One Inch Electrical Conduit Dimensions

Dimensions of Various Types of One Inch Electrical Conduit

Dear Mr. Electrician:  What are one-inch electrical conduit dimensions?

Answer: One-inch electrical conduit dimensions differ from the trade size.  1″ is the trade size, and twenty-seven (27) is the metric designator, not the actual dimension in millimeters.

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Use a 1-3/8″ (35mm) hole saw for one-inch conduit fittings.

Hole saw sizes for all electrical conduits can be found on this post.

The dimensions for various types of 1″ electrical conduits are below.  The information was derived from several sources and should not be considered precise.  Dimensions may vary slightly between manufacturers.

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METAL ELECTRICAL CONDUIT


1″ Electrical Metallic Tubing (EMT or Thinwall) is a smooth, lightweight galvanized metal conduit with an inside diameter of 1.049″ or 26.64mm.  The outside diameter is 1.163″ or 29.54mm.  The wall thickness of 1″ EMT is 0.057″ or 1.45mm.

100 feet of 1″ EMT weighs approximately 67 pounds or 30.4 kilograms. The conduit fittings require a 1-3/8″ hole.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5, NPT.

1″ 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, 11.5 threads per inch NPT.  100′ of one-inch RMC weighs approximately 161 pounds or 73 kilograms.

One-inch RMC has an inside diameter of 1.049″ or 26.64mm.  It has an outside diameter of 1.315″ or 33.4mm.  The wall thickness is 0.126″ or 3.20mm.  1″ Rigid requires a 1-3/8″ hole for the conduit and fittings.  A tap needs a 1-5/32″ hole.

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1″ 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 11.5 threads per inch NPT.  It also utilizes the same couplings and fittings as RMC.

100 feet of 1″ IMC weighs approximately 119 pounds or 54 kilograms.  1″ IMC has an inside diameter of 1.120″ or 28.1mm.  It has an outside diameter of 1.29″ or 32.8mm.  The wall thickness is 0.093″ or 2.35mm.

  CLICK HERE to See Conduit Bodies Available on Amazon

1″ 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 1″ Reduced Wall Steel Greenfield weighs approximately 57 pounds (25.854744 kilograms).  Reduced Wall one-inch Aluminum FMC weighs 20 pounds or 9.07 kilograms.

1″ FMC has a minimum inside diameter of 1.000″ or 25.4mm and a maximum inside diameter of 1.040″ or 26.416mm.  It has a minimum outside diameter of 1.300″ or 33.02mm and a maximum outside diameter of 1.380″ or 35.052mm.  The minimum bending radius is 6 inches or 152.4mm.  1″ Flex requires a 1-3/8″ hole for the conduit fittings.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5, NPT.

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1″ 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 1″ Sealtight weighs 78 pounds or 35.38 kilograms.

One inch Sealtight has an inside minimum diameter of 1.041″ or 26.44mm and a maximum inside diameter of 1.066″ or 27.08mm.  It has a minimum outside diameter of 1.290″ or 32.766mm and a maximum outside diameter of 1.315″ or 33.40mm.  The minimum bending radius is 6 inches (152.4mm).  Fittings require a 1-3/8″ hole.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5 NPT.

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NON-METALLIC ELECTRICAL CONDUIT

1″ Rigid Polyvinyl Chloride Conduit (PVC) schedule 40 is a nonmetallic, non-conductive electrical conduit that is good to use indoors, outdoors, or underground.  It has some flexibility with an inside diameter of 1.049″ or 26.64mm.  It has an outside diameter of 1.315″ or 33.40mm.  The wall thickness is .133″ or 3.38mm.

1″ Schedule 40 weighs 34 pounds per 100 feet (15.42 kilograms).  One inch PVC requires a 1-3/8″ hole for the conduit fittings.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5 NPT.

1″ Rigid Polyvinyl Chloride Conduit (PVC) schedule 80 is a nonmetallic, non-conductive electrical conduit that is good to use indoors, outdoors, or underground.  It has limited flexibility.

