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How to Estimate HDPE Conduit Runs for Underground Installation

HDPE conduit is the ideal choice for installing electrical and communication cables in underground applications. It is flexible, durable and lightweight, making it easy to work with. Accurately estimating conduit runs is essential for a successful and on-budget installation.

Step 1: Preliminary Questions

Before you begin estimating conduit runs, it's crucial to gain an understanding of the project as a whole. You will want to answer all the following questions:

  1. Conduit Type and Size: What type and size of HDPE conduit will be used?
  2. Cable Types and Quantities: What types of cables will run through the conduit? What are size(s) of each of the cables?
  3. Route and Layout: Are there any bends, turns, or obstacles along the install route that may affect the installation?
  4. Regulations and Codes: What are the local electrical codes and regulations? Are there any specific requirements for conduit spacing, depth, and support?

Step 2: Calculate Conduit Capacity

The NEC (National Electric Commission) sets standards for the percent of conduit that can be filled with cables. You can use our handy Conduit Wire Fill Charts & Tables to help determine how many cables can be installed within your conduit, or determine what size of conduit is needed for your cables. Either way, you will want to make sure you have the correct size of conduit before you begin installation.

Additionally, you will want to consider adding some allowance for future expansion or installation of additional cables. This can minimize future project costs, avoiding the need for an entirely new installation.

Step 3: Measure Conduit Runs

Next, you will physically measure the distance of the run. Measure each run between access points, like pull boxes or terminal ends. Be as accurate as possible to avoid under-estimating (which can stall your project as you wait on new deliveries) or over-estimating (which unnecessarily increases project costs).

Be sure to take into account any bends, turns, or obstacles along the planned path. HDPE conduit can be bent to avoid some obstacles, but there are limits to how much you can bend your conduit.  You will need to stay within the manufacturer guidelines to avoid damaging cables and conduit. See our articles on Calculating Conduit & Pipe Bends for information about how to calculate bends and our article about How to Bend Conduit for information about completing the actual bends. Also, make note of any couplings or fittings that will be needed along the run.

Step 5: Calculate Total Conduit Length

Add up all the conduit lengths measured in step 3, and any allowance you have calculated for future expansion. This will be the minimum amount of conduit required for the installation.
Once you have the above total, you may want to add in a small allowance for waste/mistakes and unforeseen challenges in the run. That will help ensure your project doesn’t stall while you wait for additional conduit to arrive.

Step 6: Verify Compliance with Codes and Regulations

Before finalizing your estimate, make sure your design complies with all NEC and local electrical codes and regulations. Double-check conduit spacing, depth, and support requirements, making necessary adjustments.