Article 342 Intermediate Metal Conduit Type IMC

I. General





This conduit is a circular metal raceway threadable and designed for the protection and routing of conductors and cable. It can be used as an equipment grounding conductor with its couplings and fittings.


Listing Requirements

IMC, the factory elbows, couplings, and fittings must be listed.

II. Installation


Uses Permitted

Intermediate metal conduit can be used in most places and under most conditions. It can be used in the earth or in corrosive locations if it has corrosion protection. It can be used in cinder fill only if 50 mm (2 in.) of noncinder concrete is in direct contact, the conduit is 450 mm (18 in.) or more under the fill, or there is proper corrosion protection. In wet locations all supports, belts, screws, etc. must be protected against corrosion.


Dissimilar Metals

With the exception of aluminum fittings and enclosures, dissimilar metals in contact must not be used where possible.



The conduit used cannot be smaller than metric designator 16 (trade size ½) or larger than metric designator 103 (trade size 4). See 300.1(C) for metric designators.


Number of Conductors

Refer to Chapter 9, Table 1. Cables can be used if not prohibited by cable articles. Cable cannot exceed fill requirements of Table 1, Chapter 9.


BendsHow Made

The conduit must not be injured. Refer to Table 2, Chapter 9, for the radius of the curve for field bends.


BendsNumber in One Run

The maximum that is permitted is not more than 360° in bends between pull points.


Reaming and Threading

All rough edges must be removed when the conduit is cut. When threaded in the field, a tapered cutting die with a taper of 1 in 16 (¾ in. taper per foot) must be used.


Securing and Supporting

It must be installed as a complete system and fastened and supported as noted in (A) and (B) below.

(A) Securely Fastened. It must be securely fastened within 900 mm (3 ft.) of all boxes, cabinets, conduits, or other conduit terminations. When structural members interfere with this, then the distance can be increased to 1.5 m (5 ft.). If approved, it does not have to be fastened within 900 mm (3 ft.) of a service head above a roof.

(B) Supports. It has to be supported at intervals no longer than 3 m (10 ft.). Table 344.30(B)(2) indicates the spacing of supports for straight runs of conduit with the proper couplings and there is a prevention of the transmission of stresses. Exposed vertical risers can be supported at intervals of 6 m (20 ft.), if the couplings are threaded, firmly supported at top and bottom, and there is no other intermediate support available. Horizontal runs that are supported by framing members not longer than 3 m (10 ft.) apart with supports within 900 mm (3 ft.) of the terminations are permitted.


Couplings and Connectors

Threadless couplings and connectors can be used and should be made tight. Comply with 314.15(A). Running threads cannot be used. Use concrete type in concrete and in wet areas. Do not use threadless couplings and connectors on threaded conduit unless it is listed for that use.



A bushing must be used at the point where the conduit goes into a box, fitting, or other enclosure. This is to protect the wire. An exception is made if protection is provided with the box or fitting.


Splices and Taps

They are permitted only if made in accordance with Section 300.15.




III. Construction Specifications



The conduit must be marked every 1.5 m (5 ft.) with the letter IMC and as required by 110.24.


Standard Lengths

This type of conduit has a standard length of 3 m (10 ft.) with one coupling and both ends threaded. Shorter or longer lengths with or without couplings or threads are permitted.

Article 90 Introduction


Wiring and Protection

Wiring Methods and Materials

Equipment for General Use

Special Occupancies

Special Equipment

Special Conditions


Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size

Annex D. Examples

Annex E. Types of Construction

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Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120 © 2008-2017.
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