Schedule 80 has an inside diameter of .957″ or 24.31mm. It has an outside diameter of 1.315″ or 33.40mm.  The wall thickness is .179″ or 4.55mm. 1″ Schedule 80 weighs 44 pounds per 100 feet or 19.958048 kilograms.  One-inch PVC requires a 1-3/8″ hole for the conduit fittings.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5 NPT.

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1″ Electrical Nonmetallic Tubing (ENT or Smurf) is a nonmetallic, non-conductive flexible conduit with an inside diameter of 1″ or 25.4mm.  It weighs 20 pounds per 100 feet or 9.07184 kilograms.

1″ ENT has an outside diameter of 1.315″ or 33.40mm.  The minimum bend radius is 6 inches.  One-inch fittings require a 1-3/8″ hole.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5.

1″ Liquidtight Flexible Nonmetallic Conduit (LFNC or CarFlex) is a nonmetallic conduit suitable for wet conditions.  100′ of 1″ Carflex weighs 28 pounds.  It has an inside minimum diameter of 1.041″ or 26.44mm and a maximum inside diameter of 1.066″ or 27.07mm.

One-inch LFNC has a minimum outside diameter of 1.290″ or 32.76mm and a maximum outside diameter of 1.315″ or 33.40mm.  The minimum bending radius is 6 inches or 146mm.  The conduit fittings require a 1-3/8″ hole.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5 NPT.

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1″ Reinforced Thermosetting Resin Conduit (RTRC or Fiberglass) is a nonmetallic conduit suitable for many conditions.  It has an inside diameter of 1.175″ or 29.84mm.  The outside diameter is 1.315″ or 33.40mm.  The conduit wall thickness is .070″ or 1.778mm.

One hundred feet of one-inch RTRC weighs 19 pounds or 8.618248 kilograms.  The conduit fittings require a 1-3/8″ hole.  A tap needs a 1-5/32″ hole.  Threads per inch for the fittings is 11.5 NPT.

1″ 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 1.315″ or 33.40mm.

Type SDR-9 has an inside diameter of 1.003″ or 25.4762mm.  100 feet of 1″ HDPE weighs 24 pounds.  The wall thickness is 0.146″ or 3.7084mm.

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ONE-INCH CONDUIT TAP AND DIE SIZES

All one-inch (1″) conduit and fittings require an inch and three eighth 1-3/8″ (35mm) opening into an electrical box.  The hole can be made with a hole saw or a knockout punch.

One-inch electrical conduit uses a standard 1″ NPT (National Pipe Taper) tap and dies for threading.  A 1″ conduit tap requires a 1-5/32″ hole.  The threads per inch are 11.5. The taper is 3/4″ per foot.

However, there are NPS (National Pipe Straight) threads in some cases, such as on some fittings.  NPS threads require a 1-3/16″ hole for a one-inch NPS conduit tap.

My rule of thumb for determining if a conduit or electrical fitting is NPS or NPT is to notice if the fitting came with a locknut. If it came with a locknut, it is not meant for threading into a pipe and is an NPS thread. If you tried to screw one of these into an NPT fitting, such as a threaded condulet, it would not thread all of the ways due to the condulet having a tapered 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 coils and reels of various lengths, depending on the trade size.  Some electrical supply companies will cut the flexible conduits to length.

See my post describing various electrical conduit types.

Emergency disconnect, service disconnect sticker label as required by article 230.85 in the National Electrical Code. CLICK THE IMAGE to see more Emergency Disconnect Stickers.
Emergency Disconnect, Service Disconnect sticker label as required by article 230.85 in the National Electrical Code. CLICK THE IMAGE to see more Emergency Disconnect Stickers.

OTHER SIZE ELECTRICAL CONDUITS

1/2″ (16)       3/4″ (21)       1 1/4″ (35)

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

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

5″ (129)       6″ (155)

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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.

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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