Electrical Conduit pull boxes provide access to successfully pull wires through metallic or non-metallic conduit & raceways.

This article describes the requirements for pull-boxes including sizing & spacing or distances between pull boxes & their locations. We define pull boxes, junction boxes, and terminal boxes and we explain the differences in how these electrical components are used.

This article series describes both metallic electrical conduit and plastic or non-metallic electrical conduit products, and answers basic questions about installing electrical conduit. Electrical conduit is metal or plastic rigid or flexible tubing used to route electrical wires in a building.

The page top photo showing a pull box used to route wires thorugh conduit from a main electrical panel up to a raceway (not shown) that crosses a building to connect in a second, remote electrical panel located in an attached garage.

Electrical Conduit Pull-Box Requirements

A pull box is an electrical box placed at key locations in electrical conduit wiring systems in order to provide access in order to pull electrical wires through conduit during wiring installation.

Illustration: a small pull box or junction box used with EMT or electrical metallic tubing - conduit.

[Click to enlarge any image]

Is a junction box the same as a pull box?

Although the same physical electrical box might be used as either an electrical junction box or a pull-box, their uses are different:

• A pull box is an enclosure through which electrical wires may pass continuously, without electrical splices or connectors. Strictly speaking, a pull box does not contain electrical wire connections.
• A junction box is an enclosure in which there will be one or more breaks in the electrical wire(s), connected by splices or other devices.
  
  In an electrical junction box used to mount or connect a device, wires will be connected to the device such as a light fixture, fan, switch, or electrical receptacle.

Really? While technically a junction box only joins either wires or conduits (raceways), according to some sources that we reviewed, an electrical box might be used as as both a pull box and a splice box.

For example the Crouse-Hinds PTB or PTC pull box enclosures are designed to serve both purposes, allowing the initial pulling of electrical wires during installation and the future access to the wires for changes or additions to the circuits involved.

Pull Box Types

Pull boxes may be described by how the pulled-wires enter and exit the box.

Straight Pull Boxes are those in which the conduit carrying wires is attached to opposite sides of the box to permit a straight-pull of wires through the conduit. These boxes may be installed at intervals along a long straight wire pull to make pulling easier.

Angle Pull Boxes are those in which wires enter the box at a side at right-angles to the side through which they exit the box (angle pulls)

U-Pull Boxes are those in which the wires exit and enter the box through the same side (U-Pulls).

Pull Box Location

The pull box location depends on the number and location of bends in the conduit and in the wire and conduit sizes.

Pull boxes are placed where wires must be pulled through multiple bends in the conduit or raceway routing and where the number of bends exceeds four.

Illustration: a 6-inch PVC junction box produced by Carlon as listed by Home Depot in 2022, for use with Schedule 40 or Schedule 90 conduit. NEMA 6P and type 4/4X ratings and described in detail by citations found at the end of this article.

Pull Box Distances

In a straight run the distance between pull boxes is not limited by the electrical code. It may be limited by physical constraints in the building or even simply by the length of the electrician's fish-tape or pull tape - popular names ofr a pull wire inserted through conduit from a destination end and then used to connect and pull wires to that location from the source-end of the circuit.

In a conduit run that involves bends or changes in direction,

• There shall be no more than the equivalent of four-quarter bends (360 total) between pull points. - NEC 300-13(a)

Pull Box Size

Electrical conduit pull boxes for wires that are No. 4AWG or greater are sized under U.S. NEC article 314.28 given in more-detail below.

• Straight Pull Box size
  
  The pull box minimum length will be the size of the largest raceway or conduit x 8. - source: NEC 314.28(1)(1)
  
  The pull-box minimum depth is determined by the size of the largest conduit & the space required for the locknuts & bushings used to connect to the box
  
  

  Example: a 3-inch conduit will require a pull-box that is (3 x 8) = 24 inches.

  Where more than one conduit is being installed through an individual pull box, the largest conduit connected to the box determines the box size.

