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Conduit Fill
Conduit size for cable bundle at 40% fill.
ElectricalCore inputs only — quick sizing with engineering defaults.
Inputs (SI units)
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Engineering Formula
- A_cables = N × π × d² / 4
- A_conduit_min = A_cables / fill%
- d_conduit = √(4 × A_conduit / π)
NEC Chapter 9 caps fill at 53% for one cable, 31% for two, 40% for ≥3. IS 732 uses similar limits.
Step-by-step Calculation
- 1.Bundle area
N·πd²/4678.6 mm² - 2.Conduit area
A/fill1,696.5 mm² - 3.Diameter
√(4A/π)46.5 mm
Design Assumptions
- • Round cables of uniform OD.
- • No derating for ambient / grouping.
Engineering Tips
- ◆Reduce fill 10% for long pulls > 20 m.
- ◆Prefer HDPE conduit for outdoor solar runs.
Warnings
- ▲Overfill traps heat and fails IEC ampacity.
Standards & References
NEC Ch. 9 T1IEC 61386IS 732
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