Conduit Size

As part of the mandatory requirements of the National Electric Code (NEC) conduit sizing is calculated based on the conductor and conduit type. Since conduit and tubing from different manufacturers have different internal diameters for the same trade size, the calculation is based on actual area and fill percentages. This correlates to Table 9 and Informative Annex C of the NEC.

The 60% fill permits conduit or tubing nipples of 24 inches or less in length to have a conductor fill of up to 60%.

The 40% fill includes use of more than 2 wires.

The National Electric Code (NEC) specifies the minimum size for cable tray systems which includes ladder, ventilated trough, ventilated channel, solid bottom and other similar structures. It’s important to note that cable trays are mechanical support systems and not raceways. Raceways are included in another section of the code.

Proper cable tray sizing is complicated and often existing cable trays are overloaded per the code. If you have questions or would like some engineering assistance to properly size your cable tray installation please contact us.