The questions and answers below are based on the current edition of the NEC®. However, local codes can differ, and your authority having jurisdiction (AHJ) may have opinions that also differ. It is always important to verify your planned installation with the local AHJ.
We’ve been asked several questions about the use of intermediate metal conduit (IMC) at trade shows and other events over the last year and realize there are a lot of misconceptions about IMC. Here are some of the questions we have been asked:
Does IMC offer the same amount of physical protection as RMC?
Yes, the National Electrical Code (NEC) allows both to be used in all applications as IMC offers equivalent physical protection to RMC.
When compared to RMC, does IMC have installation limitations under the NEC?
No, NEC Article 342 states the following under the uses permitted section (342.10), “Use of IMC shall be permitted under all atmospheric conditions and occupancies.” A simple rule to remember for using IMC would be, if you can use rigid steel conduit, you can use IMC.
Is IMC allowed to be used in wet locations?
Yes, According to NEC Section 342.10 (D), IMC can be used in wet locations, but all supports, bolts, straps and screws should be of a corrosion-resistant material. The same requirement applies to RMC.
Can IMC be used for protection of service entry cables?
Yes, IMC can also be used for physical protection of service entrance cables according to NEC Section 230.50(1).
Can IMC be used as a service mast for support of a service drop above a roof?
Yes, according to NEC Section 230.28.
Can you install IMC in a hazardous location?
Yes, NEC Chapter 5 allows threaded steel IMC to be installed in all hazardous locations.
Can IMC be used for an installation in concrete or other corrosive environment?
Yes, IMC can be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection (IMC is provided with corrosion protection per UL-1242) and judged suitable for the condition.
Those are the answers to the most common questions we receive regarding IMC. We would also like to share some other facts about IMC that may be of interest during the selection, installation or inspection of IMC:
- IMC is an excellent equipment grounding conductor and is recognized for use as such in Article 250 of the NEC.
- The coefficient of expansion for IMC and RMC are the same.
- IMC is considered non-combustible by building codes. Therefore, when used to penetrate a fire wall, the International Building Code — in an exception to its main rule — allows the annular space to be filled with common building materials (cement, mortar or grout).
- IMC is Listed to Underwriters Laboratories (UL) Safety Standard 1242, which includes performance-based requirements, including a beam strength test and a threaded conduit pull-out test.
If you still have questions or concerns about using IMC, please contact us.