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Conduit Fill Calculation

The below tool will assist to perform NEC conduit fill calculation.


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Conduit Area : sq in
Total Wire Area : sq in
Conduit Fill : %

How is conduit fill calculated ?

Conduit fill and sizing should be complied with Table 1 of NEC Chapter 9.

Total Cable Area / Total Conduit Area < Allowable Percent Fill


Total Cable Area:∑ (Cable Overall Diameter^2 / 4 * 3.14)
Total Conduit Area:As NEC 2017 Chapter 9 – Table 4
Allowable Percent Fill:– 53% for 1 no. of cable
– 31% for 2 nos. of cable
– 40% for over 2 nos. of cable

Conduit fill calculation result is based on normal conditions of good practice cable routing and alignment of conductors. For example, the total number of bends between 2 pull points can not exceed 360o or the maximum number of conductors in a connection box.

RMC conduit size, internal diameter and internal total area of is as below:

For other type of conduit (i.e. ENT or PVC-80), refer to chapter 9 – Table 4.