What is the purpose of using conduit elbows, nipples, and couplings?

As strong as all of those 10-foot sections of steel conduit are, they still don't make a complete system without the aid of elbows, nipples, and couplings.

Factory elbows:

Elbows of the correct type and dimensions are an important element of any raceway installation. They're bent sections of conduit or tubing used to change raceway direction or bypass obstructions. IMC and RMC elbows are threaded on both ends.

Factory-made elbows in both standard and special radius are readily available for all sizes of RMC, IMC, and EMT. Elbows with integral couplings are available in trade sizes 2½ through 4. Specialized large radius elbows, which are often referred to as “sweeps,” are also available. They are typically custom-ordered to solve various installation problems. Sweeps are typically used to facilitate easier wire pulls, assist with conduit installs in limited or geometrically difficult spaces, provide specific stub-up length, or enhance protection of communications or fiber optic cables during wire pulls.

Physical dimensions of factory-made elbows for RMC, IMC, and EMT vary between manufacturers. When installing factory elbows for a job, be aware of this variability to avoid installation problems. Always measure to be safe. To order factory elbows you need to specify the raceway type, trade size, and angle of bend. If ordering a special radius elbow, you'll also have to specify the radius.

Nipples:

A nipple is a short length of conduit or tubing material that's used to extend a conduit system. Nipples are used between conduit or tubing and items such as, but not limited to, fittings, boxes, and enclosures or between two boxes, two enclosures, etc. When nipples are used to extend a conduit run to an enclosure, box, etc., the percentage wire fill requirements shown in Chapter 9, Table 1 of the NEC apply.

When a nipple is installed between boxes, enclosures, etc. and it doesn't exceed 24 inches, wire fill is permitted to be 60%. Factory-made RMC nipples are threaded on both ends and are available in all sizes in lengths up to and including 12 inches. Longer lengths are available by special order or may be field-fabricated.

Couplings:

Factory-made couplings for EMT, IMC, and RMC are available in all conduit sizes. Integral couplings are available on trade sizes ½ through 4. On EMT, the coupling is a belled end of the conduit with specific setscrews. For IMC and RMC, the coupling is a separate component that permits joint make-up by turning the outside coupling rather than the conduit.