Electrical Conduit Types 2019

Examples of PVC Schedule 40 Electrical Conduit. The labeling on the conduit is also depicted.
Examples of PVC Schedule 40 Electrical Conduit. Note the labeling on the edge of the conduit. All types of electrical conduit are labeled.

Dear Mr. Electrician: I am making plans to build a new house for myself.  I have an architect working on drawings and I want to add some specifications to them.  I do not plan on doing all of the work myself, but I want to be sure that all of my installation requirements are met.  To that end I would like to know the differences between various electrical conduit types to determine what might be best for my particular construction project?

Answer: Below is a list with brief descriptions of the common electrical conduit types installed in North America.  The uses are not fully mentioned nor are the code requirements.  Some of that is copyrighted material and would be too long to post here.  Your best bet is to get a copy of the National Electrical Code (NFPA 70) and read the relevant section for each particular electrical conduit type and also for other electrical requirements pertaining to your project.  The electrical code article numbers are listed in the electrical conduit descriptions below.  NOTE: Text links below go to applicable products on Amazon.

Links to conduit dimensions are listed at the bottom.

Types of Electrical Conduit Used in North America

Electrical Metallic Tubing (EMT or Thinwall) is a smooth lightweight galvanized metal conduit that can be used in dry or damp locations.  It is easy to work with and needs appropriate couplings and connectors when joined together or entering a junction box.   EMT can be bent by using the proper bending tool for each of the designated trade sizes.  The standard length for EMT is ten feet 10′ or 3.048 meters.  Pre-bent elbows and twenty foot 20′ (6.096 meters) lengths are available for some sizes.  Tables C.1 and C.1(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in EMT conduit.   Article 358 tells you the installation requirements.  EMT is manufactured in several colors to distinguish different electrical systems such as fire alarm circuits from power circuits.  EMT is mostly available in sizes 1/2″ to 4″ (16mm to 103mm).

Rigid Metal Conduit (RMC or Rigid) is a heavy weight metal electrical conduit type with a galvanized finish throughout that can be used indoors, outdoors, and in the ground.  It is factory threaded at each end and is usually furnished with one coupling attached.  Threaded and also compression couplings and connectors are available.  For hazardous locations, explosion proof fittings are available.  The standard length for Rigid is ten feet 10′ or 3.048 meters.  Pre-bent elbows and twenty foot 20′ (6.096 meters) lengths are available for some sizes.  RMC can be bent using the correct bending tool for each of the designated sizes.  Tables C.9 and C.9(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in RMC conduit.  See Article 344 for code installation requirements.  Rigid is available in 1/2″ to 6″ sizes or 16mm to 155mm.

Intermediate Metal Conduit (IMC) is a lighter weight version of RMC.  It has a galvanized finish inside and out and can be used in many of the same environments as RMC.  It has factory threads at each end and is usually furnished with one coupling attached.  It also utilizes the same threaded and compression couplings and connectors as RMC.  IMC can be bent using the proper bending tool for each of the designated sizes.  The standard length for IMC is ten feet 10′ or 3.048 meters.  Pre-bent elbows and twenty foot 20′ (6.096 meters) lengths are available for some sizes.  Tables C.4 and C.4(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in IMC conduit.  Article 342 explains the requirements for installation.  IMC is available in sizes 1/2″ to 4″ or 16mm to 103mm.

Flexible Metal Conduit (FMC or Greenfield) is a galvanized finished flexible metal electrical conduit type composed of a continuously formed interlocking metal strip.  It is for dry indoor installations.  It is easy to work with and needs appropriate couplings when joining and connectors when entering a junction box.  Bushings are usually required inside the conduit ends.  FMC is available in steel and aluminum.  Dimensions may vary slightly between the two metal types.  The same HW (Heavy wall) straps used for RMC and IMC can also support FMC.  The minimum bending radius is 5 inches or 101.6mm, but increases for each size.  Standard coil length is 100 feet or 30.48 meters.  Also available on reels.  Some electrical supply companies will cut it to length as needed.  Tables C.3 and C.3(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in FMC conduit.  Article 348 explains the installation guidelines.  Flexible Metal Conduit is available from size 3/8″ to size 4″ (12mm to 103mm).

Rigid Polyvinyl Chloride Conduit (PVC) schedule 40 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground.  PVC conduit is sold with one coupling on the end.  It has some flexibility, but it can also be heated and bent.  Pre-bent elbows are available for some sizes.  Although there are PVC straps available, the same HW (Heavy wall) straps used for RMC and IMC can also support PVC.  PVC conduit is joined using special glue along with the appropriate couplings and adaptors.  PVC glue has solvent in it to soften the plastic so that the joint is welded together.  When joining PVC the glue must be applied to the conduit end as well as to the fitting.  Do not use old cans of PVC glue as most of the solvent will have evaporated causing the glue to be less effective.  PVC is available in 10 foot (3.048 meters) and 20 foot (6.096 meters) lengths.  Tables C.11 and C.11(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in PVC schedule 40 conduit.  Read about its expansion characteristics and how to compensate for them in Article 352.  Schedule 40 is available in sizes 1/2″ to 6″ or 16mm to 155mm.

