) or galvanized metal conduit (GMC) to provide superior protection. Areas that require numerous bends and curves may be better-suited with flexible metallic tubing (FMT) or flexible metallic conduit (FMC), since they can be manipulated at almost any angle, yet still remain stable. Residential homes are not often wired with electrical metallic tubing either; it is instead primarily used within commercial buildings.
@irontoenail - For one thing, thickness for thickness, metal will usually provide a better resistance to force than plastic, so it is a better choice for that reason.
For another, I believe that it's extremely unlikely that the metal can be electrified by the wires. How would they fray inside the conduit?
And finally, a metal electrical conduit will help to stop electromagnetic interference with the wires, and stop them from emitting that kind of interference as well.
It is usually considered the best option for most installations, and usually even if the majority of the conduit is plastic, I believe that they coat the sides of them with metal for those reasons.
I'm not an expert on it though, so you might want to take it with a bit of salt.
I don't understand why metallic tubing is better than other materials as an electrical conduit, like say plastic. I would have thought plastic would be more flexible, cheaper and more resistant to water.
I guess I also would have thought that the point of a conduit for electrical wires would be to keep the electricity in the wires as much as possible. Wouldn't having a metal tube encasing them lead to accidents? I mean, if somehow one of the wires frays, surely a metal tube is the last thing you want it to be potentially touching, not when you're going to have to get in there and fix it somehow.
I realize these are a standard installation so I'm missing something, because people who understand how it works obviously keep doing it. But, it just doesn't make sense to me.