Wheatland Tube Company - Page 17

Wheatland TUBE COMPANY DIVISION OF JOHN MANEELY COMPANY

Use of Wheatland Electrical Metallic Tubing in Conformance to the 1990 National Electrical Code

ARTICLE 348-ELECTRICAL METALLIC TUBING

Use (348-1 )-The use of electrical metallic tubing shall be permitted for both exposed and concealed work. Electrical metallic tubing shall not be used: (1) where, during installation or afterward, it will be subject to severe physical damage; (2) where protected from corrosion solely by enamel; (3) in cinder concrete or cinder fill where subject to permanent moisture unless protected on all sides by a layer of noncinder concrete at least 2 inches thick or unless the tubing is at least 18 inches under the fill. Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibility of galvanic action. Exception: Aluminum fittings and enclosures shall be permitted to be used with steel electrical metallic tubing.

Ferrous or nonferrous electrical metallic tubing, elbows, couplings and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences when protected by corrosion protection and judged suitable for the condition.

Wet Locations (348-4)-All supports, bolts, straps, screws, etc., shall be of corrosion-resistant materials or protected against corrosion by corrosion-resistant metals.

Size (348-5)

(a) Minimum. Tubing smaller than ½ inch electrical Trade size shall not be used. Exception No. 1: For under plaster extensions as permitted in Section 344-2. Exception No. 2: For enclosing the leads of motors as permitted in Section 430-145(b).

(b) Maximum. The maximum size of tubing shall be the 4-inch electrical Trade size.

Number of Conductors in Tubing (348-6)-The number of conductors in a single tubing shall not exceed the percentage fill specified in the N.E.C. (See N.E.C. code for specific number of conductors permitted in each tube size.)

Threads (348-7)-Electrical metallic tubing shall not be threaded. Where integral couplings are utilized, such couplings shall be permitted to be factory threaded..

Couplings and Connectors (348-8)- Couplings and connectors used with tubing shall be made up tight. Where buried in masonry or concrete, they shall be concrete-tight type. Where installed in wet location, they shall be the raintight type.

Bends-How Made (348-9)-Bends in the tubing shall be so made that the tubing will not be injured and that the internal diameter of the tubing wilt not be effectively reduced. The radius of the curve of the inner edge of any field bend shall not be less than shown in Table 346-10 (See Page 5 of this brochure.)

Exception: For field bends made with a bending machine designed for the purpose, the minimum radius shall not be less than indicated in the following table.

Table 346-10 Exception Radius of Conduit Bends (Inches)

For SI units: (Radius) one inch = 25.4 millimeters.

Bends-Number in One Run (348-10)- A run of electrical metallic tubing between outlet and outlet, fitting and fitting or outlet and fitting shall not contain more than the equivalent of four quarter bends (360 degrees, total) including those bends located immediately at the outlet or fitting.

Reaming (348-11)-All cut ends of electrical metallic tubing shall be reamed or otherwise finished to remove rough edges.

Supports (348-12)-Electrical metallic tubing shall be installed as a complete system as provided in Article 300 and shall be securely fastened in place at least every 10 feet and within 3 feet of each outlet box, junction box, cabinet or fitting.

Splices and Taps (348-14)-Splices and taps shall be made only in junction boxes, outlet boxes or conduit bodies. See Article 370.

General (348-15)-Electrical metallic tubing shall comply with (a) through (c) below.

(a) Cross Section. The tubing, and elbows and bends for use with the tubing, shall have a circular cross section.

(b) Finish. Tubing shall have such a finish or treatment of outer surfaces as will provide an approved durable means of readily distinguishing it, after installation, from rigid metal conduit.

(c) Connectors. Where the tubing is coupled together by threads, the connector shall be so designed as to prevent bending of the tubing at any part of the thread.