How to Determine How Much Pipe to Install in a Junction Box

Determining the amount of electrical pipe, or conduit, to use when installing junction boxes is a straightforward measurement, unless the pipe needs to be bent. Obstacles may be encountered when running the conduit, and making an offset bend increases the length needed to join junction boxes. Electrical junction boxes contain plugs and electrical connections that are part of a conduit wiring system. Electrical conduit protects the wiring used to connect the rest of the system, and precise measurements are required or the pipe will fall short. Oversized conduit can be cut smaller, if necessary. Determining the correct pipe length when bends are involved requires a conduit bending guide.

Electrical conduit
Tape measure
Conduit bending guide
Conduit bender
Pipe cutter
Work gloves
Protective eyewear

Instructions

- 1
  Measure the distance the pipe is to be run, from the junction box to the other end, to determine the basic length of pipe required.
- 2
  Determine the size of the obstruction, if there is one. Using a tape measure, determine the depth of the obstruction. For example, if the pipe needs to be offset over an obstruction that extends 3 inches from the wall, record it as such.
- 3
  Decide on the angle necessary to clear the obstruction. Larger obstructions may require larger angles in order to for the conduit to clear them. Pipe benders are marked with degrees; this should help determine the angle necessary to get around the obstruction.
- 4
  Consult an offset bending guide (several can be found in the Resources) to determine the shrink amount caused by the bend. For example, If an obstruction has a depth of 6 inches and the conduit requires a 30-degree bend, the offset bending guide on the Ideal Industries site (idealindustries.com) identifies the shrink amount as 1-1/2 inches. You should therefore add 1-1/2 inches to the original pipe measurement before cutting to achieve the proper length to get around the obstruction.

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