Article 344 Rigid Metal Conduit: Type RMC
Rigid Metal Conduit (RMC). A threadable raceway of circular cross section designed for the physical protection and routing of conductors and cables and for use as an equipment grounding conductor when installed with its integral or associated coupling and appropriate fittings.
Informational Note: See 300.6 for protection against corrosion.
Exception: For enclosing the leads of motors as permitted in 430.245(B).
Informational Note: See 300.1(C) for the metric designators and trade sizes. These are for identification purposes only and do not relate to actual dimensions.
Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.
Informational Note: See ANSI/ASME Bl.20.1-2013, Standard for Pipe Threads, General Purpose (Inch).
- RMC shall be securely fastened within 900 mm (3 ft) of each outlet box, junction box, device box, cabinet, conduit body, or other conduit termination.
- Fastening shall be permitted to be increased to a distance of 1.5 m (5 ft) where structural members do not readily permit fastening within 900 mm (3 ft).
- Where approved, conduit shall not be required to be securely fastened within 900 mm (3 ft) of the service head for above-the-roof termination of a mast.
- Conduit shall be supported at intervals not exceeding 3 m (10 ft).
- The distance between supports for straight runs of conduit shall be permitted in accordance with Table 344.30(B)(2), provided the conduit is made up with threaded couplings and supports that prevent transmission of stresses to termination where conduit is deflected between supports.
- Exposed vertical risers from industrial machinery or fixed equipment shall be permitted to be supported at intervals not exceeding 6 m (20 ft) if the conduit is made up with threaded couplings, the conduit is supported and securely fastened at the top and bottom of the riser, and no other means of intermediate support is readily available.
- Horizontal runs of RMC supported by openings through framing members at intervals not exceeding 3 m (10 ft) and securely fastened within 900 mm (3 ft) of termination points shall be permitted.
Table 344.30(B)(2) Supports for Rigid Metal Conduit
|Conduit Size||Maximum Distance Between Rigid Metal Conduit Supports|
|Metric Designator||Trade Size||m||ft|
|78 and larger||3 and larger||6.1||20|
Informational Note: See 300.4(G) for the protection of conductors sizes 4 AWG and larger at bushings.
- Steel with protective coatings
- Red brass
- Stainless steel