NEC Fill Ratio
This calculator will help you determine the number of cables that can be installed according to the National Electric Code (NEC) guidelines for Fill Ratio. This is applicable to cables preinstalled in Conduit up to 3” by Dura-Line, or field installed.
Begin at Step 1 with the Inner Diameter 
of your Conduit.
Select Smoothwall or Exact ID
Select Smoothwall if you know your Product or Enter your Exact ID
Dura-Line’s cable fill calculator estimates the allowable cable fill by comparing the cross-sectional areas of both single or multiple cables to the proposed trade size conduit’s inside diameter’s cross-sectional area. The maximum allowable fill should not exceed the recommended percentages in accordance with article 347 of the NEC, National Electric Code for cables that are not lead covered. Calculations for determining maximum allowable cable fill per the NEC permits the following fill percentages; for one (1) cable is 53%, for 2 cables is 31%, for 3 or more cables is 40%. The permissible cable fill percentage is one variable, if cables are to be field installed other variables should be considered including but not limited to; cable weight, length of pull, changes in direction or elevation to name a few. Pre-installed cable assembly is an additional consideration for CIC. For example, plexed as opposed to parallel cable constructions may be further limiting factors in the number of size of cables that can be pre-installed.
This information should be confirmed prior to ordering and Dura-Line assumes no liability for damages resulting from the use of these calculations for conduit sizing. For more detailed analysis and support before, during, and after conduit selection to ensure you are choosing the optimal product for your needs, please contact a Dura-Line specialist.