Sizing Pull Boxes — Art. 370
Choose the best answer. (Assume all conductors pulled through the conduits in Questions 1-5 are No. 4 and larger.)
1. What is the minimum length pull box required for a straight pull having a run of 2-in. conduit entering and leaving opposite walls of the box?
(a) 12 in.
(c) 16 in.
(b) 14 in.
(d) 18 in.
2. What is the minimum size pull box required for a straight pull having parallel runs of 2½-in., 2-in., and 1½-in. conduit entering and leaving opposite walls of the box?
(a) 14 in.
(c) 18 in.
(b) 16 in.
(d) 20 in.
3. What is the minimum size pull box required for an angle pull with a run of 2-in. conduit that enters the top left wall and leaves the bottom right wall of the box?
(a) 8 in. x 8 in.
(b) 12 in. x 12 in.
(c) 14 in. x 14 in.
(d) 16 in. x 16 in.
4. What is the minimum size pull box required for an angle pull with runs of 4-in., 3-in., and 2-in. conduit entering and leaving the box?
(a) 29 in. x 29 in.
(b) 30 in. x 30 in.
(c) 32 in. x 32 in.
(d) 36 in. x 36 in.
5. What is the minimum size pull box required for a U-pull having a run of 2-in. conduit?
(a) 10 in. x 10 in.
(b) 12 in. x 12 in.
(c) 14 in. x 14 in.
(d) 16 in. x 16 in.
Answers and Discussion
1. (c). When sizing a pull box for a straight pull (conduits on opposite walls), multiply the dimension of the largest size conduit entering and leaving the box by a specified multiplier.
Step 1: Find the appropriate multiplier in Sec. 370-28(a)(1).
Multiplier = 8
Step 2: Calculate the required length.
2 in. x 8 = 16 in.
Solution: The minimum length of the pull box is 16 in.
Stallcup’s Code Loop: Sec. 370-28(a) and 370-28(a)(1).
2. (d). Junction boxes with more than two conduits connected to their sides (to form a straight pull) are sized by multiplying the trade diameter of the largest raceway by a specified multiplier. The dimensions of the remaining conduits do not factor into this calculation.
Step 1: Find the appropriate multiplier in Sec. 370-28(a)(1).
Multiplier = 8
Step 2: Calculate the required length.
2½ in. x 8 = 20 in.
Solution: The minimum length of the pull box is 20 in.
Stallcup’s Code Loop: Sec. 370-28(a) and 370-28(a)(1).
3. (b). When sizing a pull box for an angle pull, multiply the trade diameter of the largest conduit entering and leaving by a specified multiplier.
Step 1: Find the appropriate multiplier in Sec. 370-28(a)(2).
Multiplier = 6
Step 2: Calculate the required length.
2 in. x 6 = 12 in.
Solution: The minimum dimension of the pull box is 12 in. x 12 in.
Stallcup’s Code Loop: Sec. 370-28 and 370-28(a)(2).
4. (a). Junction boxes with more than one run of conduit connected to their walls to form an angle pull are sized by multiplying the trade diameter of the largest conduit by a specified multiplier and adding the dimensions of the remaining conduits to this value.
Step 1: Find the appropriate multiplier in Sec. 370-28(a)(2).
Multiplier = 6
Step 2: Calculate the required length.
4 in. x 6 = 24 in.
Step 3: Now add the diameters of the remaining conduits.
24 in. + 3 in. + 2 in. = 29 in.
Solution: The minimum dimension of the pull box is 29 in. x 29 in.
Stallcup’s Code Loop: Sec. 370-28 and 370-28(a)(2)
5. (b). Junction boxes with more than one run of conduit connected to their walls to form a U-pull are sized by multiplying the trade diameter of the largest conduit by a specified multiplier and adding the dimensions of the remaining conduits to this value.
Step 1: Find the appropriate multiplier in Sec. 370-28(a)(2).
Multiplier = 6
Step 2: Calculate the required length.
2 in. x 6 = 12 in.
Solution: The minimum dimension of the pull box is 12 in. x 12 in.
Stallcup’s Code Loop: Sec. 370-28(a) and 370-28(a)(2).
