Three Inch Electrical Conduit Dimensions

Dimensions of 3" Electrical Conduits Used in North America

Dear Mr. Electrician:  What are Three Inch Electrical Conduit Dimensions?

Answer:  Three Inches (3″) is the trade size, not the actual dimension of the electrical conduit.  Seventy-eight (78) is the metric designator, not the exact dimension in millimeters.

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The dimensions for various types of 3″ electrical conduits are below.  The information was derived from several sources and should not be considered precise.  Dimensions may vary slightly between manufacturers.

A 3 5/8″ (92mm) hole saw is used for 3″ conduit fittings.

Table of Contents:

Read my article about the various types of electrical conduits and their National Electrical Code references.

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METAL ELECTRICAL CONDUIT

3″ Electrical Metallic Tubing (EMT or Thinwall) is a smooth, light-weight, galvanized metal conduit with an inside diameter of 3.356″ or 85.24mm.  The outside diameter is 3.500″ or 88.9mm.  The wall thickness of 3″ EMT is .072″ or 1.83mm.

100 feet of 3″ EMT weighs approximately 263 pounds or 119.3 kilograms.  It requires a 3 5/8″ hole for the conduit fittings.  A tap needs a 3 1/4″ hole.  Threads per inch for the fittings is 8 NPT.

3″ Rigid Metal Conduit (RMC) is a heavy-weight conduit with a galvanized finish throughout.  It has factory threads with a 3/4″ per foot taper, 8 threads per inch NPT.

100′ of 3″ RMC weighs approximately 727 pounds or 329.7 kilograms.  It has an inside diameter of 3.068″ or 77.93mm and an outside diameter of 3.500″ or 88.9mm.  The wall thickness is .205″ or 5.20mm.  3″ Rigid requires a 3 5/8″ hole for the conduit and fittings.  A tap needs a 3 1/4″ hole.

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3″ 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 with a 3/4″ per foot taper, and 8 threads per inch NPT.  It also utilizes the same couplings and fittings as RMC.

100 feet of 3″ IMC weighs approximately 543 pounds or 246.3 kilograms.  3″ IMC has an inside diameter of 3.216″ or 80.7mm.  It has an outside diameter of 3.476″ or 88.3mm.  The wall thickness is .15″ or 3.81mm.

3″ Flexible Metal Conduit (FMC or Greenfield) is a galvanized finished flexible metal electrical conduit composed of a continuously formed interlocking metal strip.

100 feet of 3″ Reduced Wall Steel Greenfield weighs approximately 190 pounds (86.18248 kilograms).  Reduced Wall 3″ Aluminum FMC weighs 77 pounds or 34.926584 kilograms.

3″ FMC has a minimum inside diameter of 3.000″ or 76.2mm.  It has a minimum outside diameter of 3.360″ or 85.344mm and a maximum outside diameter of 3.560″ or 90.424mm.  The minimum bending radius is 18 inches or 457.2mm.  3″ Flex requires a 3 5/8″ hole for the conduit fittings.  A tap needs a 3 1/4″ hole.  Threads per inch for the fittings is 8 NPT.

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3″ Liquidtight 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.  100 feet of 3″ Sealtight weighs 257 pounds or 116.573144 kilograms.

Three-inch Sealtight has an inside minimum diameter of 3.070″ or 77.978mm and a maximum inside diameter of 3.100″ or 78.74mm.  It has a minimum outside diameter of 3.460″ or 87.884mm and a maximum outside diameter of 3.500″ or 88.9mm.  The minimum bending radius is 18 inches (457.2mm).  Fittings require a 3 5/8″ hole.  A tap needs a 3 1/4″ hole.  Threads per inch for the fittings is 8 NPT.

NON-METALLIC ELECTRICAL CONDUIT

3″ Rigid Polyvinyl Chloride Conduit (PVC) schedule 40 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors or underground.  It has some flexibility with an inside diameter of 3.068″ or 77.9272mm.

It has an outside diameter of 3.500″ or 88.9mm.  The wall thickness is .216″ or 5.4864mm.  3″ Schedule 40 weighs 163 pounds per 100 feet (73.935496 kilograms).  3″ PVC requires a 3 5/8″ hole for the conduit fittings.  A tap needs a 3 1/4″ hole.  Threads per inch for the fittings is 8 NPT.

3″ Rigid Polyvinyl Chloride Conduit (PVC) schedule 80 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors or underground.  The inside diameter is 2.9″, and the outside diameter is 3.5″.  The wall thickness is .300″.  It has minimal flexibility.

One hundred feet of 3″ PVC 80 weighs approximately 210 pounds.  3″ PVC requires a 3 5/8″ hole for the conduit fittings.  A tap needs a 3 1/4″ hole.  Threads per inch for the fittings is 8 NPT.




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3″ Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic conduit that is suitable for many conditions.  It has an inside diameter of 3.360″ or 85.344mm.  The outside diameter is 3.500″ or 88.9mm.  The conduit wall thickness is .070″ or 1.778mm.

One hundred feet of three-inch SW RTRC weighs 60 pounds or 27.21552 kilograms.  It requires a 3 5/8″ hole for the conduit fittings.  A tap needs a 3 1/4″ hole.  Threads per inch for the fittings is 8 NPT.

3″ High-Density Polyethylene (HDPE) is a non-metallic flexible conduit available in long reel lengths to reduce joints and installation time.  It has an outside diameter of 3.500″ or 88.9mm.

Three-inch HDPE Type SDR-9 has an inside diameter of 2.675″ or 67.945mm.  100 feet of 3″ HDPE weighs 165 pounds or 74.84268 kilograms.  The wall thickness is .389″ or 9.8806mm.

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All three inch 3″ electrical conduits and fittings require a three-five-eighth (3 5/8″) opening into an electrical box.  The hole can be made with a hole saw or a knockout punch.

A tap for a three-inch (3″) (78) conduit or conduit fittings requires a 3 1/4″ hole.  The threads per inch is 8 National Pipe Thread (NPT).

The standard length for most conduits is ten feet (10′) or 3.048 meters.  Twenty-foot (20′) (6.096 meters) lengths of metal conduit are available but not always in stock.  PVC conduit is available in ten-foot (10′) and some sizes, twenty-foot (20′) lengths.  RTRC mostly comes in twenty-foot (20′) lengths.  The flexible conduits come in coils and reels of various lengths depending on the trade size.  Some electrical supply companies will cut the flexible conduit to length.

See my post describing various electrical conduit types.

Emergency disconnect, service disconnect sticker label as required by the National Electrical Code. CLICK THE IMAGE to see more Emergency Disconnect stickers at my Redbubble Shop.
Emergency Disconnect, Service Disconnect sticker label as required by the National Electrical Code. CLICK THE IMAGE to see more Emergency Disconnect stickers at my Redbubble Shop.

OTHER ELECTRICAL CONDUIT DIMENSIONS

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

1 1/4″ (35)        1 1/2″ (41)         2″ (53)

2 1/2″ (63)        3 1/2″ (91)        4″ (103)

5″ (129)        6″ (155)

For more conduit code details and conduit fill see Chapter 9, Tables 1, 4, 5, and 5A.
See the tables in Informative Annex C at the back of the National Electrical Code (NFPA 70) for the allowable number of wires in each size conduit.

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ELECTRICAL CONDUIT MANUFACTURERS

Aluminum and Steel Conduit Products – https://www.westerntube.com/

Fiberglass Conduit Products – https://championfiberglass.com/

PVC Conduit products – https://www.cantexinc.com/

Steel Conduit Products – https://www.alliedeg.us/

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