Dear Mr. Electrician: What are the dimensions of six inch electrical conduit?
Answer: 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. NOTE: Some text links go to applicable products on Amazon and EBay.
The actual dimensions for various types of 6″ electrical conduit are below. The information was derived from several sources and should not be considered precise. Dimensions may vary slightly between manufacturers.
Use a 6 5/8″ (168mm) hole saw for six inch conduit fittings.
Click here for my post with more detailed descriptions of various types of electrical conduit and their code references, without dimensions.
SIX INCH ELECTRICAL CONDUIT DIMENSIONS
6″ 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.
Six inch RMC 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 5/8″ hole for the conduit and fittings.
6″ Rigid Polyvinyl Chloride Conduit (PVC) schedule 40 is a nonmetallic, non-conductive electrical conduit that is approved for use indoors and outdoors, or underground.
Six inch PVC 40 has an inside diameter of 6.065″ or 154.05mm. It has some flexibility and 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 5/8″ hole for the conduit fittings. Threads per inch for the fittings is 8 NPT.
6″ Rigid Polyvinyl Chloride Conduit (PVC) schedule 80 is a nonmetallic, non-conductive electrical conduit that is good to use indoors and outdoors, or underground.
Six inch PVC 80 has limited flexibility with 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 5/8″ hole for the conduit fittings. Threads per inch for the fittings is 8 NPT.
6″ Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic conduit that is suitable for many conditions.
Six inch RTRC Fiberglass Conduit 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 5/8″ hole for the conduit fittings. Threads per inch for the fittings is 8 NPT.
6″ High Density Polyethylene (HDPE) is a non-metallic flexible conduit available in long reel lengths to reduce joints and installation time.
Six inch HDPE 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 five eighths 6 5/8″ opening into an electrical box. The hole can be made with a hole saw.
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.
See my post describing various electrical conduit types.
OTHER ELECTRICAL CONDUIT DIMENSIONS
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.