370-28(a)(2) Angle Pulls

Boxes and conduit bodies used as pull or junction boxes containing conductors of No. 4 or larger, under 600 volts, are calculated from the sizes and numbers of raceways. Section 370-28 provides specific instructions for calculating the dimensions of pull or junction boxes. Two calculation methods are provided—straight pulls and angle or “U” pulls. Last month’s In Focus covered the instructions for sizing pull or junction boxes containing straight pulls. Boxes containing angle or “U” pulls are calculated by a different method.

Where splices, or where angle or “U” pulls are made, the distance between each raceway entry inside the box and the opposite wall of the box must be at least six times the trade diameter of the largest raceway in a row. This distance must be increased for additional entries (in the same row on the same wall of the box) by the amount of the sum of the diameters of all other raceway entries. [370-28(a)(2)]

Calculate the dimensions of a box with angle pulls by starting with one wall where the raceways enter the box, and finding the distance to the opposite end of the box.

The calculations are based upon the same wall where the conduits enter, to the opposite wall of the box, not to where the conductors actually go. First, pick one wall and multiply the largest raceway (trade diameter) by six. If all the raceways are the same size (trade diameter), select any one. Add to that number the trade diameter of all other raceway(s) in the same row, on the same wall of the box. By using a simple formula, this calculation is made easy.

For example, the right side of a box contains two 2-inch conduits, and the top also contains two 2-inch conduits. For the purpose of these illustrations, the left/right (horizontal) dimension is referred to as the “X” dimension, and the top/bottom (vertical) dimension is the “Y” dimension. The minimum length required for the “X” dimension is 14 inches. Since all of the conduits on the right side are 2-inch conduits, multiply two by six (12). Add to that number the other conduit on the same side of the box. (12 + 2 = 14). Since the top of the box contains the same size and number of conduits, the minimum “Y” dimension is also 14 inches.

For boxes containing different-size raceways, simply select the largest size (trade diameter) and multiply by six. Add to that all of the other conduits in the same row on the same side of the box. For example, the right side of a box contains three raceways, one 3-inch and two 2-inch conduits. The top contains one 4-inch, one 3-inch, and one 2-inch conduit. What are the minimum dimensions required for this box?

Since the largest conduit on the right side is 3 inches, multiply three by six (18). Add to that number the other conduits in the same row, on the same side of the box (18 + 2 + 2 = 22). The minimum length required for the “X” dimension is 22 inches. Because the raceways entering the top are not identical to the side of the box, a separate calculation is required. The largest conduit entering the top is 4 inches. Therefore, multiply four by six (24). Add the other conduits in the same row, on the same side of the box, to that number (24 + 3 + 2 = 29). The minimum length required for the “Y” dimension is 29 inches.

Sometimes boxes containing angle pulls have more than one row of raceway entries. Where more than one row of raceways enter a box, calculate each row individually. Use the single row that provides the maximum distance. Each row should be calculated as if it were a separate box.

For example, the front row for the right side of a box contains four 3-inch conduits. The back row for the right side contains three 4-inch conduits. The front row for the top of the box contains one 4-inch, two 3-inch, and one 2-inch conduit. The back row for the top contains five 3-inch conduits. What are the minimum dimensions required for this box? Since there are two rows of conduit entries for both the right side and top of this box, calculate each row separately. The largest conduit for the front row on the right side is 3 inches, multiply three by six (18). Add to that number the other conduits in the same row (18 + 3 + 3 + 3 = 27). The largest conduit for the back row on the right side is 4 inches, multiply four by six (24). Add the other conduits in the same row, on the same side of the box, to that number (24 + 4 + 4 = 32). The minimum length required for the “X” dimension is the larger of the two individually calculated rows, or 32 inches.

The largest conduit entering the top for the front row is 4 inches. Therefore, multiply four by six (24). Add to that number the other conduits in the same row (24 + 3 + 3 + 2 = 32). The largest conduit for the back row on top is 3 inches, multiply three by six (18). Add the other conduits in the same row, on the same side of the box, to that number (18 + 3 + 3 + 3 + 3 = 30). The minimum length required for the “Y” dimension is the larger of the two individually calculated rows, which is 32 inches. (See Figure 5.) Notice that the largest number for the “X” dimension is from the back row, but the largest number for the “Y” dimension is from the front row.

Next month’s In Focus, resuming with Section 370-28(a)(2), will continue discussion of angle and “U” pulls.

MILLER, owner of Lighthouse Educational Services, teaches custom-tailored classes and conducts seminars covering various aspects of the electrical industry. He is the author of Illustrated Guide to the National Electrical Code. For more information, visit his Web site at www.charlesRmiller.com. He can be reached by telephone at (615) 333-3336, or via e-mail at charles@charlesRmiller.com.