• Angle & U-Pull Box Sizes: length between the raceway entry inside the box and the opposing wall of the box must be equal to the sum of
  
  - the trade dimension of the largest conduit x 6
  plus
  - the diameters of all of the other raceway or conduit elements in the row }
  
  source: E-abel, retrieved 2022/05/23 original source: https://www.eabel.com/pull-box-vs-junction-box/
  
• Combined Straight & Angle Pull Box Size: use both straight-pull & angle pull calculations and choose the result that gives the largest box size.

The "conduit size" or diameter is interpreted to be the "trade size" or "metric designator" of the conduit, which may be slightly different than its actual physical dimension or diameter.

Watch Out:  Do not attempt to work on your electrical wiring, switches, or outlets unless you are properly trained and equipped to do so. Electrical components in a building can easily cause an electrical shock, burn, or even death.

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: what's the distance between pull boxes for straight conduit and where there are conduit bends?

What the Distance of Pull boxes in Straight conduiting and at how many bend Junction box Pull box recommended as per NEC NAFA. - Ak Kahn, 2022/05/23

This Q&A were posted originally at ELECTRICAL CONDUIT, METALLIC

Moderator reply: permitted distance between pull boxes for electrical conduit

Thank you for a helpful question.

Bottom line:

The distance between electrical conduit pull boxes in a straight run is not limited by the electrical code.

The distance between electrical conduit pull boxes where there are bends depends on the location of the bends and *their* distances apart, since the NEC 300-13(a) says

“There shall be no more than the equivalent of four-quarter bends (360 total) between pull points.”

Details:

The distance between pull boxes will depend on the number of bends in the conduit between pull boxes (details below), conduit size and tpe, number of conductors & their size.

Key really is the number of bends; straight pulls are easy even over great length.

US NEC 300-13(a) - the maximum distance between pull boxes depends on the length of the conductors.

There shall be no more than the equivalent of four-quarter bends (360 total) between pull points.

The distance between electrical conduit raceway entries enclosing the same conductors must be at least six times the trade size (metric designator) of the larger raceway.

Elecctrical pull boxes for straight-pulls through conduit

2-inch raceways carrying the same conductors would have to be no less than (2 x 6 = 12) 12” apart.
3-inch raceways carrying the same conductors would have to be no less than (3 x 6 = 18) 18” apart.

Notice that these are minimum, not maximum distances. Long straight runs are not so difficult as would be runs incorporating bends.

Electrical conduit pull boxes where there are bends

It’s the US NEC reqiuerment that “there shall be no more than the equivalent of four quarter-bends (360 deg total) between pull points that governs the location and thus distance between those pull boxes.

Useful NEC sections for conduit pull boxes:

US NEC 300.14 - Boxes, conduit bodies, fittings & manholes, installation and use,
includes a descriptin of free conductors allowed within a conduit or box or device including pull boxes and junction boxes

US NEC 314 Electrical boxes, fill, sizing, etc.

US NEC 314 Part V describes Pull & Junction Boxes for systems greater than 600VAC

US NEC 34.15 Damp, Wet or Hazardous Locations

US NEC 314.16 Number of Conductors in Outlet, Device and Junction Boxes, and Conduit Bodies (18 - 6 AWG)

314.16(A) Box Volume Calculations

314.16(B) Box Fill Calculations

(The volume of the box calculated in part A must be equal or greater than the fill calculation given by part B)

US NEC 314.28 Pull and Junction Boxes and Conduit Bodies. Angle Pulls, U Pulls & Splices.

discusses the requirements for the size, dimensions, location and use of pull boxes. Specifically, see all of the requirements given in sections 314.28(A)(1)-(3). You’ll see requirements for dimensions of the boxes

— Electrical Code Excerpt for Electrical Conduit (Raceway) Pull Box Requirements -

(1) Straight Pulls

In straight pulls, the length of the box or conduit body shall not be less than eight times the metric designator (trade size) of the largest raceway.

(2) Angle or U Pulls, or Splices

Where splices or where angle or U pulls are made, the distance between each raceway entry inside the box or conduit body and the opposite wall of the box or conduit body shall not be less than six times the metric designator (trade size) of the largest raceway in a row.

