Scale simulation: cables (red) inside the recommended Techduto NBR conduit
Notice: approximate result per NBR 5410, based on the catalog dimensions of the Techduto NBR line (NBR 15.715). Does not replace an electrical project signed by a licensed professional (CREA/ART). Also check the specific requirements of your local utility company.
It’s not bureaucracy — the standard prevents two real physical problems: heat buildup and friction when pulling the cable.
A cable packed too tightly inside the conduit can’t exchange heat with the environment. Temperature rises and the insulation degrades faster than it should.
An overfilled conduit creates friction when pulling the cable through. On bends, cables can literally jam against the wall — what the industry calls jam ratio.
It sounds counterintuitive, but it’s geometry, not cable physics. 2 cables side by side inside a round conduit leave dead space and tend to twist during installation — a fill ratio of only 31%. With 3 or more cables, they settle into a more compact, stable arrangement — a 40% ratio.
Fill ratio is not the same as the grouping factor (Table 42 of NBR 5410) — fill ratio ensures the cables fit and can be pulled without damage; the grouping factor, calculated separately, ensures the wiring doesn’t overheat when several circuits share the same conduit. This calculator only handles the first one. And don’t confuse it with NR-10 (workplace safety in electrical installations) — they’re different things: NR-10 doesn’t size anything.
Internal testing: the cable-diameter-by-gauge table still uses market reference values, not yet confirmed against an approved manufacturer datasheet. The conduit dimensions (DN/Ø) already come from Techduto’s official technical catalog. Do not use this result in a real project until that table has been validated.
Our engineers can validate the calculations and specify the ideal solution.
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