Raceway Conduit Fill Calculator
Raceways must be sized so that conductors can be easily pulled and enough space is allotted between each conductor to prevent overheating. This program is in congruence with NEC Code and calculates the number of same size conductors that can be used in a single raceway. As per NEC, the tool limits the fill to 40% for over 2 conductors, 31% for only two conductors, and 53% for one conductor for standard raceway applications.
The exception to these percentages is when wire is used in seal-offs and nipples. For seal fittings, the fill may not exceed 25%. This is not specifically stated in the code, but is interpreted through the requirement that listed items be used in accordance with their listing. UL lists seal fittings for 25% fill. Nipples are defined as a conduit 2 feet or less in length and connects enclosures, boxes, gutters, wireways, etc., together. By applying the 60% rating, nipples do not have to be derated and more conductors can occupy the raceway.