Section 342.10/Uses Permitted for Intermediate Metal Conduit (IMC)
NEC 342.10 lists the conditions and locations where intermediate metal conduit (IMC) is permitted as a wiring method.
Intermediate metal conduit (IMC) is permitted in all atmospheric conditions and occupancies. Section 342.10 allows IMC in exposed and concealed locations, in concrete, in direct burial (when protected by corrosion protection suitable for the condition), in or under cinder fill (with corrosion protection), in wet locations, and in dry locations. IMC is a thinner-wall steel conduit compared to rigid metal conduit (RMC) per Article 344, providing similar physical protection with less weight and easier installation. IMC uses the same threading, fittings, and supports as RMC. Trade sizes range from 1/2 inch through 4 inches. IMC provides an equipment grounding path per Section 250.118 and is accepted as a grounding conductor where properly installed with listed fittings.
Why this section exists
Metal conduit wiring methods provide physical protection for conductors and a reliable equipment grounding path. The NEC organizes conduit types by wall thickness and material: RMC (heaviest), IMC (intermediate), and EMT (thinnest). IMC fills the gap between the heavy-duty protection of RMC and the lighter protection of EMT (Article 358). The uses-permitted sections are critical because specifying a conduit type in a location where it is not permitted is a code violation. Plan reviewers cross-reference the specified conduit type against the installation conditions (exposed, concealed, wet, corrosive, hazardous, direct burial) to verify compliance.
What plan reviewers look for
Plan reviewers check the conduit schedule and electrical drawings for the specified wiring method at each location. They verify that IMC is appropriate for the installation conditions: exposed runs in parking garages, concealed runs in walls, underground runs to exterior equipment, and embedded runs in concrete slabs. They check that corrosion protection is specified for direct burial and cinder fill applications. They verify that fittings are listed for IMC (not generic compression fittings intended for EMT). For installations accessible to unqualified persons, they check that the conduit provides adequate physical protection.