Use of Wheatland Rigid Steel Conduit in Conformance to the
1990 National Electrical Code
Though the National Electrical Code deals primarily with proper field application, it
presumes that the conduit meets the standards necessary to perform properly under approved
conditions. Wheatland rigid steel conduit is made to provide all the qualities
required for proper installation as specified in the Code.
For your convenience in designing and specifying raceway systems of rigid steel
conduit, the applicable articles from the National Electrical Code are enumerated below.
ARTICLE 346-RIGID METAL CONDUIT
Use (346-1 )-The use of rigid metal conduit shall be
permitted under all atmospheric conditions and occupancies subject to the following:
(a)
Protected by Enamel. Ferrous raceways and fittings
protected from corrosion solely by enamel shall be permitted only indoors and in
occupancies not subject to severe corrosive influences.
(b)
Dissimilar Metals. 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 rigid metal conduit, and also, steel fittings
and enclosures shall be permitted to be used with aluminum rigid metal conduit.
(c)
Corrosion Protection. Ferrous or nonferrous metal conduit,
elbows, couplings and fittings shall be permitted to be installed in concrete, indirect
contact with the earth, or in areas subject to severe corrosive influences where protected
by corrosion protection and judged suitable for the condition.
Cinder Fill (346-3)-Conduit shall not be used in or under
cinder fill where subject to permanent moisture. Exception No. 1: Where of
corrosion-resistant material suitable for the purpose. Exception No. 2: Where
protected on all sides by a layer of non-cinder concrete at least 2 inches
thick. Exception No. 3: Where the conduit is at least 18 inches under the fill.
Wet Locations (346-4)-All supports, bolts, straps, etc. shall
be of corrosion-resistant materials or protected against corrosion by corrosion-resistant
materials.
Minimum Size (346-5)
-Conduit smaller than ½ inch electrical trade
size shall not be used. Exception No. 1: For underplaster extensions as permitted
in Section 344-2. Exception
No. 2: For enclosing the leads of motors as permitted in Section 430- 145 (b)
Number of Conductors in Conduit (346-6)-The number of
conductors permitted in a single conduit shall not exceed the percentage fill specified in
the N.E.C. (See N.E.C. Code for
the number of conductors permitted in each conduit trade size.)
Reaming and Threading (346-7)-
(a) Reamed. All cut ends of conduits shall be reamed or otherwise finished to
remove rough edges.
(b)
Threaded. Where conduit is threaded in the field, a standard
conduit cutting die with a 3/4-inch (19-mm) taper per foot (305mm) shall be used.
Bushings (346-8)-Where a conduit enters a box or other fitting, a bushing shall
be provided to protect the wire from abrasion unless the design of the box or fitting is
such as to afford equivalent protection.
Couplings and Connectors (346-9)-
(b) Running Threads. Running threads shall not be used on conduit for
connection at couplings.
Bends-How Made (346-10)-Bends of rigid metal conduit shall be so made that the
conduit will not be injured and that the internal diameter of the conduit will 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.
