Conduit Fittings and Supports ~ Electrical Knowhow

In Article " Types of Electrical Conduits ", I explained the following points:

Definition of An electrical conduit,
Advantages of using Electrical conduits than other wiring methods,
Disadvantages of using Electrical conduits,
How to Verify Correct Installation of Conduit,
Types of Conduit.

Today, I will explain Conduit Fittings and Supports as follows.

Conduit Fittings and Supports

Types of Conduit Fittings and Supports

There are many types of conduit fittings, made in different sizes and shapes. The type of conduit fitting used will depend upon the particular need. These conduit fittings can be listed as follows:

Conduit bodies and covers
Conduit Bends,
Conduit Coupling,
Conduit Bushing,
Conduit Union,
Reducing washers,
Conduit nipples,
Conduit straps,
Conduit clamps.

1- Conduit Bodies And Covers

Conduit bodies are tubular hardware units with openings at each end to admit EMC conduit and cavities that are large enough to give the installer access to the ends of wires or cables so they can be pulled out and easily be redirected if necessary. (see Figure 1).

These bodies are available in different sizes and are made to perform such functions as joining two sections of conduit to form either straight lengths or 90° bends.

Conduit bodies have threaded ports or openings for conduit and tapped holes for the screws to fasten the covers over the cavities to form watertight seals when wire or cable arrangement is complete.

Conduit bodies are especially useful for making right-angle bends in stiff, heavy conductor bundles or cable such as service entrance (SE) cable. For this reason they are widely used in making service entrance connections.

Conduit bodies are standard commercial hardware items made from malleable iron or copper-free aluminum. The iron bodies can be galvanized or painted with enamel to prevent rusting.

Conduit bodies must be durably and legibly marked with their volumes by the manufacturer to be approved for containing splices, taps, or other devices.

Figure 1. Conduit Bodies And Covers

2- Conduit Bends

Do not damage the tubing or effectively reduce the internal diameter when bending conduit. Use a hand or mechanical bender for sizes up to 1-1/2 inch. Use a hydraulic bender for bends of sizes larger than 1-1/2 inch.

Make sure there are no more than four quarter bends (360 degrees) between pull points per the National Electrical Code. This includes the offsets located next to the box or enclosure.

Ensure that the radius of the curve of the inner edge of any field bend meets the requirements in Table 346-10 of the NEC.

("Double Printing" Pasteup)Factory bends:

It referred to as elbows, are manufactured to a specific angle. They are short lengths of conduit threaded on both ends and commonly made in 90- and 45-degree angles as shown in Figure 2. Factory bends range in size from 1/2 inch to 6 inches.

Figure 2. Factory Bends (Elbows)

3- Conduit Coupling

When two lengths of conduit connect, a coupling joins them. Figure 3 shows a rigid conduit coupling. The coupling is threaded on the inside and made in different sizes.

Figure 3. A Rigid Conduit Coupling

4- Conduit Bushing

A locknut fitting (Figure 4) screws onto conduit connecting it to an enclosure. A bushing (Figure 4) provides protection for conductors leaving the conduit opening.

Figure 4. A Locknut and a Bushing

Figure 5 shows the application of both the locknut and the bushing. Two locknuts connect a piece of conduit to a punched enclosure. The locknuts are tightened on both sides to secure the conduit. The bushing screws on to the end of the conduit and protects the wires from damage as they are pulled through the conduit.

Figure 5. The Application of a Locknut and a Bushing

5- Conduit Union

The conduit union (Figure 6) connects two sections of rigid conduit when neither section can physically turn. The union is a conduit coupling used for emergency repair work and in difficult places near corners, walls, or ceilings. The two types shown are a union with two female hubs (UNF) and a union with a male and female hub (UNY).

Figure 6. Two Types of Rigid Conduit Union

6- Reducing washers

Reducing washers connect smaller diameter conduit to larger boxes and enclosure holes. Threaded reducers connect smaller conduit to larger conduit fittings. Figure 7 shows how a threaded reducer and a reducing washer work.

Figure 7. Reducing Fittings

7- Conduit nipples

Conduit nipples (see Figure 8) protect wiring between two enclosures mounted close together. Nipples are threaded on both ends and vary in size and length. A conduit nipple is specified by Chapter 9 of the NEC, Note 4 to Tables, as having a maximum length of 24 inches. The nipple may be filled to 60% of its total cross-sectional area, and the adjustment factors of Section 310-15(b)(2)(a) need not apply.

If nipples exceed the 24 inch maximum, the system becomes a raceway and only three current-carrying conductors are permitted in a raceway without applying the derating factors. The 40% fill rule would also apply.

Manufactured nipples come in three classifications, the close, short, and long nipple. They vary in length from 1-1/8 in. to 8 inches. Any length beyond 8 inches is made by the installer.

Figure 8. Conduit Nipple

8- Conduit straps

Conduit straps mount against the conduit to fasten it in place (Figure 9). Straps fasten to the wall or ceiling with screws or bolts. Straps are support fitting.

Figure 9. Conduit Straps

9- Conduit clamps

Conduit clamps are used to fasten conduit to fixed structures. They are considered support fittings. See Figure 10.

Figure 10. Conduit Clamps

Notes for Conduit Supporting

Rigid metallic conduit and electrical metallic tubing both require support. Conduit should be fastened by straps to the ceiling or wall, or supported on hangers from the ceiling at least every 10 feet (Figure 11). Conduit should be fastened within 3 feet of a box (5 feet of unbroken lengths are allowed if structural members do not permit fastening within 3 feet).
Rigid conduit installed in straight runs are permitted to use Table 346-12(b)(2).
Liquidtight flexible conduit must be fastened in place by an approved means within 12 inches of each box, cabinet, conduit body, etc. and must be supported and secured at intervals not to exceed 4.5 feet.
There are exceptions to the above rules and these can be located under the various support headings in the individual articles of the Code.