Duct size relative to cable diameter: which description is correct?

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Multiple Choice

Duct size relative to cable diameter: which description is correct?

Ducts should provide a small but real clearance over the cable to ease installation and future pulling, without wasting space. The guideline used in practice is to select a duct inner diameter that is about 1.15 times the cable’s outer diameter, or, equivalently, about half a trade size larger than the cable’s trade size. This gives enough room for the jacket and lubricant, reduces friction when pulling, and still keeps duct fill reasonable for a single cable. Choosing a duct only the same size as the cable would have no clearance and could snag the cable or damage it. A duct much larger than the cable (like twice the diameter) is unnecessary and inefficient. Therefore the 1.15x or half-trade-size-bigger rule best balances ease of installation with cost and space.

Ducts should provide a small but real clearance over the cable to ease installation and future pulling, without wasting space. The guideline used in practice is to select a duct inner diameter that is about 1.15 times the cable’s outer diameter, or, equivalently, about half a trade size larger than the cable’s trade size. This gives enough room for the jacket and lubricant, reduces friction when pulling, and still keeps duct fill reasonable for a single cable.

Choosing a duct only the same size as the cable would have no clearance and could snag the cable or damage it. A duct much larger than the cable (like twice the diameter) is unnecessary and inefficient. Therefore the 1.15x or half-trade-size-bigger rule best balances ease of installation with cost and space.

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