Rigid Polyvinyl Chloride Conduit (PVC) schedule 80 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground.  Schedule 80 PVC has a thicker wall than Schedule 40.  PVC conduit is sold with a coupling molded onto one end.  It has limited flexibility, but can be heated and bent to any angle.  Pre-bent elbows are available for some sizes.  There are PVC straps available, however the same HW (Heavy wall) straps used for RMC and IMC can also support PVC.  PVC conduit is joined using appropriate fittings with special glue.  PVC glue has solvent in it to soften the plastic so that the joint is welded together.  When joining PVC the glue must be applied to the conduit end as well as to the fitting.  Do not use old cans of PVC glue as most of the solvent will have evaporated, rendering the glue less effective.  PVC schedule 80 is available in 10 foot (3.048 meters) and 20 foot (6.096 meters) lengths.  Tables C.10 and C.10(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in PVC schedule 80 conduit.  PVC expansion characteristics and how to compensate for them are in Article 352.  Schedule 80 is available in sizes 1/2″ to 6″ or 16mm to 155mm.

Electrical Nonmetallic Tubing (ENT or Smurf) is a nonmetallic, non-conductive flexible conduit.  The minimum bend radius is 6 inches.  Available in 10 foot (3.048 meters) lengths, or coils and reels.  There are couplings, fittings, and electrical boxes made specifically for ENT.  Tables C.2 and C.2(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted inside of ENT conduit.  Article 362 describes how it can be used.  ENT is available in colors, yellow for communication circuits, red for fire alarms, and blue for power.  It is important to use the correct transition adapters when terminating ENT into an electrical box.  ENT is available in sizes 1/2″ to 2″ (16mm – 53mm).

Liguidtight Flexible Metal Conduit (LFMC or Sealtight) is a flexible metal conduit with a non-metallic, non-conductive outer jacket that makes it suitable for use in wet locations.   The minimum bending radius is 5 inches, but increases for each size.  LFMC is terminated using metal connectors designed and approved specifically for use with it.  It is available in 100 foot coils or on reels.  Many electrical supply companies will cut it to length.  Tables C.8 and C.8(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in LFMC conduit.  Read about it’s approved uses in Article 350.  Sealtight is available in sizes 3/8″ to 4″ or 12mm to 103mm.

Liguidtight Flexible Nonmetallic Conduit (LFNC or Carflex) is a nonmetallic conduit that is suitable for wet conditions.  The minimum bending radius is 5 inches, but increases for each size.  LFNC is terminated using non-metallic connectors designed and approved specifically for its use.  It is available in 100 foot coils or on reels.  Many electrical supply companies will cut it to length.  Tables C.5, C.6, C.7 and C.5(A) C.6(A), and C.7(A) in the National Electrical Code (NFPA 70) tell you how many conductors are permitted in LFNC conduit.  See article 356.2(1), (2), and (3) to understand the different types of LFNC.  Carflex is available in 3/8″ to 2″ sizes (12mm – 53mm)

Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic electrical conduit type that is suitable for many conditions.  Larger sizes are available in 20 foot lengths only.  Pre-bent factory elbows are available.  RTRC conduit can also be bent using heat along with a hydraulic conduit bender.  RTRC must be installed with fittings approved for use with this type of conduit.  Conduit and fittings are joined using a two part epoxy glue.  Conduit ends and the inside of fittings must be sanded using emery cloth.  Expansion couplings are required on installations over 50 feet long.  Article 355 in the National Electrical Code (NFPA 70) details the uses for RTRC conduit.  See Chapter 9, Table 1 to determine the number of conductors permitted.  Fiberglass is available in 3/4″ to 6″ sizes and 21mm to 155mm.

High Density Polyethylene (HDPE) is a non-metallic flexible conduit available in long reel lengths to reduce joints and installation time.  It is not used for exposed applications.  This conduit is commonly used by utility companies for underground use.  See article 353 in the National Electrical Code (NFPA 70) for its permitted uses.  Read Chapter 9, Table 1 to determine the number of conductors allowed.  HDPE is available in sizes 1/2″ to 12″.

Other types of conduit available, but not described here are: PVC Coated Metal Conduit, Aluminum Rigid, Stainless Steel, Innerduct, Wiremold.

Most of the available fittings for the various size and types of conduits, and even the conduits themselves will not always be readily available.  Distributors don’t like to keep things on their shelves too long, consequently they tend to stock items that sell quickly.  Some of the bigger electrical supply companies will have large central warehouse hubs where stock is stored and delivered to their satellite locations.

10′ (Ten feet) of conduit = 120″ (Inches), 3.333333333 Yards, 3048 Millimeters, 304.8 Centimeters, 30.48 Decimeters, and 3.048 Meters.

See my post on hole saw and knockout punch sizes to determine the hole needed for each size conduit.

Conduit Dimensions

1/2″ (16)       3/4″ (21)      1″ (27)

1.25″ (35)       1.5″ (41)      2″ (53) 

2.5″ (63)       3″ (78)       3.5 (91)

4″(103)       5″ (129)       6″ (155)

My old html page for conduit dimensions can be found here.  It did not copy over to WordPress well.