Calculator
Formula Used
Straight pull: Minimum box length = 8 × largest raceway trade size.
Angle pull, U-pull, or splice: Minimum distance to opposite wall = 6 × largest raceway in the same row + sum of other raceways in that row.
U-pull spacing: Minimum raceway spacing = 6 × largest raceway enclosing the same conductors.
The calculator checks width and height separately. It then adds any allowance and rounds up.
Example Data Table
| Case | Pull Type | Input | Minimum Result |
|---|---|---|---|
| 1 | Straight | Largest raceway 4 in | 32 in |
| 2 | Angle | 4, 2 in row | 26 in |
| 3 | U-Pull | 3 in paired raceway | 18 in spacing |
| 4 | Splice | 3, 2, 2 in row | 22 in |
How to Use This Calculator
Select the pull type first. Use straight pull when conductors pass through opposite walls. Use angle pull when conductors turn inside the box. Use U-pull when conductors enter and leave the same wall. Use splice when conductors are joined inside the box.
For straight pulls, enter the largest raceway on the horizontal axis. Also enter the largest raceway on the vertical axis when needed. For angle, U-pull, or splice layouts, enter raceway trade sizes for each wall row. Separate values with commas.
Enter actual box dimensions if you want a pass or review check. Use the allowance field when your shop standard needs extra room. Press calculate to show results above the form.
Advanced Pull Box Sizing Guide
Why Pull Box Size Matters
Pull box sizing protects conductors during installation. Large conductors need bending room. Tight boxes increase pulling force. They also raise the risk of damaged insulation. A careful size check helps avoid rework.
Know the Pull Type
The pull type controls the formula. A straight pull is direct. Conductors enter one side and leave the opposite side. This layout uses the eight-times rule. An angle pull changes direction inside the box. A splice box also needs more working distance. U-pulls add spacing concerns because conductors return to the same wall.
Rows and Walls
Rows matter in angle calculations. Do not mix every raceway on one wall into one total unless they share the same row. Check each row. The largest row result controls that wall. Then compare opposite wall distances. The box must satisfy the controlling width and height.
Using Allowance
The minimum value is not always the best field value. Extra room can help cable pulling. It can also help future additions. This calculator lets you add an allowance. It also rounds results to a selected increment. That makes ordering easier.
Field Review
Always measure inside dimensions. Outside dimensions can be misleading. Covers, hubs, bushings, liners, and fittings may reduce clear space. Check raceway spacing before final layout. U-pulls and angle pulls need correct entry separation. Review local requirements before installation.
Practical Use
Designers can use this tool during layout. Estimators can compare box sizes. Installers can confirm field changes. Inspectors can review submitted dimensions. The result is a fast planning aid. It does not replace final code review. Use it with current project documents and approved trade sizes.
FAQs
1. What is a pull box?
A pull box is an enclosure used to pull, route, splice, or redirect conductors. It gives installers space to handle conductors safely.
2. Which rule applies to straight pulls?
Straight pulls use eight times the largest raceway trade size on the pull axis being checked.
3. Which rule applies to angle pulls?
Angle pulls use six times the largest raceway in a row, plus the sum of the other raceways in that same row.
4. Are splices treated like straight pulls?
No. Splice boxes are commonly checked using the angle-pull method. The box needs room for conductor bending and joining.
5. What is a U-pull?
A U-pull happens when conductors enter and leave the same wall. It needs wall distance checks and same-conductor raceway spacing checks.
6. Should I enter inside or outside box dimensions?
Use inside dimensions. The required distance is based on usable internal space, not the outside shell measurement.
7. Why does the calculator ask for rows?
Angle and U-pull calculations apply to raceways in the same row on the same wall. Separate rows should be checked separately.
8. Can this replace professional review?
No. It is a planning tool. Always confirm final sizing with current code, project specifications, and the authority having jurisdiction.