Junction Box Size Calculator

Device box table 314 16 a shows the minimum permitted box volume to be 18 in 3 and allows up to a maximum of nine 14 awg conductors.

Junction box size calculator.

18 00 cubic inch. Use 314 28 a to size pull boxes junction boxes and conduit bodies when using conductor sizes 4 awg and larger. The width and depth of the pull or junction box depends on the installed raceways. In this case simply multiply your largest raceway size by 8 and that will give you the minimum length for your box.

Do you need to calculate a box size given the wires that are going into the box. The standard method for determining adequate box size first calculates the total box volume and then subtracts the total box fill to ensure compliance. Calculate the minimum pull box width as six times the largest raceway size plus the sum of all other raceways entering the same wall. As an example a 3 inch raceway pull with another 2 inch raceway entering the same wall would be calculated as six times 3 inches plus 2 inches which results in a minimum width of 20 inches.

For a standard 3 in. On the other hand the pull box length must be at least eight times the diameter of the largest conduit. The minimum length required for this box is 16 inches see figure 5. Assume a pull box has four conduit runs and the largest diameter is 4 minimum box length 8 x 4 32 angle pulls u pulls and splices.

Just answer the questions below and we will do the box fill calculations for you based on article 314 16 of the national electrical code. Four switches and receptacles combined x 2 conductors each 8 conductors x 2 25 cu in. A box containing only straight pulls that is calculated by the straight pull method could be too small if there are spliced conductors in the junction box. A junction box with only straight pulls containing spliced 4 awg or larger conductors must comply with the minimum size requirements of 314 28 a 1 and a 2.

An explanation of the sizing requirements of 314 28 a 1 and 2 for larger pull boxes junction boxes and conduit bodies which enclose conductors 4 awg and larger rounds out the information provided here in unit 5. Unless a raceway enters the back of the box no requirement specifies the width or depth. Largest raceway size x 8 minimum box length for example if your raceway is 3. Since the conduits are the same size multiply either by eight.