Six Inch (155) Electrical Conduit Dimensions

Six Inch 6″ is the trade size, not the actual dimension of electrical conduit.  One hundred fifty five 155 is the metric designator not the actual dimension in millimeters.  The dimensions for various types of 6″ electrical conduits are below.  The information was derived from several sources and should not be considered precise.  Dimensions may vary slightly between manufacturers.

6″ Electrical Metallic Tubing (EMT or Thinwall) is a smooth lightweight galvanized metal conduit that doesn’t seem to be available in this size.

6″ (155) 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 6″ RMC weighs approximately 1840 pounds or 834.60928 kilograms.  It has an inside diameter of 6.093″ or 154.76mm.  It has an outside diameter of 6.625″ or 168.28mm.  The wall thickness is .266″ or 6.80mm.  6″ Rigid requires a 6 3/8″ hole for the conduit and fittings.  A tap needs a ??” hole.

6″ Intermediate Metal Conduit (IMC) is a lighter weight version of RMC that does not seem to be available in this size.

6″ Flexible Metal Conduit (FMC or Greenfield) is a galvanized finished flexible metal electrical conduit composed of a continuously formed interlocking metal strip.  It is not available in this size.

6″ (155) 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 6.065″ or 154.05mm.  It has an outside diameter of 6.625″ or 168.28mm.  The wall thickness is .280″ or 7.112mm.  6″ Schedule 40 weighs 409 pounds per 100 feet (185.519128 kilograms).  6″ PVC requires a 6 3/8″ hole for the conduit fittings.  A tap needs a ??” hole.  Threads per inch for the fittings is 8 NPT.

6″ (155) Rigid Polyvinyl Chloride Conduit (PVC) schedule 80 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground.  It has limited flexibility.  Schedule 80 has an inside diameter of 5.761″ or 146.33mm.  It has an outside diameter of 6.625″ or 168.28mm.  The wall thickness is .432″ or 10.9728mm.  6″ Schedule 80 weighs 588 pounds per 100 feet or 266.712096 kilograms.  6″ PVC requires a 6 3/8″ hole for the conduit fittings.  A tap needs a ??” hole.  Threads per inch for the fittings is 8 NPT.

6″ Electrical Nonmetallic Tubing (ENT or Smurf) is a nonmetallic, non-conductive flexible conduit that is not available in this size.

6″ Liguidtight Flexible Metal Conduit (LFMC or Sealtight) is a flexible metal conduit with a non-metallic, non-conductive outer jacket.  It is not available in this size.

6″ Liquidtight Flexible Non-Metallic conduit (LFNC or CarFlex) is a nonmetallic conduit that is suitable for wet conditions.  It is not available in this size.

6″ (155) Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic conduit that is suitable for many conditions.  It has an inside diameter of 6.435″ or 163.449mm.  Outside diameter is 6.627″ or 168.3258mm.  The conduit wall thickness is .096″ or 2.4384mm.  100 feet of six inch MW RTRC weighs 142 pounds or 64.41 kilograms.  It requires a 6 3/8″ hole for the conduit fittings.  A tap needs a ??” hole.  Threads per inch for the fittings is 8 NPT.

6″ (155) 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 6.625″ or 168.275mm.  Type SDR-9 has an inside diameter of 5.065″ or 128.651mm.  100 feet of 6″ HDPE weighs 590 pounds or 267.61928 kilograms.  The wall thickness is .736″ or 18.6944mm.

All six inch 6″ (155) conduit and fittings require a six inch and three eighth 6 3/8″ opening into an electrical box.  The hole can be made with a hole saw or a knockout punch.

A tap for six inch 6″ (155) conduit or conduit fittings requires a ??” 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 in some sizes, twenty foot 20′ lengths.  RTRC mostly comes in twenty foot 20′ lengths.  The flexible conduits come in various length coils and reels depending on the trade size.  Some electrical supply companies will cut flexible conduit to length.

See my post describing various electrical conduit types.

Other size electrical conduits: 1/2″ (16)

3/4″ (21)        1″(27)       1 1/4″ (35)

1 1/2″ (41)        2″ (53)       2 1/2″ (63)

3″ (78)        3 1/2″ (91)       4″ (103)

5″(129)

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