1. What are the differences between electrical metallic tubing (EMT), steel rigid metal conduit (RMC), and intermediate metal conduit (IMC)?
Answer : Guidelines for Installing Steel Conduit/Tubing General Product Information at www.steelconduit.org

2. What National Electrical Code? (NEC®) Articles cover IMC, RMC, and EMT?
Answer: IMC NEC® Article 342 (345); RMC NEC® Article 344 (346); EMT NEC® Article 358 (348)

3. Can RMC, IMC and EMT be direct-buried?
Answer: The 2005 National Electrical Code (NEC) allows the direct burial of all three products as noted in their respective Articles:
RMC Section 344.10 (B) Corrosion Environments. "RMC, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition."
IMC Section 342.10 (B) Corrosion Environments. "IMC, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition."
EMT Section 358.10 (B) Corrosion Protection. "Ferrous or nonferrous EMT, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition."
RMC, IMC and EMT are all "protected by corrosion protection" due to the zinc coating that is applied during the manufacturing process. However, in severe corrosive environments, the designer or AHJ may decide to require additional or supplementary protection.
Underwriters Laboratories' Electrical Construction Equipment Directory contains information relating to limitations or special conditions applying to products listed by UL. The Directory states that RMC and IMC do not generally require supplementary corrosion protection when installed in soil unless: 1. Soil resistively is less than 2000 ohm-centimeters. 2. Local experience has confirmed that the soil is extremely corrosive.
(Note: Soils producing severe corrosive effects have low electrical resistively, expressed in ohm-centimeters. Local electric utilities commonly measure the resistively of soils. The authority having jurisdiction (AHJ) has the authority to determine the necessity for additional protection.)
EMT in direct contact with the soil generally requires supplementary corrosion protection. However, local experience in some areas of the country has shown this to be unnecessary.

4. Do RMC, IMC and EMT comply with the requirements of NFPA 130?
Answer: The requirements for conduit are in section 2.4 and state that materials must conform to requirements of NFPA 70 (NEC) and "shall be capable of being subjected to temperatures up to 932°F (500°C) for 1 hour and shall not support combustion under the same temperature condition."
Galvanized steel conduit and tubing meet this requirement. The product standards do not include tests for the above conditions. However, RMC, IMC and EMT have been exposed at Underwriters Laboratories to the E119 Time-Temperature Curve in a fire of up to four hours in duration. (file NC546 Project 90NK111650"Annular Space Protection of Openings created by Penetrations of Tubular Steel Conduit"). That temperature reached almost 2000°F. The conduit was still intact at the end of the test. Conduit manufacturers cannot verify the condition of the insulation of the conductors within the conduit when subjected to that temperature.

5. Does IMC provide as much physical protection as rigid?

Answer: Yes, even though IMC is lighter and has a thinner wall thickness than rigid, it is just as strong. This is achieved through the steel processing during manufacturing. NEC® Articles 342 (formerly article 345) for Intermediate Metal Conduit and 344 (formerly article 346) for Rigid Metal Conduit contain identical installation requirements. Both products are UL listed and have been tested under similar conditions. 6. What type of threads are cut on RMC and IMC? Answer: The NEC requires that the threads of both RMC and IMC be cut with a 3/4 inch taper per foot (1 in 16) per ANSI/ASME B.1.20.1 Standards for Pipe Threads, General Purpose (Inch). This applies to both factory and field threads.This is the same taper as standard plumbing pipe.

7. How can field-cut threads be protected against corrosion?
Answer: Factory cut threads have corrosion protection applied at the factory. Field cut threads are required to be coated "with an approved electrically conductive, corrosion-resistant compound "where corrosion protection is necessary " (see NEC® 2005 300.6 (A). We recommend that all field cut threads be protected against corrosion where they will be installed in wet or outdoor locations. The thread surface should be protected with conductive rust resistant coating. Zinc-rich paint is a typical coating, but there are other conductive coatings that can be used.
Field threads should be cut one thread short. This will insure a good connection and allow the entire thread surface to be inside the coupling.

8. Is rigid steel conduit the same as schedule 40 pipe?
Answer: The term "schedule 40" originated when ASTM A120 existed and conduit was made from this pipe. A120 was cancelled many years ago. Steel conduit is not required to meet ASTM standards. For any future information, contact steel conduit manufacturers.

9. Can EMT be used over 600 volts?
Answer: Underwriters Laboratories Electrical Construction Equipment Directory states that EMT is listed for "installation of conductors in circuits rated above or below 600V, nominal, and in accordance with an ANSI/NFPA 70, National Electrical Code".
Part II of Article 300 (Wiring Methods) of the National Electrical Code® covers "Requirements for Over 600 Volts, Nominal". In Section 300.37 of Part II entitled "Aboveground Wiring Methods", EMT is listed as one of the permitted wiring methods.
In 1996 Underwriters Laboratories published a report of research entitled Electrical Metallic Tubing for use over 600 Volts.

10. Can steel conduit/tubing be used as equipment grounding conductors or do you have to use a supplementary conductor?
Answer: Yes, RMC, IMC and EMT are all permitted as an equipment grounding conductor in accordance with NEC® 250.118. It is permitted to add a supplementary equipment grounding conductor sized in accordance with NEC® 250.122. This is a systems design consideration. If a supplementary equipment grounding conductor is used, it is still very important to comply with NEC® 300.10 and 300.12, since approximately 90% to 95% of the current will flow on the conduit and not in a supplementary conductor.

11. What are the advantages of using steel conduit (RMC & IMC)/tubing (EMT)?
Answer: Steel conduit and tubing offers several advantages over alternative wiring methods:
— EMI Shielding
— Physical protection of conductors
— Proven grounding capabilities
— Low coefficient of expansion - infrequent need for expansion fittings
— Impact resistant -high tensile strength
— Noncombustible
— Adaptable to future wiring changes
— Low life-cycle costs
— Recyclable

12. Need more information?
Answer: If you have other questions or need additional information regarding steel conduit, its uses, benefits or installation, please contact us at sales@ampleindustriescorp.com.