Check conductor fill percentage against the allowable limit for a conduit.
Fill limits exist so conductors can be pulled without damage and so heat can escape. The limit tightens for two conductors because that arrangement leaves the least usable space. Overfilled conduit is a common inspection failure, and it also forces ampacity derating that can undo the point of the larger cable.
Conduit Fill
Fill = total conductor area ÷ conduit internal area; the limit is 40 per cent above two conductors
Fill = total conductor area ÷ conduit internal area; the limit is 40 per cent above two conductors Fill limits exist so conductors can be pulled without damage and so heat can escape. The limit tightens for two conductors because that arrangement leaves the least usable space.
Overfilled conduit is a common inspection failure, and it also forces ampacity derating that can undo the point of the larger cable.
This calculator takes 3 inputs: Conduit internal diameter, Number of conductors, Conductor outer diameter. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.