This distance shall be increased for additional entries by the amount of the sum of the diameters of all other raceway entries in the same row on the same wall of the box. Each row shall be calculated individually, and the single row that provides the maximum distance shall be used.

Exception: Where a raceway or cable entry is in the wall of a box or conduit body opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A).

The distance between raceway entries enclosing the same conductor shall not be less than six times the metric designator (trade size) of the larger raceway.

When transposing cable size into raceway size in 314.28(A)(1) and (A)(2), the minimum metric designator (trade size) raceway required for the number and size of conductors in the cable shall be used.

(3) Smaller Dimensions

Listed boxes or listed conduit bodies of dimensions less than those required in 314.28(A)(1) and (A)(2) shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used) permitted by Table 1 of Chapter 9.

Listed conduit bodies of dimensions less than those required in 314.28(A)(2), and having a radius of the curve to the centerline not less than that indicated in Table 2 of Chapter 9 for one-shot and full-shoe benders, shall be permitted for installations of combinations of conductors permitted by Table 1 of Chapter 9. These conduit bodies shall be marked to show they have been specifically evaluated in accordance with this provision.

Where the permitted combinations of conductors for which the box or conduit body has been listed are less than the maximum conduit or tubing fill permitted by Table 1 of Chapter 9, the box or conduit body shall be permanently marked with the maximum number and maximum size of conductors permitted.

For other conductor sizes and combinations, the total cross-sectional area of the fill shall not exceed the crosssectional area of the conductors specified in the marking, based on the type of conductor identified as part of the product listing.

Research & Code Citations for Electrical Conduit Pull Boxes

• Chapman Electric Supply, HOW TO CALCULATE UNDERGROUND PULL BOX SIZE [PDF] - retrieved 2022/05/23 original source: https://shop.chapmanelectric.com/resources/pull-box-sizing
• Colorado, STANDARD PULL BOX DESIGN [PDF] Colorado Department of Transporation, retrived 2022/05/23 original source: https://www.codot.gov/
• E-abel, Pull Box vs Junction Box [PDF] E-Abel R&D, Singapore 22 Pioneer Crescent #02-06 West Park BizCentral Singapore 628556 Email: enclosure@eabel.com +86 13825180452 +86 15050640976 +86 13825180430 - retrieved 2022/05/23, original source: https://www.eabel.com/pull-box-vs-junction-box/
• Tennessee DOT., CHAPTER 10 TRAFFIC SIGNAL DESIGN – PULL BOXES, CONDUITS, AND WIRING [PDF] Tennessee State Government, Web: https://www.tn.gov/directory/department-directory.html, retrieved 2022/05/23, original source:
  Excerpt:
  
  A pull box is an underground compartment made of various materials, such as pre-cast concrete or polymer concrete (composite). When possible, pull boxes should be located adjacent to the sidewalk rather than in the sidewalk. Pull boxes used in traffic signal installations shall meet current TDOT standards and specifications (See TDOT Standard Drawing T-SG-2).
  
  The purpose of pull boxes is:
  
  - To provide access to underground detectors and interconnect cables;
  
  - To provide locations to consolidate separate runs of signal and detector cables;
  
  - To provide locations to facilitate the pulling of long runs of detector or interconnect cables;
  
  - To provide locations to store spare lengths of signal detector or interconnect cables.
• Thomas & Betts Co. / Carlon RIGID NON-METALLIC CONDUIT FITTINGS [PDF]
• Thomas & Betts Co. / Carlon PRODUCT GUIDE SECTION 26 05 33.21 NON-METALLIC JUNCTION BOXES [PDF]
• U.S. NEC, National Electrical Code Section 314.28 Pull and Junction Boxes and Conduit Bodies, National Electrical Code 2020 of Minnesota > 3 Wiring Methods and Materials > 314 Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; And Handhole Enclosures > 314.28 Pull and Junction Boxes and Conduit Bodies - retrieved 2022/5/23 original source: https://up.codes/s/pull-and-junction-boxes-and-conduit-bodies
  

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