Despite popular misuse of the term, conduit does not include electrical metallic tubing. Chapter 3 covers two types of non-flexible metallic conduit:
- Intermediate metallic conduit (IMC) [342]
- Rigid metallic conduit (RMC) [344]
Both are fairly thick-walled and use threaded fittings. To bend either one on a conduit bender, you must use a shoe rated for conduit. If you use a tubing shoe instead, you will likely damage the shoe. Sometimes, the damage is a crack (shoe must be replaced) and sometimes the shoe shatters; this depends on the mismatch and on how much force you are applying.
The two flexible metallic conduits don’t require a bender, but they also use threaded fittings:
- Flexible metallic conduit (FMC) [348]
- Liquidtight flexible metallic conduit (LFMC) [350]
There are also several non-metallic conduits. One way in which conduits resemble water pipe is they are watertight when assembled correctly. This is why RMC and IMC installations are often installed with a drain and purge in applications where condensation is expected. And it’s why they are installed in applications where water intrusion must be prevented.
Tubing
Chapter 3 covers two types of metallic tubing:
- Electrical metallic tubing (EMT) [358]
- Flexible electrical metallic tubing (FEMT) [360]
These are joined with pressure connectors; you turn screws in a collar to fasten two pieces of EMT or FEMT together. You don’t thread EMT or FEMT, which means saving a series of steps when running this type of raceway. You can bend EMT on a conduit bender, but make sure the shoe says EMT on it. If you use an EMT shoe, remove it from the bender when you are done so the next person doesn’t encounter a safety hazard by trying to bend RMC on it.
Unlike conduit, EMT and FEMT are open at the joints between two pieces. This has implications for wet locations and hazardous locations. For example, in Class I locations (whether Class I or Class 2) you can use IMC or RMC [501.10]. Nowhere is EMT mentioned as a permitted wiring method. Why? Because the raceway needs to be closed rather than open at the joints.
There are also several types of non-metallic tubing. Don’t default to the idea that metallic is stronger than non-metallic and, thus, always preferable. EMT is an excellent choice for many applications [358.10]; sometimes a non-metallic tubing is an even better choice. And sometimes when choosing between the two, EMT is a hands-down winner.
For example, if you want your raceway to be part of the equipment grounding conductor (EGC), EMT and FEMT are the only choices among tubing types [250.118]. Some argue that because of its being open at the joints, EMT isn’t a good choice for an EGC. However, this ignores the skin effect and the fact that when properly secured, the EMT connector makes a solid electrical connection. It is actually a better EGC than a conductor run inside a non-metallic tubing.
So, while “They know what I mean” might seem like an excuse for confusing EMT with conduit, the results can range from destroying the only EMT bending shoe you had on the truck to making a crater where once there was a coal-handling yard.
